Potential Possibilities of Using Peat, Humic Substances, and Sulfurous Waters in Cosmetology

Abstract

Balneology is one of the oldest fields of medicine related to the use of natural raw materials (medicinal waters, medicinal gases, peloids, climatic values) in the treatment, prevention, and rehabilitation of many diseases but also increasingly in cosmetology. Currently, balneotherapy (spa therapy) combines tradition and modernity. The interest in spa treatments, the popularity of a healthy lifestyle, as well as the constant search for active substances of a natural origin for cosmetics make peloids, medicinal, and mineral waters very popular in the cosmetics industry. The main aim of this review was to present current, scientifically proven knowledge about the potential use of peat, huic substances, and sulfurous water in cosmetology. The work describes the potential possibilities of using medicinal waters, especially sulfurous waters, as well as peats and humic compounds, which are the source of active substances with biological activity e.g., antibacterial, anti-inflammatory, and antioxidant, and possess a positive effect on psoriasis, atopic dermatitis, or acne. The therapeutic effects of these substances have been well documented in the literature; however, the validity of their use in cosmetology requires further confirmation.

1. Introduction

Balneology (from Latin balneum—bath; from Greek lógos—word, science) is the scientific field of spa medicine that studies the use of natural healing resources, mainly mineral waters (hydrotherapy), therapeutic gases (gasotherapy), and peloids (peloidotherapy) for prophylactic, curative, and rehabilitative purposes (Figure 1) [1,2,3].

The tradition of using hydrotherapy and peloidotherapy dates back to ancient times and Greek, Roman, and Egyptian civilizations [2,6,7]. Hydrotherapy (also known as water cure) is a stimulus treatment using the external therapeutic effects of water in the form of baths, showers, pours, and other treatments.

Hydrotherapy uses the thermal, mechanical, and chemical effects of water to increase the general resistance of the body, reduce stress, or treat a number of conditions (e.g., the musculoskeletal system, circulatory system, heart system diseases, injuries, etc.). Hydrotherapy procedures are mainly used in spas and physiotherapy facilities. Local and general water treatments are also an excellent preparation for massage and other cosmetological procedures [6,8].

Peloid (from Greek pelos—mud) is defined as “a mature mud or mud suspension or dispersion with curative or cosmetic properties, consisting of a complex mixture of fine grained materials of geological and/or biological origin, mineral or sea water, and organic compounds commonly arising from some biological metabolic activity” [9,10]. In Poland, peat, called “black gold”, is very popular as a balneological raw material due to the large resources of the raw material and the long tradition of use in spa treatment. In 1968, the International Peatland Society (IPS) was founded in Quebec (Canada). IPS is an organization of individual, corporate, and institutional members dedicated to the responsible management and wise use of peatlands and peat. It is currently based in Finland and brings together individual, corporate, student, institutional, and NGO members from 38 countries. The main goal of this association is to promote peatlands and peat, collecting, exchanging, and transmitting knowledge and experiences through events and projects addressing key issues, including climate change, biodiversity, the need for responsible use, and restoration. The IPS regularly organizes conferences, symposia, and workshops and publishes the results of scientific and industrial research [9].

Another element of balneotherapy involves the use of natural gases, ranging from usual gases (oxygen and carbon dioxide, to gases like nitric oxide, carbon monoxide, and hydrogen sulfide. CO₂ balneotherapy is a non-invasive, highly effective, and inexpensive treatment whose effects are related to its effect on the release of free radicals and the reduction in oxidative stress. Hydrogen sulfide (H₂S) is both an exogenous therapeutic gas, found in sulfurous waters, with well-known and appraised medicinal properties in balneotherapy, and also an endogenous gaseous signal molecule in organisms (following nitric oxide (NO) and carbon monoxide (CO), which plays a vital role in various systems and diseases) [4].

Natural substances have been used in cosmetology for a long time. Women made special recipes from products that were available in everyday life. They were used in the form of liquids, powders, mixtures, abrasives, and cosmetics for facial, body, and hair care. Typically, naturally available products were used, such as extracts, infusions of various plant species, mineral substances (clays), or natural abrasives made from coffee and fruit seeds. In ancient Egypt, women bathed in sour milk. Currently, natural ingredients are very popular in cosmetics. Increasingly, producers are releasing special cosmetic lines based only on natural substances [5]. The main aim of this review was to present current, scientifically proven knowledge about the potential use of peat, humic substances, and sulfurous water in cosmetology. The present review focused on the possible applications of natural products from various biological sources in skin care cosmetics, concentrating on work that appeared in the literature up to June 2024.

The topic of the use of balneological methods for prevention, treatment, and rehabilitation is very broad, so this review focused on peats and humic compounds, as well as the sulfurous waters, in the context of their cosmetic use in particular.

2. Materials and Methods

This study was a narrative review summarizing scientific reports on the possible applications of peat, humic substances, and sulfurous water in cosmetology. The aim of this work was to revise the latest investigations that can shed light on this matter. PubMed and Scopus databases were reviewed up to June 2024. Search terms included “balneotherapy”, “spa therapy”, “peat”, “peat therapy”, “peat cosmetology”, “humic acids”, “humic and fulvic substances in cosmetology”, “mineral water”, “sulfurous water”, “sulphurous water cosmetic”, and “sulfurous water cosmetology” in the abstract, title, and key words. The obtained articles were evaluated for scientific evidence related to peat and sulfurous water in use in cosmetology. Duplicate articles, those with no full text available, letters to the editor, and case reports were excluded.

3. Peat

3.1. General Characteristics

Peat is one of the most important natural raw materials in Poland. This peloid is formed as a result of the incomplete decomposition and humification of plant remains in high-humidity conditions under the influence of humifying, anaerobic bacteria but also fungi, algae, or microscopic water creatures [10,11]. Peat is also named as turf (in Polish, “borowina”) and the areas where peat occurs are called peatlands, bogs, mires, moors, or muskegs [12].

Due to the lack of consistent terminology allowing for a clear definition of peatlands, it is difficult to determine their exact global area. The international terminology of wetlands and peat bogs may be unclear because different languages have common names with different meanings and there are different criteria for distinguishing peat from other types of biogenic sediments [13].

The physical and chemical effects of peat in cosmetics depend on the content of active substances in this peloid [14]. Humic compounds (humic acids, fulvic acids, and humins) show high biological activity and are the basic group of active substances that are credited with the action of peat, attracting the greatest attention of researchers around the world.

The potential use of peat in cosmetology is primarily related to the action of humic acids, including antimicrobial [15,16,17,18,19], anti-inflammatory [20,21,22,23,24], and antioxidant [25,26,27,28], which has been demonstrated in the context of the treatment of various diseases. Modern knowledge regarding the health-promoting and cosmetic uses of peat is based mainly on the action of humic compounds, which constitute the main group of active substances. Unlike raw peat, the composition of which is variable and dependent on many factors, humic compounds can be precisely tested quantitatively and qualitatively [29].

Comprehensiveness and combining several treatment methods are very important in balneological treatment. This allows for an enhanced improvement effect, thanks to the mutual interaction and complementation of various stimuli. Therefore, spa treatments often use a combination of peloids and medicinal waters [9].

3.2. Formation and Division of Peats

A peat bog is a type of wetlands that is poorly oxygenated with hardly permeable soil, specific vegetation (swamp and swamp–meadow plants’ habitats), and organic sediment accumulation processes. It may be formed by the landfilling of aquatic environments (terrestrialization) or marshy terrestrial environments (paludification) [30,31]. Most habitats where peat is formed consist of two layers, the upper (acrotelm), oxygenated layer, in which intensive decomposition of organic matter occurs during periods of lower groundwater levels. In deeper, less oxygenated layers (catotelm), the decomposition of organic matter is slow. The boundary between these layers is determined by the level of the minimum water table in summer and is approximately 10–50 cm. According to some criteria, the minimum thickness of peat should be 20–70 cm so that a given habitat can be called a peat bog [9].

Peatlands cover approximately 4 million km², of which 3.460 million km² (around 80%) are peat bogs in the boreal and subarctic zones, and they store one-third of global soil carbon [15,16]. Almost one-third of European peat deposits are found in Finland, one-fourth are found in Sweden, and the remaining amount is found in Poland, Great Britain, Norway, Germany, Ireland, Estonia, the Netherlands, France, and Latvia [30,31].

Currently, there is no uniform peat classification system and there are different divisions depending on the scientific discipline or country. The division of peat is based on differences in topography, geomorphology, type of vegetation, and physical and chemical features [32]. The basic differences are presented in

Table 1. The most important features of low and high peat bogs [32].

Features of the Peat Bog	Subtype of Peat Bogs
	Low-Moor Sphagnum Peat	High-Moor Sphagnum Peat
Water supply	groundwater, lake water	rainwater only
Nutrients	high content	low content
Water capacity	moderate	very large
Plant species’ composition	rich	poor
Dominant ingredient	vascular plants	sphagnum mosses
pH	neutral to acidic	strongly acidic
Content of organic parts in dry matter	95%	75%
Area of occurrence in Poland	6.5%	89%
Other	high water absorption and sedimentation volume, high sorption properties, low thermal conductivity

.

Depending on the usage purposes, peat can be also characterized in numerous ways. The most important chemical and physical properties important for the environment, as well as for many areas of the economy and industry, are presented in

Table 2. The most important physical and chemical properties of peat [34].

Chemical Properties	Physical Properties
Composition (organic and mineral compounds) Nitrogen Phosphorus Sulfur CaCO3-free lime Trace elements	Water management Water retention Available water content Hydraulic conductivity Sater holding capacity
pH	Bulk-density
Organic carbon	Porosity
Cation exchange capacity	Irreversible drying
	Swelling and shrinking

. Water retention is a very important parameter assessing the suitability of peat and depends mainly on the content of humic acids. This parameter increases with the increase in the concentration of humic acids (in high-moor sphagnum, peat is higher) and with an increasing degree of decomposition (usually higher in low-moor sphagnum peat due to the higher content of aerobic and anaerobic bacteria and fungi) [33]. To determine the degree of decomposition (the ratio of cellulose and hemicellulose to the concentration of humic acids), a 10-point von Post scale is used, marked with symbols from H1 to H10. The higher the degree of decomposition is, the higher the value is on the scale and, thus, the better the healing properties are of the peloid. In Poland, peat with a degree of decomposition from H6 to H10 is used in medicine. This method was developed for homogeneous peats, in their natural state, fully hydrated, and originating from raised bogs. It is not used in the case of low peat, which is often silty, due to low accuracy [33,34].

3.3. Peat Composition

In terms of chemical composition, peat is a mixture of organic compounds, mineral substances, and water. There are two processes that influence the composition and properties of peat. The first is humification, in which decomposition occurs and the formation of the humic compounds’ characteristic of peat deposits occurs. The second is during mineralization, which involves the decomposition of organic substances to produce mineral compounds (carbon dioxide, ammonia, phosphate, or sulfate ions) [32].

The carbon content in various types of peat is 50–60% dry matter and is increasing with the degree of its decomposition. The oxygen content in peat is 33–40% dry weight (DW) and is higher for low-moor sphagnum peat. Knowledge about the oxygen and carbon contents allows us to determine the degree of mud decomposition and its age. The hydrogen content in peat is approximately 6% of DW. It is found in peats approx. 0.5–4.0% of DW nitrogen, which occurs mainly in an organic form, and 0.1–1% of DW sulfur [34].

Table 3. Chemical composition of peat [10,34].

Organic compounds	Humic compounds:	humic acids fulvic acids humins
	Bitumens:	resins waxes steroids
	Others:	monosaccharides and their derivatives (amino sugars, uronic acids, aldonic acids) oligosaccharides (sucrose, lactose) polysaccharides (cellulose, hemicellulose, starch) proteins pectins lignin lipids hemicellulose cellulose polyphenols
	Small amounts:	nucleic acids, pigments, alkaloids, vitamins (mainly of the B group)
	Microflora:	aerobic and anaerobic bacteria fungi
Inorganic compounds	Chlorides Sulfates Bicarbonates Calcium Magnesium Sodium Potassium Aluminum	Iron Manganese Copper Cobalt Zinc Iodine Fluorine Bromine

shows the chemical composition of the peat [10].

Humic compounds (mainly humic acids, fulvic acids, and humins) are the most important organic compounds found in peat as a source of energy, carbon, and nitrogen for soil microorganisms and plants. They are polymers with high molecular weight and diverse structures. They are rare in unbound soil and are usually bound to minerals to form salts of humic compounds (fulvine acids, humates), humic complexes and intra-complex compounds (chelates), and combinations of humic compounds with clay minerals [10]. A high content of humic compounds occurs primarily in humus soil, peat, and sapropel [35]. Their chemical form is influenced by, among others, conditions in which the process of peating (humification) of plants takes place and their type, duration of humification, and hydration of the local environment [36]

Humic acids (10–43%) are considered the most important biologically active constituents of peat. Because of the diversity and variability of humic acids, it is not possible to establish a clear structure. These are high-molecular-weight compounds consisting of an aromatic core connected by bonds with amino acids, sugars, peptides, aliphatic acids, and other ingredients with an aliphatic structure. The core consists of aromatic rings of the phenol type or containing cyclic compounds’ nitrogen. Reactive groups are an important element of the structure of molecules, such as the carboxyl (–COOH), methoxy (–OCH₃), carbonyl (O=C<), hydroxyl (–OH), and quinone groups [37].

Peats also contain yellow-brown fulvic acids (5.5–25%), soluble in water over the entire pH range. They are compounds with a lower molecular weight and a larger number of aliphatic groups compared to humic acids. Obtained from low-moor sphagnum peat, they are characterized by a lower carbon content, the number of carboxyl and phenolic groups, and more hydrogen, nitrogen, oxygen, and methoxy groups than fulvic acids from high-moor sphagnum peat. Their content decreases with an increasing peat depth

Peat is also a source of slightly soluble bitumens (7–22%), which do not improve the soil structure but give it a more hydrophobic character. This group of compounds includes waxes and tars. Bitumen content in peat increases with age, depth of the deposit, and the degree of humification. The least researched humic substances, non-participating in soil transformation processes, include humins characterized by a black color and insolubility over the entire pH range [38].

3.4. Pharmacological and Biological Activity of Peat and Humic Substances

Medical and hygienic uses of peat date back to the 18th century. Peat has long been used in many fields of medicine, such as rheumatology, physiotherapy, and sports medicine, and increasingly in dermatology and cosmetology [24]. In traditional folk medicine, peat was used to treat skin diseases, cold stress, rheumatic pain, diabetes, kidney stones, heart ailments, leprosy, and immune system diseases [22,39]. Examples of historical and contemporary uses of peat for internal use in the treatment of various ailments include radioprotective [40], hepatoprotective [41], neuroprotective [42], and antihypoxic [43,44] uses as well as renal ischemia [45] and cardiovascular diseases [46].

In Poland, peloids are the second most frequently used natural resource after medicinal waters [47]. The peat preparation patented in 1991 by Professor Tołpa enjoyed great fame [48]. It has been attributed to many medical uses, including anti-cancer properties, but no medical (internal) benefits have ever been confirmed by reliable scientific research. In the 1900s, Polish scientists conducted intensive research on the Tołpa peat preparation, aimed at confirming its effectiveness, including antioxidant, anti-cancer, and hepatoprotective properties; uses against gastric and duodenal ulcers, against respiratory tract infections, and on sinusitis and cervicitis; as well as in immunology, allergology, hematology, and angiology [49,50,51].

The immunomodulatory effect of peat has been demonstrated by influencing the activation of neutrophils and macrophages, inducing the production of interferon and tumor necrosis factor in human peripheral blood leukocytes, as well as NK cells [52,53]. In the study by Çalışır et al. [54], they demonstrated a beneficial effect of humic acids administered systemically on the condition of periodontal tissues in rats with induced periodontitis. The influence of these compounds on the level of interleukin (IL)-1β and IL-10 in serum and gingival homogenates, the number of osteoclasts, and osteoblastic activity were observed. Additionally, the influence of humic acids on the healing of aphthous ulcers in the oral cavity has also been demonstrated. The influence of fulvic acids on the pathogenesis of atopic dermatitis has also been demonstrated. The local action of these compounds involves the downregulation of CCL17 and CCL22, inhibition of P38 MAPK, and JNK phosphorylation [55]. In the study by Verillo et al. [56], the anti-inflammatory activity of humic acids was evaluated on HaCaT cells. A decrease in the gene expression of the cytokines IL-6 and IL-1β was observed.

The anti-inflammatory and immunomodulatory effects of peat are primarily related to its antioxidant and anti-free radical properties [24,25,26,27,57]. The anti-free radical effect of humic substances results from the presence of phenolic groups and non-phenolic groups in their structure, including carbohydrate fragments [58]. Tarnawski et al. [59] demonstrated also the presence of phenolic acids in peat extracts and confirmed their antioxidant effect. Phenolic acids may originate directly from biomass or from the breakdown of humic substances or are a product of the Maillard reaction. Humic acids also have the ability to chelate heavy metals, e.g., cadmium, from the body. The potential impact of radioisotopes as active substances responsible for the effects of peat was also examined [60].

Both peat extracts and humic and fulvic acids isolated from them exert antimicrobial activity in vitro. Antibacterial activities have been shown against many bacteria including Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae as well as against Candida albicans [13,16]. Humic acids and poly(OH)carboxylates isolated from peat are also selective inhibitors of the replication of the Herpes simplex virus and Cytomegalovirus [17,61].

Schneider et al. [18] showed that the synthetic humic acid analogue inhibits the infectivity of HIV particles by interference with a V3 loop-mediated step of viral entry. Similar properties have been proven for oxihumate, which inhibits the HIV-1 infection of MT-2 cells and increases the proliferative response of human lymphocytes [62].

3.5. Potential Uses of Peat and Humic Compounds

3.5.1. Types of Peat Preparations

Oral administration of a preparation containing humic acids influenced fermentation in the colon and positively modified the intestinal microbiota. This phenomenon can be used in the production of preparations used to rebuild the intestinal microflora, e.g., after antibiotic therapy, inflammation of the digestive tract, or metabolic diseases [63,64]. Peat preparations are, however, mainly used as products for external use in cases of hematoma, phlebitis, dehiscence, myogelosis, arthrosis, polyarthritis, osteochondrosis, and osteoarthritis, among others [24,39]. In addition to unprocessed peat (peat pulp), the following are used for therapeutic purposes: peat patches, ointments, hydrogels, and gynecological tampons [61]. An interesting example of the use of humic acids is the production of active polymeric transdermal hydrogel materials. It was shown that the addition of up to 5% humic acids increased the strength and improved the structure of the polymer, which can be used in the production of transdermal systems [65]. Peat is also used in cosmetic products and is particularly popular in dermocosmetics and natural cosmetics [61].

• Peat in Cosmetics

The popularity of treatments using peat has remained high in Poland but also in other regions of Europe for many years. Currently in Poland, also cosmetics containing peat are very popular. These include preparations such as gels, ointments, pastes for compresses, toothpastes, creams, dental gels, bath emulsions, shampoos, and peat briquettes [47]. Although drugs containing Tołpa peat have been withdrawn from the pharmaceutical market, the Tołpa company has remained one of the leading producers of cosmetics in Poland for the face, body, and hair and oral hygiene since 1989 [66]. Concentrated peat extract has been produced by Torf Corporation on the basis of a patented technology developed by Prof. Stanislaw Tolpa and his co-workers. The production technology involves the alkaline extraction of peat, acidification to remove a humic acid fraction, and concentration connected with thermal processing [59]. These are “dermocosmetics” and “ecocosmetics” available for individual customers but also specialist cosmetics intended for professional treatments in spa and wellness centers and health resorts. Peat and humic acids as a cosmetic raw material also appear in the recipes of cosmetics produced in other countries, as shown in

Table 4. Examples of cosmetic products containing peat/mud water.

Producer	Country of Origin	Trade Name	Cosmetic Form	Type of Mud in the Cosmetic Composition (INCI)	Properties of the Cosmetic According to the Producer	Ref.
NeoGenesis	United States	Fresh Face	Mask	Peat	Rejuvenation Gentle exfoliation No irritation	[67]
Lumene	Finland	Nutri-Recharging	Cleanser in Foam	Peat	Purification	[68]
Dr Duda	Poland	Mud shower gel	Shower Gel	Peat	Purification Strengthening the skin Skin nourishment	[69]
Body blitz	Canada	Eucalyptus Mineral Scrub	Scrub	Peat	Circulation stimulation Exfoliation Improved appearance	[70]
Misoli	Korea	Shining Care Black Pearl	Eye Patch	Peat Water	Reduction in dark circles under the eyes Reduction in swelling Smoothing wrinkles	[71]
Epielle K-Beauty	Korea	Deep Pore Charcoal	Cleanser	Peat Water	Deep cleansing Detoxification Energizing the skin	[72]
Dr Hauschka	Germany	Moor Lavender Calming Bath Essence	Bath Essence	Peat Moss Extract	Relaxation Body strengthening Warming up	[73]
La Le	Poland	Mud hydrolate with linden	Hydrolate	Peat Moss Extract	Purification Toning Regulation of sebum secretion	[74]
Tołpa	Poland	Max Effect Anti-fatigue	Cream	Peat Extract	Soothes irritations Redness reduction Improved flexibility	[66]
Sabbatical Beauty	United States	Piper’s Peat Serum	Serum	Peat Extract	Reducing the visibility of pores Purification Anti-aging Anti-inflammatory Soothing irritations	[75]
Bingospa	Poland	Peat Shampoo	Shampoo	Peat Extract	Improved circulation Anti-inflammatory Soothing irritations	[76]
Sulphur	Poland	Buskodent	Gel for Gums	Peat Extract	Preventing loosening and falling out of teeth Reducing bleeding gums Strengthening the periodontium Breath freshening	[77]
Gorvita	Poland	Mud Ointment	Ointment	Peat Extract	Anti-inflammatory Soothing irritations An alternative to mud compresses	[78]
CD Formulation	United States	Raw Material	-	Humic Acids	Chelating agent	[79]
Osmosis	United States	Nutrient Activating Mist	Mist	Humic Acids	Skin conditioning, chelating agent, skin-conditioning agent	[80]
Spoiled Child	United States	Spoiled Child A22 Biotin Boost Hair + Scalp Serum	Hair and Scalp Serum	Humic Acids	Skin conditioning, chelating agent, skin-conditioning agent	[81]

.

• Humic Compounds in Cosmetics

Humic acids are used in clinical practice, dermatology, but also increasingly in cosmetology [61]. It has been shown that substances with low molecular weight (<1000 Da), mainly humic acids, are responsible for the stimulating effect of peat on the skin [82].

The basic parameter influencing the effectiveness of peat in cosmetics and treatments is the processing of the raw material, for example, the method of extraction of humic compounds. A great difficulty and challenge for scientists is the extraction process of these compounds, which is time consuming, expensive, and difficult to reproduce [14]. While in the case of a treatment such as a bath or compress, the type of peat (its chemical composition), the treatment time, and the temperature of the raw material are the most important, in the case of using the peat in a cosmetic preparation, the most important thing is the processing, which allows for the isolation of active substances, mainly humic compounds [39,82,83].

Humic substances have astringent and anti-inflammatory properties; therefore, they have the potential to be used in skin diseases such as atopic dermatitis, cheiropodopompholyx, psoriasis, and mild focal hyperhidrosis [61]. They may also be used in rosacea due to their ability to reduce redness and inflammation [84,85]. The photoprotective properties of humic acids have also been demonstrated. The behavior of Escherichia coli immersed in water systems enriched with humic acids was studied under the conditions of PAR, UV-A, UV-B, and simulated solar radiation. The protection provided by humic acids against light radiation is probably due to their ability to absorb this radiation and thus reduce the amount of energy reaching cells. This phenomenon can be used in the production of photoprotective cosmetics [86].

The Klavins and Purmalis study [87] demonstrated the ability of humic substances of a natural origin to reduce surface tension, while industrially produced humic materials had no or only a very slight effect on surface tension. This phenomenon can be used in various industries, including cosmetology, especially in the production of cleansing cosmetics.

Silamikele et al. [88] patented in 2015 a complex combining ethanolic peat extract with isolated humic acids. The obtained complex exhibited antioxidant activity and the ability to promote skin cell proliferation, which makes it a potential ingredient of anti-aging cosmetics. Also, the content of antioxidant substances (such as phenolic acids and flavonoids) and, therefore, the anti-free radical effect depends on the peat extraction method [59].

The invention of Kallio et al. [89] relates to a method of extract composition control in peat extraction by carbon dioxide, in which method the extraction temperature is 5–120 °C, pressure is 70–1000 bar, and the extraction is conducted in the presence of a modifier. The invention also relates to a peat extract comprising sterols and use of it in skin care or keratin fiber care products, general hygiene products and/or cosmetic products.

3.5.2. Types of Peat Treatments

Traditional treatments using mud in health resorts and spa and wellness centers are baths (total or partial), wraps (total or partial), compresses, iontophoresis, and phonophoresis [90].

In dermatological diseases, the temperature of the peat should not exceed 37 °C; in musculoskeletal and rheumatic diseases, applications up to 45 °C are recommended. The thermal effect of peat is to dilate blood vessels, increase blood and lymph flow, and reduce muscle tension. In the case of diseases of the musculoskeletal system, this results in increased joint mobility and an analgesic effect [91,92]. In cosmetology, peat is used as a raw material in both body and facial treatments. In facial treatments, peat is applied in the form of creams, masks, and patches or by performing iontophoresis for oily and combination but also for aging skin and skin prone to allergies. For body treatments, mud is used in the form of masks, compresses, poultices, or baths, especially in the prevention of cellulite and stretch marks and for a slimming effect [93].

The physiological effect of the treatments is a complex action, based on the action of thermal, mechanical, and chemical factors, among other [91,93]. The effects of therapy may therefore vary depending on variables such as the presence of a thermal stimulus, the composition and concentration of active substances and salts, osmotic pressure, electrical conductivity and occlusion, or skin condition. The thermotherapy and occlusion techniques used in the treatments enhance transdermal transport, which allows for the delivery of the necessary active substances and elements to the skin, stimulation of cellular metabolism, and tissue detoxification [90,94,95]. Mechanical action consists in the peat mass of pressing the treated area, which stimulates the flow of blood and lymph [93]. The effectiveness of the treatment using mud depends also on the type of raw material and the treatment procedure (Figure 2).

Peat baths are the most popular form of peloidotherapy using this peloid for medical purposes The so-called peat pulp is used for bathing, heated to the appropriate temperature, usually 39–40 °C. There are two treatment procedures for bathing. For the first (total or half baths), special bathtubs are used and the peat is heated to 39 °C. In this case, it is required to immerse the entire body up to the neck for 10–20 min. Due to the cost of the treatment, total baths are replaced with suspension baths, in which a large dilution of peat is used. The second one (partial baths) includes the immersion of selected body parts, mainly limbs. The poor thermal conductivity of peat and high heat capacity ensure the deep and long-lasting heating of the body during the treatment. Baths cause the skin’s blood vessels to dilate and enlarged pores to narrow and they increase sweating, which leads to the detoxification process. The oxygenation and nourishment of the skin improves [3,96,97].

Peat pulp or peat patches are also used for peat compresses and wrapping. After applying a thick layer of peat to the treatment area, it should be tightly wrapped in foil. The duration of the treatment is about 20–30 min. Matuszewska et al. [93] described the effect of using peat compresses on the reduction in cellulite. A series of 10 treatments were performed on the skin of the thighs in 49 women with grade III cellulite (Nürnberger–Müller scale). To perform a series of treatments, peat from Połczyn (Poland) heated to a temperature of 40 °C was used. Beneficial effects in the form of increased hydration of the treatment area were observed already after the first treatment, while after five procedures, the firmness and tension of the skin improved. The result of the entire series of 10 treatments was the reduction in cellulite from grade III to II.

4. Medicinal Waters

4.1. General Characteristics

The therapeutic use of naturally occurring medicinal waters has been a cultural and medical tradition, especially in European countries [98].

Mineral baths have been used as therapeutic treatments since Roman times. Mainly, bubbling mineral waters containing sulfide salts were used, which were supposed to have a beneficial effect on the skin. Currently, medicinal waters are not only part of traditional medicine but also part of the public health systems of many countries, such as France, Italy, Spain, Poland, Israel, and Japan. The occurrence of sulfurous waters is associated with volcanic activity (Iceland, New Zealand, Indonesia). They are also located in areas where sulfur minerals such as gypsum or anhydrite occur (Poland, Russia, Slovenia, Germany, USA) [99].

The classification of thermal waters was given in 1933 by Marotta and Sica. It includes three parameters: temperature, fixed residue, and chemical composition [100].

Depending on the temperature, the following water types are distinguished: cold (temperature below 20 °C), hypothermal (between 20 and 30 °C), homeothermal (between 30 and 40 °C), and hyperthermal (between 40 and 50 °C) [101].

Medicinal waters are traditionally classified as simple thermal waters, simple acidic (carbonized) waters, alkaline (Na-K-biocarbonated waters), Ca-Mg-biocarbonated waters, chloridated (saline) waters, ironic (ferrous) waters, sulfurous waters, sulphated waters, iodated-bromidated waters, and radioactive waters [98]. The classification criteria are shown in Figure 3.

Natural mineral waters are subject to an authorization procedure carried out by the competent authorities of the European Union (EU) countries or by European Economic Area (EEA) countries. The lists of natural mineral waters officially recognized by the EU countries of the EU and of the EEA (Iceland and Norway) are published by the European Commission in the Official Journal of the European Union. These lists are regularly updated. Natural sources classified by the EU according to the list of 19 July 2024 are located in Belgium, Bulgaria, the Czech Republic, Denmark, Germany, Estonia, Ireland, Greece, Spain, France, Croatia, Italy, Cyprus, Latvia, Lithuania, Luxembourg, Hungary, the Netherlands, Austria, Poland, Portugal, Romania, Slovenia, Slovakia, Finland, Sweden, the United Kingdom (Northern Ireland), Norway, and Iceland [102].

In this work, we focused on the mechanism and biological activity of sulfurous water applied externally to the skin. Sulfurous water contains not less than 1 mg/L of total iodometric sulfur. The main components of this water include hydrogen sulfide, as well as hydrosulfides of alkali metals and other inorganic and organic sulfide-containing salts [31].

4.2. Sulphurous Water—Mechanism of Action on the Skin

Sulfurous medicinal waters are widely used in balneology. The therapeutic properties of these waters depend on the presence of divalent sulfur, mainly, H₂S (hydrogen sulfide), HS⁻ (bisulphides), S²⁻ (sulfides), Sn²⁻ (polysulphides) as well as other sulfur species [103]. Carbajo and Maraver [104] showed that the biological activity of divalent sulfur in sulfurous waters depends on many environmental factors such as pH, temperature, and redox potential. In natural waters, the oxidation processes take place, leading to the formation of polysulfides and thiosulfates.

The main active molecule in sulfurous water is hydrogen sulfide (H₂S). H₂S is a colorless gas with weak gas properties and is highly soluble in water. It has a characteristic smell of rotten eggs. H₂S is heavier than air, flammable, and corrosive. The concentration hazardous to health is considered to be 6 mg/m³. At a concentration of 300 mg/m³ it becomes undetectable due to the immediate paralysis of the olfactory nerve. H₂S burns in air to form sulfur dioxide (SO₂) or free sulfur (at low temperature and insufficient oxygen supply). Its stability depends on pH, temperature, and oxygen concentration in the environment. Sulfur species change at two critical pH values, pKa = 7.04 and pKa = 11.96. At physiological pH, the ratio of hydrogen sulfide to bisulphide (HS-) is 1:3. Identical H₂S solutions occurring at different ambient temperatures and in an oxygen environment show differences in concentration, and oxygen promotes the reduction in H₂S to hydrogen sulfate. At acidic pH, H₂S is the only form of sulfur [104].

The synthesis of H₂S in the body is based on the transformation of L-cysteine with the participation of the two most important enzymes: cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE). CBS converts L-cysteine and homocysteine to H₂S, and CSE catalyzes cystathionine cleavage [105]. Both mRNA and protein expressions of the enzymes CSE and CBS were observed in normal human keratinocytes. CSE and CBS also promote the resolution of inflammation in skin exposed to subcytotoxic concentrations of formaldehyde. The increase in the activity of both enzymes causes an increase in the concentration of H₂S, which may in turn inhibit the upregulation of pro-inflammatory activity mediators (such as MMP-1, PGE2, and IL-8) [106].

Endogenous H₂S regulates many important processes in the skin, such as inflammation [106], cell proliferation [107], apoptosis [108], and vasodilation [109]. The effect of H₂S on keratinocytes depends on the concentration of this compound. At low concentrations, it stimulates the proliferation of keratinocytes, while at high concentrations, it intensifies the apoptosis process. NO has a similar effect, which allows us to assume that the effects of H₂S in the skin (e.g., vasodilator) may be similar [108].

Studies have shown that hydrogen sulfide (H₂S) can contribute to the stimulation of angiogenesis and thus contribute to the activation of the wound-healing processes [110]. It was proven that, in mice with type 2 diabetes, the administration of sodium hydrosulfide (NaHS) for 18 days resulted in the activation of Ang-1 (angiopoietin-1) and restoring of EPC (endothelial progenitor cell), which has a pro-angiogenic effect [111]. H₂S possesses also the ability to quickly move through cell membranes without the help of transmitters, which cause a variety of biological reactions [110].

The skin is a tissue that stores sulfur. It is estimated that it accumulates approximately 60 mg per 100 g of tissue. A part of sulfur penetrates the human body and forms chondroitin-sulfuric acid as a result of combining with hydrocarbons, which is a component of cartilage and synovial fluid. Moreover, as a result of these combinations, mucoitin-sulfuric acid is formed—a component of mucus. The following concentrations occur in sulfide water used in balneotherapy: high, >100 mg H₂S/L; medium, 50–100 mg H₂S/L; and weak, <50 mg H₂S/L. H₂S is absorbed through the skin and forms polysulfurides, which are easily soluble in fats and next penetrate the tissue capillaries and reach the general circulation. In order to investigate the migration of sulfur through the skin, research was carried out using radioisotopes of this element. These studies showed that sulfur absorbed through the skin from water is incorporated into protein molecules. In addition, it was shown that H₂S absorbed through the skin can increase the level of glutathione in the blood and antioxidant capacity, stimulates neuroreceptors in the skin, improves metabolic processes in the skin, and also reduces itching and has a soothing effect [99].

High concentrations of sulfide water have a keratolytic effect, softening and exfoliating the epidermis. This is the result of sulfur compounds binding to sweat and forming ammonium sulfide. Moreover, it has antibacterial and antiparasitic properties [106]. Exfoliation of the epidermis occurs as a result of various chemical reactions. Sulfur eliminates the disulfide bonds in cystine, resulting in the formation of two cysteine molecules that promote the exfoliation process [104].

4.3. Biological Activity of Sulphurous Water

Sulfide waters are used in balneotherapy mainly in the form of baths for diseases of the musculoskeletal system (rheumatic diseases, osteoarthritis, or arteriosclerosis) [99,112,113,114], peripheral nervous system [115,116], dermatoses [117,118,119,120], circulatory system [121,122], and respiratory system [123,124,125] as well as in many other diseases. The therapeutic effect of sulfurous waters is related to their anti-inflammatory, antioxidant, and antimicrobial activity, among others (

Table 5. Directions and general mechanisms of biological activity of sulfurous water used in the form of baths or inhalation.

Activity	Mechanism of Action	Ref.
Effects on the skeletal system	-induction of osteogenic differentiation of hMSCs	[112]
	-decreases in the activity of alkaline phosphatase -increases in the concentration of osteocalcin and phosphorus in the serum	[113]
	-improvement in quality of life of patients -reduction in the consumption of symptomatic drugs	[114]
Anti-inflammatory effect	-decreases the expression of IL-1α -downregulation of the expression of TNFα	[126]
	-increases in level of IL-10	[127]
Effect on the respiratory system	-increases in citrulline levels -decrease in ornithine levels	[123]
	-increases in the impedance curves that correspond to the normal ventilation of the tympanic box -decreases in pathological impedance curves	[123]
	-decreases in IgE concentration -increases in IgA concentration	[124]
Effect on the muscular system	-improves Visual Analogue Scale (VAS) score, -alleviates muscle spasms, -alleviates local tenderness, -enhances flexion–extension and rotation of the spine -improves the Schober’s index	[114]
Antioxidant activity	-decreases in values of total oxidative stress (TOS) and oxidative stress index (OSI) -increases in total antioxidant capacity (TAC) and total nitric oxide (NOX) levels	[128]
	-reduction in peroxide concentrations and SOD activities	[129]
	-inhibition of DNA damage	[130]
Antimicrobial activity	-reduction in growth of E. coli, E. faecalis, and S. aureus	[131]

).

4.3.1. Anti-Inflammatory Activity

The influence of various thermal mineral waters from two traditional and historical thermal resorts of Turkey (Bursa and Bolu) on a human keratinocyte (HaCaT) cell line was investigated. The water from Bursa was thermomineral, while the water from Bolu was oligomineral. HaCaT cells were incubated for 3 days with thermal waters; RNA isolation was carried out in the treated and untreated cells. Studies showed that the tested thermal waters significantly decreased the expression of IL-1α. For thermomineral water, the inhibition was 93%; for oligomineral water, it was 38%. Moreover, thermal waters downregulated the expression of TNFα (59% thermomineral water and 23% oligomineral water) and VEGF (98% thermomineral water and 15% oligomineral water). The observed decrease in the gene expression of TNFα and IL1α could be interpreted as an anti-inflammatory effect of mineral waters on HaCaT cells. Additionally, the suppressed VEGF expression might be an indicator of the antiangiogenic effect on human keratinocytes (Table 5) [126].

The studies were conducted on 50 volunteers to analyze the effect of sulfurous thermal water on the release of anti-inflammatory cytokines. Specific sulfur thermal water was used for the treatments, characterized by additional ions such as chloride, bromine, and sodium iodine. For 12 days, the research group performed one or more of the following treatments: aerosol, inhalations, micronized shower, and humage. The results indicated a greater release of the strong anti-inflammatory cytokine IL-10. In addition, higher levels of IL-10 were also observed in the saliva of patients after treatment with sulfurous thermal water, and this increase correlated positively with the activity of salivary catalase (Table 5) [127].

4.3.2. Antioxidant Activity

Studies were performed to investigate the effects of long-term exposure to sulfur sources on oxidative stress and antioxidant biomarker responses in people living near sulfur sources. The studied area was Al-Hammah sulfurous springs, which are located in the northern part of the Jordan Rift Valley and host many sulfurous springs. The study involved 250 people aged 18 to 45 who did not have hypertension, diabetes problems, or chronic diseases and were not taking any medications. The control group samples were collected from 250 volunteers living in the Der-Allah region, which has a similar mean sea level (MSL) and geographic features but without sulfurous springs exposure. The study group did not experience headaches, nausea, or breathing problems. Moreover, the studies showed that the study group had lower values of total oxidative stress (TOS) and oxidative stress index (OSI) than in the control group. Total antioxidant capacity (TAC) and total nitric oxide (NOX) levels were higher in sulfur spring residents compared to controls. There was also no effect of living near sulfur springs on the level of oxygen saturation (SPO₂) or heart rate. The studies indicated that exposure to sulfur sources increases antioxidant capacity and reduces the level of oxidative stress (Table 5) [128].

Studies were carried out on a group of patients to evaluate sulfur baths on oxidative stress. The experimental group consisted of 19 people who used sulfur baths for 3 weeks. Diagnostic tests were performed before the start of therapy and after completion. Compared to the control group, the studies confirmed a reduction in peroxide concentrations and SOD activities (Table 5) [129].

Braga et al. conducted tests on the antigenotoxicity of sulfurous water. The studies were performed using single-cell alkaline gel electrophoresis (SCGE) (comet assay). DNA damage was significantly inhibited by natural water with H₂S concentrations of 5.0 and 2.5 μg/mL (Table 5) [130].

4.3.3. Antimicrobial Activity

It was shown that hydrogen sulfide in thermal spring waters has the inhibition properties on bacterial proliferation. In sulfurous water containing sodium chloride, bromine, and iodine, the reduction in a value of colony-forming units was 22% for E. coli, 67% for E. faecalis, and 99% for S. aureus. In sulfurous thermal water, the reduction was similar for selected bacterial species. It was presented that the addition of H₂S to waters is able to decrease E. coli to zero after 24 h (Table 5) [131]. Thus, it can be suggested that waters with H₂S have beneficial bacteriostatic activity in local treatments [132].

4.4. Dermatological and Cosmetological Uses of Water

Sulfur waters are one of the types of medical waters with traditional uses and great potential in dermatological and cosmetic applications. The skin is a storehouse of sulfur, which is well absorbed by it. Studies have shown that sulfur waters have a beneficial effect on skin problems such as psoriasis, atopic dermatitis, and acne [117,118,119,120]. In addition, sulfur waters regenerate skin and reduce irritation and swelling caused by varicose veins and have an antioxidant effect, which is important in the care of skin with signs of aging (

Table 6. Directions and general mechanisms of potential cosmetic application of sulfurous water.

Activity	Mechanism of Action	References
Anti-acne activity	-reduction in the growth (65%) of C. acnes	[133]
Effect on psoriasis	-reduction in paw swelling -increases somatostatin concentration -decreases PASI (Psoriasis Area and Severity Index) -increases migration of Langerhans cells from the dermis to the epidermis	[117]
	-reduction in proliferation of keratinocytes, fibroblasts, and macrophages	[134]
	-50% reduction in the PASI score
Effect on atopic dermatitis	-decreases IgE level -inhibition of serum inflammatory cytokines (IL-1β, IL-13, and TNF-α) -reduction in reactive oxygen species (ROS) and malondialdehyde (MDA) in serum	[118]
Effect on skin irritations	-reduction in the degree of skin barrier disruption	[119]
Skin-regenerating effect	-increases the proliferation and migration of keratinocytes -modulating the regenerated collagen and elastic fibers	[120]

) [128,129,130].

4.4.1. Acne

Portuguese Natural Mineral Waters (NMWs) were tested to analyze their antimicrobial properties against strains causing skin pathogens such as Staphylococcus aureus, Escherichia coli, Corynebacterium amycolatum, Candida albicans, Staphylococcus epidermidis, and Cutibacterium acnes. The study used microdilution methods. Mineral waters from 16 active thermal centers were tested. Due to differences in the content of ingredients, they showed various abilities to inhibit microorganisms. Cutibacterium acnes showed a particularly high susceptibility to all Portuguese Natural Mineral Waters belonging to the sulfurous/bicarbonated/sodic ionic profile, exhibiting microbial reductions up to 65% (Table 6) [133].

4.4.2. Psoriasis

The effects of sulfurous medicinal water were tested both in murine dermatitis models and in psoriatic patients. To investigate the anti-inflammatory effect, paw dermatitis was induced by oxazolone in mice. Then, the mice were bathed in the tested and disinfected water for control purposes. The baths lasted 20 min a day and were performed for 2 weeks. Studies on mice showed a reduction in paw swelling after bathing in sulfurous medicinal water. Myeloperoxidase and TNF-α (tumor necrosis factor-α) levels were also analyzed and histological examinations of the skin were performed. The measured parameters did not change. Only an increase in somatostatin concentration in plasma was demonstrated. In a clinical study, 19 patients with psoriasis were bathed for 21 days (2 × 25 min/day). These studies showed that PASI (Psoriasis Area and Severity Index) decreased after the use of therapeutic baths. Additionally, an increase in somatostatin in plasma and a greater migration of Langerhans cells from the dermis to the epidermis were demonstrated. These studies showed that somatostatin released by H₂S plays a role in the mechanism of action of sulfurous medicinal water (Table 6) [135].

Portuguese Natural Mineral Water collected in Monfortinho Thermal Center (rich in silica) was tested to analyze its impact on skin cell homeostasis using two representative cell lines of the epidermis and dermis, keratinocytes and fibroblasts, as well as macrophages, respectively. Mouse skin fibroblasts, macrophages, and human keratinocytes were exposed to a culture medium prepared with Natural Mineral Water. Studies showed a reduction in cellular metabolism in all cell lines tested. The proliferation of keratinocytes, fibroblasts, and macrophages was reduced. This action can be used for hyperkeratotic conditions occurring, among others, in psoriasis or atopic dermatitis (Table 6) [134].

A pilot study was carried out on the effect of sulfurous mineral waters’ application on psoriatic lesions. The study lasted a month and a half and involved 39 patients who were divided into control and experimental groups. The patients applied the water on the affected areas of their skin at home by themselves using a spray. Assessment was performed by a physician and a psychologist trained with PASI and DLQI at days 1, 8, and 15 of the treatment. The research showed that in the study group 21% achieved a 50% reduction in the PASI score (PASI 50) and in the control group, about 17% (Table 6) [117].

4.4.3. Atopic Dermatitis

Bajgai et al. [118] conducted research on the bathing effect of high-concentration mineral spring water (HMW) on redox balance and immune modulation in 2,4-dinitrochlorobenzene (DNCB)-induced atopic dermatitis-like inflammation in hairless mice. Atopic dermatitis-like inflammation was induced on the dorsal skin of female skh-1 hairless mice by the application of DNCB. The mice were treated with 100% pure HMW (PHMW) and 10% diluted HMW (DHMW) through bathing once a day for 4 weeks. Tacrolimus ointment (0.1%) was used as a positive control (PC) and only DNCB treatment as a negative control (NeC) group. The studies showed that HMW reduced scratching behavior in the PHMW and DHMW groups at week 2 and in the PHMW group at week 4 compared to the NeC group. Moreover, the analysis of IgE levels showed its reduction in serum in the DHMW group. Studies showed the inhibition of serum inflammatory cytokines such as interleukin (IL)-1β, IL-13, and tumor necrosis factor-α by PHMW and DHMW. Additionally, in the group treated with PHMW, the level of total reactive oxygen species (ROS) and malondialdehyde (MDA) in serum was significantly reduced. In contrast, glutathione peroxidase (GPx) activity was significantly increased in PHMW (Table 6) [136].

4.4.4. Skin Irritations

Studies were carried out on the effect of São Pedro do Sul (SPS) thermal water on skin irritations. The tests were performed on 17 healthy Caucasian volunteers in whom skin irritation was caused by sodium lauryl sulphate at 2% in two places. Afterwards, purified water or São Pedro do Sul (SPS) thermal water was applied to the irritated skin sites, which were kept under occlusion for 48 h also with Finn chambers. TEWL (transepidermal water loss) was measured to evaluate an anti-irritation effect as an assessment of skin barrier function. A reduction in the degree of skin barrier disruption was observed in 82.4% of respondents compared to purified water alone (Table 6) [119].

4.4.5. Wounds

The effect of hypotonic, bicarbonate-calcium-magnesium mineral water (Comano thermal water) on skin regeneration was examined. The study was performed on 22 animal (New Zealand white rabbit) wound models. Dressings soaked in Comano thermal water improved skin regeneration by increasing the proliferation and migration of keratinocytes but also by positively modulating the regenerated collagen and elastic fibers in the dermis (Table 6) [120].

4.5. Sulphurous Waters in Cosmetics

Sulfurous water is often found in cosmetics produced by health resorts specializing in sulfur baths. They occur in places with rich natural sulfurous water resources. Cosmetics with this water can be used on the face, body, and hair. They are available in the form of serum, creams, emulsions, gels, shampoos, and conditioners. Sulfurous water is used in cosmetics that enhance the skin barrier, moisturization, regeneration, and anti-aging as well as in anti-acne and oily scalp cosmetics due to its antibacterial properties [134]. Examples of cosmetics with sulfurous water are presented in

Table 7. Examples of cosmetic products containing sulfurous waters.

Producer	Country of Origin	Trade Name	Cosmetic Form	Properties of the Cosmetic According to the Producer	Ref.
BALNEO kosmetyki	Poland	Biosulfide vitamin and nourishing face cream	cream	-reduces and smoothes wrinkles -strengthens and improves skin density -rejuvenates features and improves facial contours	[137]
Dr Duda	Poland	Biosulfide mist for face and body	mist	-enhances the protective barrier of the epidermis	[69]
		Biosulfide emulsion gel	fat-free emulsion	-moisturizes and nourishes all skin types -reduces sweating of feet and hands -regenerates damaged nail plate
		Biosulfide Shampoo + KERATIN, PENTAVITIN complex	shampoo	-increases the hydration of hair and scalp -relieves itching
		Buski Sulfur Cream	cream	-moisturizes dry and very dry skin -softens, smoothes, firms, and elasticizes the skin
		Sulfur mask for body care	mask	-removes dead cells from the skin surface (peeling) -facilitates the natural regeneration of dry and cracked skin on heels, elbows, and feet -reduces or removes stretch marks and cellulite -firms, smoothes, and tightens the skin
SPA Cottage	Great Britain	Serum Sulphur Water	serum	-increases collagen production -regenerates the skin	[136]
		Night Cream Sulphur Water	cream	-increases collagen production -regenerates the skin
		Day Cream Sulphur Water	cream	-increases collagen production -regenerates the skin
SULPHUR Busko Zdroj	Poland	Buskie SPA Siarczkowe	bath emulsion	-smoothes -cleanses and moisturizes -reduces tension and relaxes leg heaviness	[77]
		Buska maska siarczkowa/Busko sulphide mask	mask	-smoothes and moisturizes the skin -reduces the visibility of stretch marks -reduces cellulite
		Hypoallergenic sulfide gel	gel	-reduces the number of microorganisms responsible for skin inflammation -regulates the process of exfoliation of the epidermis
		Mineral sulphide cream with vitamin A—for face and body	cream	-moisturizes, smoothes, firms, and elasticizes the skin
		Mineral SPA Shampoo	shampoo	-cleanses the scalp -reduces hair oiliness and reduces the symptoms of dandruff
		Mineral SPA Conditioner	conditioner	-reduces hair oiliness
WIENIEC ZDROJ	Poland	Anti-cellulite body scrub with sulphide water	scrub	-refreshes and exfoliates dead skin -reduces cellulite -eliminates roughness	[138]
		Nourishing and regenerating face serum with sulphide water	serum	-nourishes and reduces skin dryness
		Moisturizing hair conditioner with sulphide water	conditioner	-moisturizes, nourishes, and supports hair regeneration
		Nourishing and moisturizing body balm with sulphide water	balm	-moisturizes, nourishes, and reduces the roughness of the epidermis

. According to INCI, sulfurous water is listed in cosmetics as aqua. This makes it difficult to search for such cosmetics according to their composition. The cosmetics included in Table 7 were searched for in terms of the declaration on the cosmetic that sulfurous water was included as an active ingredient.

5. Potential Cosmetic Combination with Sulfurous Water and Peat

Peat and sulfurous water have been used in natural medicine and cosmetics for centuries. Due to their scientifically proven cosmetic properties, they are used as active ingredients in cosmetics. Medical resorts, sanatoriums, and spas use both raw materials in therapies such as baths, compresses, etc. First of all, such therapies are used in Polish centers that have natural sources of these raw materials, such as Busko Zdroj, Solec Zdroj, and Wieniec Zdroj. These centers often offer combined therapies. In addition, these centers often offer spa cosmetics. The main ingredients of these cosmetics are peat or sulfurous water. Usually, cosmetic lines are created for various skin problems in which these raw materials appear separately. Currently, we can find the Polish company Balneokosmetyki [137], where peat is used together with sulfurous water in products for the care of oily, combination, and acne skin, such as a cream, cleansing gel, and cleansing and smoothing mask. Due to the beneficial potential of cosmetics with these two raw materials, there are grounds to undertake future research on sulfurous water and peat used together.

6. Conclusions

The development of the cosmetics industry and the growing demands placed on cosmetics mean that the effectiveness of cosmetic ingredients must be supported by reliable scientific research. Peloids and medicinal waters used in cosmetics and spa treatments are part of the trend of using safe, natural, and extensively tested raw materials. Both peat and sulfurous waters have been used in medicine for decades, but they are increasingly used in cosmetology, especially in countries where they are common and with an established balneological tradition. More and more often, humic substances are used as raw materials for the production of cosmetics, and not only peat extracts, the composition of which may depend on the source of the raw material. Also, in the case of sulfurous waters, great emphasis is placed on the action of hydrogen sulfide as the main active ingredient. Both peat and sulfurous waters are valuable cosmetic raw materials. The literature data indicate that peat and sulfurous water exhibit anti-inflammatory, antimicrobial, antioxidant, and anti-free radical properties. However, further in vitro and in vivo studies are needed to confirm their efficacy and potential for use in skin health prevention and therapy. The gap in this respect can be particularly seen in relation to peat and humic compounds. The results of in vitro studies using cell models or skin equivalents, as well as in vivo studies using modern measuring equipment on a group of probands, appropriately selected in terms of skin type and possible skin problems, will certainly be important not only for scientists but also for consumers and pharmaceutical and cosmetic companies. The results of the research will not only provide new knowledge about peat and sulfurous waters but also point to directions for their use in cosmetology and dermatology.