Thermal Spring Waters as Cosmeceuticals: An Update

Abstract

Thermal spring waters (TSWs) have long been used in dermatology for chronic inflammatory dermatoses and sensitive skin and are increasingly positioned as cosmeceutical active ingredients. This review summarizes studies on the use of TSW and their hydrobiome derivatives in dermocosmetics and cosmeceuticals for skin health. TSW exhibits anti-inflammatory, antioxidant, soothing, hydrating and barrier-restoring effects in vitro, ex vivo and in clinical studies, improving conditions such as atopic dermatitis, psoriasis, acne, sensitive skin, radiation dermatitis and post-procedure erythema. In parallel, the hydrobiome of TSW has enabled the development of postbiotic and paraprobiotic ingredients, which modulate skin immunity, microbiota, barrier function and clinical signs of inflammatory and sensitive skin. Despite robust preclinical and growing clinical evidence, cosmeceuticals remain regulated as cosmetics in most regions, highlighting the need for specific regulatory frameworks and standardized approaches to demonstrate the safety and efficacy of TSW-based cosmeceuticals, as well as defining acceptable claim categories and minimum evidence thresholds.

1. Introduction

Thermal spring waters (TSWs) have been used since time immemorial in skin care, both for dermatological disorders (psoriasis, dermatitis, rosacea, etc.) and for the improvement of certain skin conditions, such as sensitive skin or to repair the skin barrier. Although other mechanisms may be involved, some recent reviews emphasize the chemical effects of TSW.

Cacciapuoti et al. [1] described the use of thermal spring waters in the management of chronic skin diseases, highlighting the effects of sulfate, sulfurous, bicarbonate, carbonate, iodine-bromo-saline waters, especially those rich in magnesium, calcium, manganese, iron and zinc, with moisturizing, regenerating and antioxidant effects, among others. Protano et al. [2] conducted a systematic review to evaluate the effects of balneotherapy using thermal mineral water baths in the management of dermatological diseases, finding that most of the studies are related to psoriasis and atopic dermatitis (AD), with the chemical profile of the waters similar to those previously described by Cacciapuoti et al. [1].

The role of minerals and trace elements in skin health was the aim of a recent review, which details the effects of the predominant anions and cations in thermal waters, but also the role of trace elements, such as strontium, manganese, boron, zinc, etc., often forgotten, as well as other better-known compounds such as SiO₂ and CO₂. The specific effects were summarized as anti-inflammatory, antioxidant, wound healing improvement, skin hydration, and skin barrier recovery activities [3].

The presence of natural organic matter and organic compounds present in certain TSWs should also be considered, as it has been suggested to contribute to their healing properties [4].

Recently, there has also been interest in the role of the hydrobiome of thermal waters in their effects on the skin. Some studies show that they can regulate the skin microbiota involved in dermatological disorders [5,6,7,8,9], and, in light of this, cosmetic companies have begun to market derivative products [10,11] or TSW itself to improve and balance the skin microbiota [11,12]. One example is dermocosmetic products that include fermented products, lysates, etc., of the microorganisms present in thermal waters, which have been shown to be able to improve certain skin conditions and dermatological illnesses such as rosacea, acne, AD, seborrheic dermatitis and psoriasis, among others [12,13].

Although the effects of thermal waters have been classically attributed to the thermotherapeutic action and the chemical elements present, they have recently been linked to a hormetic mechanism, in which neuroendocrine and immunological effects seem to be decisive [13,14].

Despite the term “cosmeceutical” being originally created by Mr. R.E Reed in 1962, as President of the Society of Cosmetic Chemists [14], it was Albert Kligman of the University of Pennsylvania who popularized this concept, that is, used it to describe a hybrid category of products halfway between cosmetics and pharmaceuticals. The definition of cosmeceuticals is as follows: “a cosmetic product that is supposed to have a therapeutic action capable of positively affecting the skin beyond the moment of its application” [15]. Cosmeceuticals have also been defined as “cosmetics that have active ingredients similar to a pharmaceutical product but in reduced concentrations of active ingredients”, which are sold over-the-counter but have profound effects on skin appearance and functioning [16].

Cosmeceuticals typically contain at least one distinctive ingredient and promise beneficial effects beyond the capabilities of purely cosmetic products; they claim to improve skin function, texture, tone, radiance, or firmness [17]. Despite that, they are not classified as drugs and are regulated by the same rules as cosmetics. Therefore, in Europe, until there is no specific legislation for cosmeceuticals, the so-called “borderline products” are carefully evaluated and the decision on a product’s classification (when it is unclear whether a particular product is a cosmetic product under cosmetics legislation or whether it falls under other sectorial legislation) must be taken on a case-by-case basis (https://single-market-economy.ec.europa.eu/sectors/cosmetics/cosmetic-products-specific-topics/borderline-products_en (accessed on 20 January 2026).

In Japan, there are regulations for skin care products that are not considered pure medicines or pure cosmetics in the traditional sense, but rather a mixture of both, and are called “quasi-drugs.” They allow cosmetics to contain pharmacologically active ingredients, as long as the medicinal effects are mild and the safety of the products has been proven [18].

Table 1. Specific regulations for cosmeceuticals in Europe, USA, Japan, and Korea.

Country/Regulation	Comments	Web Page
EU: Regulation (EC) No 1223/2009	No regulations related to cosmeceuticals, only for cosmetics	http://data.europa.eu/eli/reg/2009/1223/oj (accessed on 4 March 2026).
EU: Borderline products guide	Guide to assess on a case-by-case basis	https://single-market-economy.ec.europa.eu/document/download/cebfe674-c737-4ec2-b536-c86e777c4b69_en (accessed on 4 March 2026).
USA: OTC Guidelines	FDA registrations for OTC products 1	https://www.federalregister.gov/documents/2022/06/28/2022-13309/nonprescription-drug-product-with-an-additional-condition-for-nonprescription-use (accessed on 4 March 2026).
Korea: Quasi-Drug Regulation	Quasi-drugs information and guidelines	https://www.mfds.go.kr/eng/wpge/m_25/de011015l001.do (accessed on 4 March 2026).
Japan: Quasi-Drug Regulation	Act on Securing Quality, Efficacy and Safety of Products, Including Pharmaceuticals and Medical Devices	https://www.japaneselawtranslation.go.jp/en/laws/view/3213/en (accessed on 4 March 2026).

¹ OTC: Over the counter.

shows some examples of the specific regulations for cosmeceuticals (Europe, USA, Japan, and Korea).

In this scenario, regulation for cosmeceuticals is necessary so that their use and marketing is comparable to quasi-drugs, as well as a guide to assess their safety and efficacy. While the possible regulation is not moving forward, commercial companies, especially those of TSW cosmetics, use this concept and name as a claim to an action on the skin beyond the purely cosmetic.

2. Materials and Methods

The aim of this work is to review the latest investigations that can shed light on this matter.

For this review, PubMed, Web of Science, SciFinder, Google Scholar, and Scopus databases were reviewed. The search terms used were “thermal spring waters and skin”, “microbiome and thermal waters”, “skin microbiome”, combined with “cosmetics” or “cosmeceuticals” or “dermocosmetics”.

To ensure that relevant information was obtained to answer the research question, inclusion and exclusion criteria were established. The inclusion criteria were articles focusing on the problem under study and articles describing clinical studies related to cosmetic formulations prepared with TSW, both with natural TSW or its derivatives (hydrobiome). As an exclusion criterion, articles not related to the problem under study and in which thermal water was not one of the active ingredients of the formulation were considered.

The research included all the articles published up to 31 December 2025.

3. Thermal Spring Waters as Active Ingredients

TSW could act as active ingredients in cosmeceuticals, being used directly and provided in sprays or incorporated in cosmetic formulations (e.g., gels and creams), as presented in

Table 2. Cosmeceutical formulations prepared with TSW: main chemical elements of TSW, specific activities and cosmeceutical potential uses.

TSW	Chemical(s) of Major Role	Cosmeceutical Formulation	Specific Activities	Potential Cosmeceutical Uses	Reference
Avéne	Bicarbonate, Calcium, Magnesium	Spray	Anti-inflammatory effects Antioxidant properties Improvement of epidermal barrier function Decreasing post-chemical peeling redness	Acne AD Psoriasis Post photodynamic therapy Post-chemical peeling intervention Dermal melasma Post-chemical peeling	[19,20,21,22,23,24,25,26,27,28]
		Spray + standardized emollient	Improvement in symptoms of atopic dermatitis (scaling, itching, pruritus, and erythema)	AD	[29]
		Gel	Improvement of QoL and radiation dermatitis signs	Skin post-oncological recovery	[30]
		Cream	Improvement of QoL	Contact dermatitis Climatic dermatitis	[31]
Blue Lagoon	Silica	Galenic formulation (algae extracts and silica mud)	Improvement of the skin barrier and protection against extrinsic skin aging	Dry skin	[32]
		Serum	Decrease in the number of pigment spots	Hyperpigmentation	[33]
Chaves	Sulfur, Silicon, Sodium	Spray	TEWL reduction	Dry skin	[34]
Cró (PT)	Sodium, Silica, Calcium, Potassium, Sulphur	Gel	Hydration properties, TEWL reduction and skin relief improvement	Skin maintenance and barrier effect improvement	[35]
Dead Sea (IL)	Magnesium, Calcium, Sodium, Potassium, Zin, Strontium	Cream (DermudTM)	Antioxidant and anti-inflammatory properties Protection against ultraviolet B-induced stress	Sunscreen Sensitive skin	[36]
		Creams (Clineral Topic™ and DermudTM)	Improvement of OSAAD score Hydration properties	AD	[37]
Jonzac (FR)	Sulphate, Chloride, Sodium, Calcium	Spray	Hydration properties Soothing effect	Normal skin	[38]
La Roche-Posay (FR)	Selenium	Gel	Anti-inflammatory properties	Sensitive skin	[39]
		Cream	Protection against UVB-induced skin damage in humans	Sunscreen Skin barrier repair
Monfortinho (PT)	Silica	Cream	Antiproliferative effect Anti-inflammatory properties	Psoriasis and Eczema	[40]
Uriage (FR)	Zinc	Cream	Antioxidant activity and UVB-induced DNA damage protection	Aging Sunscreen	[41]
Vichy (FR)	Boron, Manganese	Spray	Anti-inflammatory properties	Sensitive skin	[42]
		Spray	Epidermal regeneration	Wound healing	[43]
		Spray	Hydration properties TEWL reduction	Dry skin	[43]
		Spray	Hydration properties Decrease TEWL Anti-inflammatory properties	Sensitive skin	[43]
		Gel	Protective effect against UV damage	Sunscreen	[43]

AD: atopic dermatitis. OSAAD: objective severity assessment of atopic dermatitis. QoL: quality of life. TEWL: transepidermal water loss. UV: ultraviolet.

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TSWs are very well-known for their cosmetic properties, mainly related to their moisturizing, soothing, and protective effects against external agents. The main research has been carried out by cosmetic brands that market these types of skin care products, with French companies generating the most scientific studies. Recently, Kanwal et al. reviewed the latest evidence, resulting in both in vitro and in vivo studies that validated the anti-inflammatory, immunomodulatory, and antioxidant potential of TSW in dermatology. Furthermore, TSWs have been shown to be beneficial for treating various skin conditions and enhancing cosmeceutical effects, and the studies have strongly demonstrated the therapeutic benefits of different thermal waters for the successful treatment of many skin diseases; thus, TSWs have been incorporated into cosmetics and cosmeceuticals for skin hydration and anti-aging and anti-wrinkle effects [44]. Additionally, Figueiredo et al. revised the use of TWS as an active ingredient in cosmetic formulations, concluding that it could be used as an adjuvant or in the treatment of various skin disorders, emphasizing the moisturizing, soothing, antioxidant, anti-inflammatory, and skin barrier repair properties demonstrated in in vitro studies and clinical trials, with the absence of side effects [45].

One of the most studied thermal waters is Avène TSW, with the studies carried out by the company/brand itself, sometimes in collaboration with universities or research centers. The first studies date back to the 1990s, and subsequent in vitro, ex vivo, and in vivo studies were published, demonstrating its anti-inflammatory and antioxidant properties. In recent years, the biological fraction of these waters has also been investigated, and studies have been published on the potential applications of extracts and lysates of the microorganisms present in them (see Section 4).

Several in vitro studies showed that Avène TSW exhibited anti-inflammatory properties [19,20,21,22,23], attributed to its low mineralization and the presence of bicarbonate anion, calcium and magnesium cations, and also the presence of zinc as a trace element. Clinical studies confirmed the initial findings. Thus, Avène TSW was used as an adjunctive therapy in skin care following photodynamic therapy. Comparative studies included 25 patients with acne vulgaris or photodamage, with or without actinic keratosis, and 20 patients with bilateral dermal melasma. In both studies, Avène TSW exerted anti-inflammatory activity, reducing erythema and pruritus and relieving pain. These studies demonstrated that spraying Avène TSW after photodynamic therapy significantly reduces the short-term adverse effects associated with the procedure. The results demonstrated the soothing and anti-irritant properties of Avène TSW [24,25]. Additionally, Casas et al. conducted a study of clinical and inflammatory biomarkers in two groups of patients with AD and psoriasis, treated with various therapeutic techniques, including spraying with Avène TSW. The results showed a decrease in both the SCORing Atopic Dermatitis (SCORAD) and the Psoriasis Area Severity Index (PASI), associated with a significant reduction in IL-8 and Staphylococcus aureus colonization [26]. Finally, an ex vivo and clinical study conducted by Mias et al. showed that Avène TSW is able to decrease redness and reduce the overall sensitivity scale after a dermatological chemical peeling [27]. Later, Mias et al. also investigated and compared the effect of two TSW types: Avène TSW and a mineral-rich TSW on post-chemical peeling redness. Avene TSW significantly decreased post-peeling redness, while MR-TSW increased it. The overall sensitivity scale of consumers decreased by 47% using Avene TSW for 7 days. The authors suggested that differences in biomechanical effects could be linked to differences in calcium content of the TSW, being more effective in low-mineral-content TSW [28].

Studies on AD are also of interest; for example, Avène TSW was applied twice daily ad libitum for 21 days to the randomized arm, and a standardized emollient was applied to the entire body, including both arms, for the same 21 days. Results showed an improvement in symptoms of atopic dermatitis (scaling, itching, pruritus, and erythema) versus emollient alone [29].

Although AD, psoriasis, and certain acne types need pharmacological therapy, the use of specific cosmeceuticals can ameliorate symptoms, e.g., scaling and itching on AD and psoriasis, or reduce inflammation in acne. Additionally, TSW cosmeceuticals can improve skin hydration and strengthen the skin barrier, which is damaged in this type of dermatological disease [46].

Another study compared a gel formulated with TSW with a trolamine cream; in an open-label multicenter comparative study, Avène TSW cream or trolamine was applied five times for ten weeks on the skin of patients with radiation dermatitis due to cancer therapy. Results showed that Avène TSW gel was similar to the control product in the prophylaxis of radiation dermatitis. Tolerance was better and the pruritus was significantly more delayed in patients who applied the Avène TSW gel than in controls [30].

In an open-label study, the efficacy and reparative effect of a dermocosmetic product on subjects suffering from hand eczema was assessed. After 7 and 21 days of daily application, an improvement in quality of life (QoL) was found, and both physicians and subjects noticed a significant improvement in hand eczema symptoms starting at 7 days after the first application, concluding that the formula can ameliorate contact dermatitis and climatic dermatitis [31].

An ex vivo study performed by Mias et al. investigated the biomechanical barrier properties of the skin, observing that Avène TSW showed a specific compaction of the skin layers, characterized by an increase in the total number of external skin layers, compared to non-treated samples and controls. So, the authors concluded that treatment with Avène TSW can strengthen skin barrier function [28].

Blue Lagoon TSW, a highly mineralized water with an extremely high concentration of silica, demonstrated its therapeutic effect in psoriasis [47,48,49,50,51]. An in vivo study with a galenic formulation composed of two algae extracts (coccoid and filamentous algae) and an extract from silica mud was performed. The skin of the volunteers was irradiated with a single dose of UVA radiation (100 J/cm²) and then the galenic formula was applied once daily for a total of four weeks. A significant increase in the mRNA expression of involucrin, filaggrin, and transglutaminase-1 was observed. Furthermore, topical application of Blue Lagoon extracts also induced the mRNA expression of collagen 1A1 and 1A2 in non-irradiated skin after four weeks of treatment. A significant increase in the mRNA expression of matrix metalloproteinase-1, IL-1, and IL-6 was also observed in untreated skin areas. In stark contrast, UV-induced gene expression was significantly reduced in contralateral skin areas treated with Blue Lagoon extracts prior to exposure. The results suggest that silica mud and these two species of algae from Blue Lagoon contain biologically active material that can be used to improve the skin barrier and protect against extrinsic skin aging, although further studies are needed to identify the specific biological compounds involved in these effects [32].

Other studies focused on the effects of the exopolysaccharides (EPSs) secreted by Cyanobacterium aponinum (EPS-Ca), a prevalent organism in the Blue Lagoon, finding that EPSs could contribute to reducing PASI on psoriasis, as has been shown to decrease the levels of some interleukins, as IL-17, IL-13 and IL-10 [52,53].

Additionally, the effects of Blue Lagoon algae extract on skin pigmentation were investigated using in vitro and in vivo studies. An in vitro study investigated gene expression in epidermal melanocytes, followed by an in vivo study with volunteers suffering from skin pigmentation disorders. In the in vitro study, the expression of melanocyte-stimulating hormone (MSH)-induced mRNAs in epidermal melanocytes treated with Blue Lagoon algae extracts was analyzed. A significant reduction in MSH-induced expression of genes essential for melanin synthesis, such as tyrosinase, tyrosinase-related protein 1, dopachrome tautomerase, melan A protein, and premelanosome protein, was observed. In parallel, an in vivo study was conducted with 60 volunteers with facial hyperpigmentation, who were treated twice daily with a serum containing Blue Lagoon algae, with the vehicle of the cosmetic formula serving as the control. The results showed that the constitutive pigmentation of the skin, determined by colorimetry (individual typology angle and luminescence), did not differ significantly between the two treatments (serum vs. vehicle). In stark contrast, digital photography with cross-polarized illumination and RBX technology (VISIA CR) revealed that the number of pigment spots on the face treated with the serum decreased significantly compared to the face treated with the vehicle [33].

Chaves TSW, sulfur, silicon and sodium-rich water, was also investigated. In vitro experiments demonstrated its anti-inflammatory properties, and in vivo research revealed that Chaves TSW improved the integrity of the skin barrier and preserved the skin microbial community. The antioxidant capacity and the production of collagen and fibronectin have also been investigated, in addition to changes in the microbiota. Although no evidence of antioxidant and anti-aging power was found, measurements of biometric properties yielded interesting results. The most remarkable characteristic of Chaves TSW is its anti-inflammatory properties, as it has been shown to significantly reduce IL-6 levels in HaCaT cells exposed to urban pollution. This makes it relevant in the context of the increasing environmental stressors (the so-called exposome) that affect skin health. Regarding changes in the microbiota before and after the application of Chaves TSW (0 and day 16), results showed that the relative abundances of S. epidermidis and P. acnes were not statistically significant, and the relative abundance of the Malassezia genus was similarly detected at both time points. Furthermore, the clinical study revealed a significant reduction in TEWL in human volunteers, suggesting that Chaves TSW could help restore the skin barrier function. This is of great interest in the care of skin conditions such as eczema and certain dermatoses where the barrier function is impaired [34], but additional clinical investigations are needed.

Comano TSW, a bicarbonate-, calcium- and magnesium-rich spring water, was widely studied both in vitro and in vivo in psoriatic patients, and also in eczematous dermatitis and AD patients [54,55,56,57], concluding that Comano TSW exposure significantly down-regulated the intracellular levels of TNF-α and also reduced the intracellular levels and secretion rates of IL-8 [57]. Later on, ex vivo studies in a skin experimental wound-healing model were performed to investigate the regenerative effect of several lysates obtained by microbiota of Comano TSW: lysate 1 (L1)—closest relative Rudaea cellulosilytica, phylum Proteobacteria; lysate 2 (L2)—closest relative Mesorhizobium erdmanii, phylum Proteobacteria; lysate 3 (L3)—closest relative Herbiconiux ginseng, phylum Actinobacteria; and lysate 4 (L4)—closest relative Fictibacillus phosphorivorans, phylum Firmicutes, observing a complete restoration of all the skin layers, and their features were the closest to the normal skin in lysate 2 [5]. However, to the best of our knowledge, no specific in vivo and/or clinical research has been published on cosmeceutical formulations prepared with Comano TSW, despite some patents related to this thermal water being available (see Section 5).

Crò TSW, a sulfurous, sodium, silica, calcium, and potassium-rich spring water, has proven effective in maintaining skin hydration and barrier function. Nunes et al. [35]. developed a dermocosmetic hydrophilic gel containing >90% Cró thermal water and compared it with a control gel prepared with purified water. The thermal water demonstrated biocompatibility, supporting normal human dermal fibroblast adhesion and proliferation. The formulation maintained stable organoleptic properties during storage. Compared with the control, the thermal water gel exhibited lower firmness, adhesiveness, and spreadability, characteristics favorable for topical application and potentially enabling sustained release of active compounds. In a clinical study with 20 healthy volunteers, the gel formulation containing thermal water preserved skin physiological pH, a statistically significant increase in hydration, and statistically significant reduced transepidermal water loss (TEWL) after 30 min, suggesting an occlusive effect on barrier function, in comparison with the control gel. Additionally, it improved skin surface parameters, reducing roughness and scaliness while enhancing smoothness. These findings highlight the beneficial role of Cró TSW in dermocosmetic formulations and its potential for managing dermatological conditions [35], despite the small number of volunteers.

Dead Sea TSW is very well-known for its anti-inflammatory properties in AD but also is able to protect against ultraviolet B-induced stress. Some of those studies are explained below.

Meital Portugal-Cohen et al. [35] evaluated the protective effects of DermudTM, a patented leave-on skin emulsion enriched with DS mineral mud, DSW, and other actives, against UVB-induced damage in human skin cultures. UVB exposure reduced mitochondrial activity by 20% and increased caspase-3 activity tenfold, effects that were reversed or markedly reduced by DermudTM pretreatment. The formulation enhanced ferric-reducing antioxidant power (FRAP) by 50% in controls, neutralized UVB-induced ROS, and partially restored uric acid levels. Furthermore, it strongly inhibited the secretion of proinflammatory cytokines (TNF-α, IL-1α, IL-6, IL-8). Overall, DermudTM demonstrated antioxidant, anti-apoptotic, and anti-inflammatory properties, effectively reducing photodamage and photoaging, and therefore demonstrated its potential against UVB-related skin pathologies.

Additionally, the same research group conducted a 12-week double-blind study on 86 children with mild-to-moderate AD to assess an emollient cream enriched with Dead Sea minerals. Participants received twice-daily treatment with the mineral-rich cream or two control creams: a lower-concentration mineral and a mineral-free emollient. Both mineral-enriched creams improved objective severity assessment of AD (OSAAD) scores, but only the higher-concentration cream improved TEWL and stratum corneum hydration. This formulation demonstrated the greatest efficacy across skin severity scores, supporting the role of Dead Sea water in improving skin barrier function and its potential as an effective adjuvant in AD management [37].

Jonzac TSW, a sulphate, chloride, sodium and calcium-rich TSW, was studied to test its potential in skin hydration. Stratum corneum hydration was measured directly using a corneometer, finding that, 8 h and 24 h following a unique application of 2 mg per cm² of natural Jonzac TSW, the skin hydration increased with respect to baseline. Furthermore, a formulation gel containing 98.10% Jonzac TSW was applied twice (in the morning and in the evening) on the face of 10 volunteers for 29 days. The analysis of the microrelief by DIAGNOSKIN^® system was realized before, immediately after a unique application of the gel containing Jonzac TSW, and after 30 days of treatment, observing a shooting effect, and an improvement of cutaneous microrelief [38]. Additional research is needed, since the number of volunteers does not allow for relevant statements to be made.

La Roche-Posay TSW also showed anti-inflammatory properties and protection against UVB-induced skin damage in adults. A comparative study with 10 volunteers evaluated the anti-inflammatory effects of La Roche-Posay TSW by applying 0.75% sodium lauryl sulfate (a well-known irritant) under occlusion for 24 h on the forearm, followed by treatment with a gel containing La Roche-Posay TSW or demineralized water. Cutaneous blood flow was reduced by 46% with La Roche-Posay TSW-based gel and 15% with demineralized water, supporting the anti-inflammatory properties of La Roche-Posay TSW [39].

Furthermore, a randomized double-blind study with 10 participants evaluated the photoprotective effects of a cream containing La Roche-Posay TSW against ultraviolet B-induced erythema and formation of sunburn cells. Areas pretreated with the La Roche-Posay TSW cream showed a significant reduction in epidermal sunburn cells per cm² compared to areas treated with a cream containing demineralized water, 24 h after UVB exposure [39]. Neither the LRP-TSW cream nor the demineralized water cream provided significant protection against erythema, and the sample size is too small to draw relevant conclusions.

Vichy TSW is a very high mineral water which contains a particularly high content of calcium, and is also rich in boron, well-known for its role in wound healing, and manganese, which exerts antioxidant activity [58]. Berardesca et al. investigated that the Vichy TSW can exert anti-inflammatory properties. An open study in 20 volunteers evaluated the efficacy of Vichy TSW in repairing irritated skin in comparison with other low mineral content TSW (control TSW). To induce chemical irritation, 3% SLS patches were applied on a delineated area on the forearms of each subject for 16 h. The chemically irritated sites were randomly assigned to receive Vichy TSW or control TSW for 10 days twice daily application or no treatment. Chromameter was used to measure redness, and results showed 20% decrease with Vichy TSW by day 6 after irritation compared to D0 (p < 0.05), and redness was improved by day 6 with control TSW, but there was no statistically significant improvement in redness for the untreated skin until day 8. Recovery of clinically assessed erythema (on a 4-point scale from absent to severe) was observed from day 2 (−20% vs. baseline) for Vichy TSW, while a decrease in erythema score was not statistically significant compared to baseline for control TSW and untreated skin until day 3 and day 6, respectively. Authors concluded that the recovery from redness and erythema was faster following topical application of Vichy TSW compared to control TSW or untreated skin [42].

Several studies were performed by Rasmont et al. to evaluate soothing and hydrating properties of Vichy TSW. Skin hydration and TEWL was assessed using Corneometer (based on the physical principle of capacitance), and Tewameter (on the principle of Fick’s diffusion formula) in a randomized study in 20 Japanese women aged 27–68 years old with oily or combination skin. Subjects apply Vichy VMW twice daily for 3 weeks on an area of about 20 cm² of the left or right cheek and the other side of the face was left untreated. Results showed that after application of Vichy VMW, a significant decrease in TEWL was observed between baseline and week 3, with an 18% decrease compared to the untreated control site. Although there was no statistically significant difference between Vichy TSW and the control, a 9% statistically significant increase in the electrical capacitance (hydration) of the Vichy TSW treated area was observed after 3 weeks compared to the baseline measurements (p = 0.001) [43].

Endogenous catalase activity was also measured in vivo in 24 women of phototype III who applied samples of Vichy TSW, twice daily for 4 days, been untreated skin as a control. The corneocytes were harvested by stripping from the treated and untreated areas, and CAT activity was measured by colorimetric assay. After 4 days of application, Vichy TSW significantly increased catalase activity compared to the reference water and the results showed higher catalase activity with Vichy TSW in 80% of subjects on day 4 compared to 50% on day 1 [43]. Additionally, an in vivo study investigated the efficacy of a Vichy TSW gel formulation in preventing or restoring endogenous catalase activity following exposure to UVA radiation (320–440 nm), which induces an oxidative stress response in the skin. Subjects aged 25–39 years were treated with Vichy TSW gel for 4 days prior to exposure to a single dose of UVA. When untreated skin was exposed to UVA radiation, catalase activity decreased by a statistically significant 70% compared to unexposed control skin. However, when skin was pretreated with Vichy TSW gel prior to UV exposure, catalase activity was maintained, as the resulting catalase activity was not statistically different compared to unexposed control skin. These results suggest a protective biological effect on endogenous catalase activity, which may contribute to skin homeostasis and prevent photo-oxidative stress [43].

A clinical study in 20 Caucasian women (skin phototype I–III) evaluated the effect of Vichy TSW on improving sensitive skin after performing a stinging test. The side of application was randomized, and Vichy TSW was applied on half the face and demineralized water (DM) on the other side of the face, as a control, twice daily for 30 days. Sensitive skin was determined by a stinging test score ≥ 3 [on a scale from 0 (none), 1 (mild), 2 (moderate), to 3 (severe) burning/stinging/itching/painful sensation], and assessments included skin hydration by Corneometer, TEWL by Tewameter, and clinical evaluation of dryness on an 11-point scale (from 0 none to 10 extremely dry). Results showed statistically significant increases in skin hydration after Vichy TSW application at 15 days and 30 days compared to baseline. The decrease in TEWL between baseline and after 30 days of Vichy TSW application was not statistically significant, but statistically significant differences in skin hydration measurements between Vichy TSW vs. DM were observed at both day 15 (p < 0.05) and day 30 (p < 0.01). Moreover, Vichy TSW significantly improved skin dryness after 30 days of application, and statistically significant differences between Vichy TSW and DM for skin dryness were observed after 15 and 30 days of treatment. Additionally, a statistically significant decrease in skin sensitivity was observed between day 0 and after 30 days of twice-daily application of Vichy TSW compared to baseline (p ≤ 0.0001) [43].

Other studies focused on skin regeneration. The effect of Vichy TSW on epidermal cell proliferation in a double-blind study in which 31 women were evaluated by dansyl chloride testing on both forearms for 24 h; skin renewal was assessed by fluorescence measurements after twice daily application of Vichy TSW on one randomly designated forearm. Results showed that epidermal regeneration was increased by 9% after daily application of Vichy TSW, and mean cell turnover time was significantly faster for the Vichy TSW-treated site compared to the untreated control (p = 0.016) [43].

Mineral-medicinal and thermal waters are therefore a natural source of active ingredients for the preparation of cosmeceuticals and personal care products in general, whose proven effects are primarily linked to their content of macro- and microminerals and trace elements. In any case, more independent investigations are needed, since, as mentioned, most of them are linked to cosmetic commercial brands. It should also be noted that much of the evidence relates to the balneotherapy use of thermal waters for various skin conditions, and although this evidence supports research for the development of cosmeceuticals, more clinical studies are needed in which cosmetic formulations are the subject of study.

4. Thermal Spring Waters Hydrobiome Derivatives as Active Ingredients in Cosmeceuticals

In addition to the mineral-medicinal waters themselves, the recent trend is to include, as active ingredients, a wide group of compounds derived from the hydrobiome.

The hydrobiome is defined as “natural microbial community present in waters” [12]. Research on the biodiversity of thermal waters has always been a matter of interest, both for the preservation of the resource and the control of microbiological quality, as well as in the search for bioactive substances of interest for different purposes: pharmacology, technology, food and beverages, cosmetics, etc. Some examples are thermostable lipases from Sulfolobus acidophilus [59], food enzymes (glucoamylases, xylanases) from Thermus aquaticus [60], and other extremozymes (oxidoreductases, hydrolases, lyases, isomerases, etc.) [61]; the very well-known polymerase Taq, also obtained from Thermus aquaticus; or CRISPRi approaches for gene silencing, which were also developed from thermophiles [62], among others.

Thus, in recent years, research into the hydrobiome of thermal waters has led to the development of derivatives of biologically active substances with specific actions in skin care. The number of brands that have advanced in this line is small, but they have opened a window of opportunity for the development of cosmetic and cosmeceutical products that combine thermal water and active ingredients obtained from the hydrobiome, such as extracts, lysates and compounds obtained by fermentation processes.

Due to the trend of including pre-, pro-, syn and postbiotics in dermocosmetic products, these active ingredients are often identified as such, becoming a powerful claim. Before proceeding to review the publications related to cosmeceuticals made from the hydrobiome of thermal waters, we will briefly review the definition of pre-, pro-, syn and postbiotics.

The International Scientific Association for Probiotics and Prebiotics (ISAPP) defined prebiotics as “a substrate that is selectively utilized by host microorganisms conferring a health benefit”. The scientific panel added that prebiotics are usually carbohydrate-based, but other substances, such as polyphenols and polyunsaturated fatty acids converted to respective conjugated fatty acids, might fit the updated definition, assuming a convincing weight of evidence in the target host [63].

In 2014, the ISAPP association defined probiotics as “live microorganisms that, when administered in adequate amounts, confer a health benefit on the host”, and differentiates live microbes used as processing aids or sources of useful compounds from those administered primarily for their health benefits [64].

Later, ISAPP defined synbiotics as “a mixture comprising live microorganisms and substrate(s) selectively utilized by host microorganisms that confers a health benefit on the host”. The panel considered defining synbiotics as simply a mixture of probiotics and prebiotics, but the panel accepted that a functional synbiotic can be formulated in lower doses than those in which the probiotic or prebiotic is administered separately [65].

And, finally, in 2021, the expert panel achieved a consensus on the definition of postbiotics as “preparation of inanimate microorganisms and/or their components that confers a health benefit on the host”. Adding that postbiotics are deliberately inactivated microbial cells with or without metabolites or cell components that contribute to demonstrated health benefits [66].

Additionally, the new concept of paraprobiotics emerged. Cuevas-González et al. [67] revised the concept of postbiotics and paraprobiotics, defined the latter as “inactivated (non-viable) microbial (probiotic or non-probiotic) intact cells, which when administered in sufficient amounts confer benefits to consumers”. Other terms used to identify paraprobiotics are non-viable probiotics, inactivated probiotics, or ghost probiotics [67].

Different methods can be used to obtain postbiotics and paraprobiotics. Postbiotics can be obtained by enzymatic, chemical or heat sonication, and also by high pressure to disrupt the cell structure, and paraprobiotics by heat (thermisation, pasteurization, sterilization), radiation (ionizing and UV rays), high pressure and sonication [67].

Very few cosmetics companies have undertaken projects to identify species of interest in the microbiome of thermal waters, allowing them to develop cosmeceuticals. It should be noted that, due to legal restrictions regarding the microbiological quality of cosmetics, only prebiotics, post- and paraprobiotics can be used as active ingredients, that is, non-viable ones.

Thus, based on the above concepts, the derivatives of the hydrobiome that can be found in cosmeceuticals are postbiotics and paraprobiotics, but also extracts and ferments obtained from microorganisms in thermal waters.

Mourelle et al. (2023) [12] reviewed the main research on the hydrobiome and TSW, summarizing in vitro, in vivo and ex vivo research, as well as clinical studies.

Table 3. TSW hydrobiome derivatives as active ingredients in cosmeceuticals.

TSW	Type of TSW	Hydrobiome Ingredient	Cosmeceutical Formulation and Potential Uses	Reference
Avène (FR)	Bicarbonate Silica- and zinc-rich	Aquaphilus dolomiae extract	Emollient cream Xerosis and sensitive skin	[10]
		Aquaphilus dolomiae extract	Emollient balm Xerosis in cancer patients	[68]
		Aquaphilus dolomiae extract	Cream Several skin conditions (erythema, edema, pruritus)	[69]
Blue Lagoon (ISL)	Sodium Chloride Silica-rich	Cyanobacterium aponinum extract + solution from silica mud	Galenic formulation Reduction TEWL Protection from UV radiation	[32]
		Cyanobacterium aponinum extract	Serum Skin pigmentation disorders	[33]
La Roche-Posay (FR)	Bicarbonate Strontium- and selenium-rich	Vitreoscilla filiformis extract	Ointment AD	[70,71]
		Culture of V. filiformis in La Roche-Posay thermal water	Cream AD	[72]
		Culture of V. filiformis in La Roche-Posay thermal water	Lotion Seborrheic dermatitis	[73]
		Vitreoscilla filiformis lysate	Emollient cream AD Recovery skin barrier	[74]
		Vitreoscilla filiformis lysate	Emollient formulation AD Skin dryness	[75]
Solía (ES)	Bicarbonate Sodium-, calcium- and magnesium-rich	Phaeodactylum tricornutum extract	Cleanser, serum and cream Sensitive skin Anti-aging	[76]
Vichy (FR)	Magnesium-, potassium- and calcium-rich	Vitreoscilla filiformis extract	Cream Stressed skin Anti-aging	[77]
		Vitreoscilla filiformis lysate	Cream Dry skin Sensitive skin Rosacea	[78]

AD: Atopic Dermatitis. TEWL: Transepidermal Water Loss. UV: Ultraviolet.

summarizes the ex vivo and clinical studies related to cosmeceutical formulations based on TSW hydrobiome derivatives, along with more recent ones.

Several studies in vivo and ex vivo were carried out to investigate extracts and lysates obtained from the strain Aquaphilus dolomiae found in Avène TSW, showing anti-inflammatory and antipruritic activities, wound healing properties, as well as strengthening the skin barrier function [10,68,79,80,81,82,83,84,85,86,87]. Avène Laboratoire Dermatologique registered three postbiotic compounds obtained from A. dolomiae, called I-modulia^®, C+-Restore™, and D-Sensinose™. Moreover, recently a real word study evaluated the effectiveness and tolerability of a shooting cream containing a postbiotic from A. dolomiae; the study included 1137 patients suffering from different skin dermatological conditions with several clinical signs (erythema, edema, oozing, and scabs), and symptoms (burning sensations, tingling, tightness, pruritus, and pain), resulting the improvement of the symptoms after a mean time of product use of 6.1 ± 5.0 days [69].

Blue Lagoon microalgae were also investigated, finding that Cyanobacterium aponinum is the dominant member in this microbial ecosystem. Studies in vitro and in vivo showed that the extracts of C. aponinum are able to reduce TEWL [32], as well as uneven skin pigmentation [33]; and the exopolysaccharides secreted by this strain may be involved in the therapeutic results observed in psoriasis patients, exerting anti-inflammatory activity [52,53].

Lysates obtained from different strains isolated from Comano TSW were investigated to test in vitro and ex vivo the wound healing properties of this TSW, showing anti-inflammatory properties [5,88]. These results suggest that the combination of biological properties of several bacterial species within this spring water might be responsible for its regenerative effects on human skin.

La Roche-Posay TSW hydrobiome was also extensively investigated, finding that the predominant strain is Vitreoscilla filiformis, a filamentous bacterium belonging to the Beggiatoales order. Lysates and extracts of V. filiformis have been shown to be effective in the treatment of AD and sensitive skin, and also to strengthen the skin barrier or protecting against UV radiation, exerting anti-inflammatory activities [70,71,72,73,74,89,90]. Although V. filiformis lysates were originally patented by the L’Oréal company, they are currently used in a wide variety of cosmetics and brands.

The hydrobiome of Uriage TSW was also investigated, and the structure of the polysaccharides of Nostoc commune was identified [91], which are of interest in the formulation of cosmetics since they can be used as gelling agents of natural origin. Despite Uriage having patented the so-called “Microbiome Patented Technology based on microbiome”, to the best of knowledge, there are no cosmetics prepared with lysates, fermented extracts or any other compound from the Nostoc commune and Uriage TSW in the market.

Other studies demonstrated that a dermocosmetic formulation containing extracts of V. filiformis, Vichy TSW, niacinamide, hyaluronic acid, and vitamin E was able to repair the skin barrier and regenerate the skin exposed to sudden thermal changes, after skin irritation by tape stripping, and in sleep-deprived women [77]. Furthermore, a recent clinical study showed that an emollient formulation containing V. filiformis can be effectively used as a monotherapy in children suffering from AD and other dermatological diseases, which lead to dry skin [75]. Additionally, a topical formulation which includes Vichy TSW, hyaluronic acid, niacinamide, tocopherol, and probiotic fractions (specific strains not mentioned) helped to prevent skin barrier damage, as well as oxidative stress and inflammation induced by exposome factors such as UV and O₃ [92].

More recently, oil extracts of Phaeodactylum tricornutum from Solia TSW were investigated, showing efficacy in the treatment of sensitive skin when combined with this thermal spring water [76,93]. In this latest clinical study, a cleanser, a serum and a cream were evaluated, finding that skin moisturization, skin barrier function, erythema, elasticity and firmness, and wrinkle depth were significantly improved after a skin care regimen of 28 days.

In the aforementioned publication from Mourelle et al., the cosmetic patents related to TSW hydrobiome were also reviewed, finding that most of them were related to Vitreoscilla filiformis, and some more like Aquaphilus dolomiae [12]. Another patent with the aim of treatment AD described the use of Stenotrophomonas maltophilia bacteria, which are normally present in La Roche-Posay TSW (see Section 5); this strain has been investigated for its role in the restoration of the skin microbiome in patients suffering from AD [94].

The use of derivatives from the hydrobiome of mineral-medicinal and thermal waters presents a promising future for the development of both cosmetics and cosmeceuticals aimed at improving certain skin conditions (acne, rosacea, xerosis, etc.). However, further studies are needed to identify specific communities and strains within each type of thermal water (chloride, sulfate, sulfur, etc.), whether hyperthermal, mesothermal, hypersaline, low-mineralization, etc. Therefore, it is essential to strengthen collaboration among companies, researchers, hydrologists, genetic identification specialists, OMICs experts, and others. In line with this research, the HIDROGENOMA (https://hidrogenoma.dgeg.gov.pt (accessed on 4 March 2026)) and AQUAPRED (https://interreg-sudoe.eu/proyecto-interreg/aquapred/ (accessed on 4 March 2026)) projects, which investigate the hydrobiome of mineral-medicinal and thermal waters, are worth mentioning.

5. Dermocosmetic and Cosmeceutical Patents Based on TSW

Given this increasing scientific and commercial interest, several dermocosmetic and cosmeceutical patents have been filed. In this section, examples of patents related to cosmeceutical formulations from TSW and derivatives for dermocosmetic use are summarized, organized by TSW type and/or trademark (

Table 4. Examples of patents related to cosmeceutical formulations from thermal spring water and derivatives for dermocosmetic use.

Trademark	TSW	Type of Cosmetic/Aim	Patent Number
Pierre-Fabré Dermocosmetique SA (Cauquillous, 81500 Lavaur, France)	Avène	Solution for all galenic forms Preventing and/or treating an inflammatory response of the skin	US10052297B2
	Cauterets or Avène	Liposome gel Treatment of sensitive skin	JP3230239B2
	Avène	Heterogeneous galenic compositions (lotion, make-up removal, sunscreen)	DE69614110T2
Blue Lagoon LTD (Nordurljosavegur 9, 240 Grindavík, Iceland)	Blue Lagoon	Cosmetic formulation Enhancing the skin barrier and anti-aging treatment	EP2026880B1
Azienda Consorziale Terme Di Comano (Località Terme di Comano, 38070 Stenico, Trentino, Italy)	Comano + Mesorhizobium sp extracts	Cosmetic formulation Acne, sensitive skin, dermatological symptoms of psoriasis and AD	IT202000013933A1
Pharmachem Poessneck and Co Kg GmbH (Naßäckerstr. 37-39, 07381 Pößneck, Germany)	Dermbach hot spring	Lotion/cream/Ointment Skin care	DE202022001251U1
Johnson and Johnson Consumer Companies LLC (199 Grandview Road, Skillman, NJ 08558, USA)	Evian	Lotion Promotion of metabolism in skin cells	DE60003541T2
		Cream Skin hydration and metabolism enhancement	DE60000616T3
		Cream Antiaging	EP1170002A1
Nox Bellcow Cosmetics Co., Ltd. (No. 50 Dongfu North Road, Nantou Town, Zhongshan, China)	Jizhou Island Volcanic TSW	Moisturizing formula Moisturizing and skin regeneration	CN105616336A
Léa Nature (23 Avenue Paul Langevin, 17180 Périgny, France)	Jonzac	Delivery system	FR2968553B1
		Cream Improvement of skin microrelief	FR3056106B1
		Cream Healing and repair of skin damage Combating skin aging and skin imperfections	WO2021233988A1
	Rochefort	Cosmetic herbal infusion Anti-aging	FR3098119B1
L’Oréal S.A. (14, Rue Royale, 75008 París, France)	La Roche-Posay + Vitreoscilla filiformis extract	Contour eye cream, gel, stick Eye contour treatment	BRPI0802519A2
	La Roche-Posay + inactivated Stenotrophomonas maltophilia	Dermatological composition Atopic dermatitis	US20160235791A1
Jialan Group Co Ltd. (No.8 Wenhua Road, Economic Development Zone, Choujiang Street, Yiwu 32200, China)	Layuacun	Cream Treatment of sensitive skin	CN112190506A
Laboratoires Dermatologiques d’Uriage (40-52 Bd du Parc, 92200 Neuilly-sur-Seine, France)	Uriage	Prevent skin aging	FR2903303B1
		Treatment of pruriginous or inflamed skin or mucous membranes	FR3015291B1
		Treatment of acne-prone skin	FR2997626B1
		Restore the skin barrier function	FR3039404B1
		Cream Wound healing and skin repair	FR3047897B1
		Cream Anti-aging	FR3092755B1
L’Oréal S.A. (14, Rue Royale, 75008 París, France)	Vichy	All cosmetic compositions Treatment of sensitive skin	US6106846A
		Moisturizing cream Treatment of acne, wrinkles and/or fine lines on the skin	US5997885A
	Vichy + Vitreoscilla filiformis extract	Cream Skin and hair protection	WO2022096649A1
NCPC New Drug Research and Development Co., Ltd. (No. 388 Heping East Rd, Chang’an Dist, Shijiazhuang 050015, China)	Wentang TSW	Moisturizing, preventing inflammation, relieving wrinkles, and whitening	CN101467950A

).

We also found a considerable number of patents for cosmetics prepared with thermal water registered in China, but in most cases, the name of the TSW is not mentioned.

6. Conclusions

Thermal spring waters are no longer simple vehicles but scientifically supported active ingredients with clinically relevant benefits in inflammatory dermatoses, sensitive skin, barrier impairment and photo-induced damage. Their mineral profile, together with bioactive metabolites from their hydrobiome, underpin anti-inflammatory, antioxidant, immunomodulatory, microbiome-balancing and barrier-repair activities, which justify their integration into modern dermocosmetics and cosmeceuticals. The emergence of postbiotic and paraprobiotic fractions from TSW microorganisms has opened a new avenue for microbiome-targeted topical strategies that bridge balneotherapy, dermatology and cosmetic science.

Another conclusion that can be drawn from this review is that independent comparative studies are needed, since the reported studies are mainly supported and self-referenced by companies/commercial brands, although in many cases, they are supported by research bodies.

Regarding the safety, besides the chemical characterization and microbiological quality control, other toxicological studies should be performed, such as heavy metals, organochlorine pesticides or radionucleotides, and for that the application of cheminformatics and bioinformatics tools can facilitate this investigation [95].

Regulatory bodies and scientific societies should work towards a specific framework for cosmeceuticals, including TSW and hydrobiome-derived ingredients, defining acceptable claim categories, minimal evidence thresholds and efficacy and safety requirements.