Application Possibilities of Sustainable Nanostructured Silica-Based Materials in Cosmetics

Abstract

Nanostructured silica-based materials, including mesoporous silica nanoparticles (SiNPs), show a wide range of applications in various areas, such as food, pharmaceutical, and cosmetic industries. This is mainly due to their unique properties, namely biocompatibility, stability, adjustable pore size, a highly developed specific surface area, and simplicity in surface modification. Currently, special emphasis is placed on obtaining nanostructured silica-based materials using so-called green methods, which not only reduce toxic by-products, but also enable the use of raw materials from plants, agricultural and industrial waste, as well as bacteria or fungi. This trend is particularly evident in the cosmetic industry, which is striving to reduce the adverse environmental and social impacts of cosmetic production. Therefore, this article presents a review of the literature from the last ten years, which describes issues related to the possibilities of replacing synthetic silica-based ingredients in cosmetic products with their more environmentally friendly counterparts. Special emphasis has been placed on the application possibilities of sustainable nanostructured silica-based materials and their potential toxicity in topical formulations. The possibilities of obtaining nanostructured silica-based materials through green synthesis and using natural silica precursors have been briefly presented, as well as the options for modifying the surface of these materials.

1. Introduction

For thousands of years, silica’s presence in the Earth’s lithosphere has been known, especially in the form of quartz and quartz sand [1]. Nowadays, an increasing number of cosmetic, food, or pharmaceutical products that contain silica in their composition appear on the market [2]. This is mainly due to the nontoxicity of silica to living organisms and its biological inertness [3]. There are two basic structures of silica: (i) crystalline and (ii) amorphous (Figure 1) [4]. The cosmetic industry primarily uses amorphous silica (AS), which, unlike the crystalline form classified as Group 1 (carcinogenic to humans), is classified by The International Agency for Research on Cancer (IARC) as Group 3 (not classifiable as to its carcinogenicity to humans). However, it should be noted that even if silica in crystalline form was used in a cosmetic product, it would not pose a significant risk in oral or dermal applications, as the carcinogenic potential of this material, according to IARC, has been demonstrated mainly through the inhalation route [5].

Currently, silica nanoparticles (SiNPs) play a dominant role among nanostructured silica-based materials. SiNPs differ significantly from silica in their crystalline form because they have a much more developed specific surface area due to their smaller particle size and the ability to form spatial porous structures [7]. In terms of active substance delivery, the morphology of individual particles is of critical importance, as the carrier particles must be isolated and fall within a size range of approximately 10 nm to several hundred nanometers. It is essential for ensuring that the active substance, both lipophilic and hydrophilic, will be delivered to the site of action and medical or cosmetic formulations remain stable during storage [8].

The cosmetic industry has shown considerable interest in nanomaterials [9]. It specifically refers to nanostructured silica due to its relatively low production cost and hydrophilic surface, which offers easy functionalization. In particular, SiNPs can be commonly found in leave-on and rinse-off cosmetic formulations for skin, hair, and nails, as they improve the efficacy, texture, and shelf life of products, as well as offer controlled release of active ingredients [10]. Currently, 34% of synthesized nanostructured materials are estimated to be used in the production of personal care products, with silica-based materials ranging up to 7% of all nanomaterials applied in cosmetics [11]. Moreover, increased use of nanostructured silica-based materials is expected in cosmetics, personal care, and healthcare products. As reported by Verified Market Reports, the size of the nanosilica market in 2024 was valued at USD 4.5 billion and is projected to reach USD 9.2 billion by 2033, showing a compound annual growth rate (CAGR) of 8.5% between 2026 and 2033 [12]. A particularly strong development of the market for silica obtained through sustainable synthesis procedures is anticipated. According to the Global Market Insights report, in 2023, the global market for “green” silica was valued at around USD 282.8 million and is expected to reach USD 547.2 million in 2032, recording CAGR that exceeds 7.7% between 2024 and 2032 [13]. This reflects an increasing consumer preference for eco-friendly products and the requirements of environmental regulations and sustainability in manufacturing.

Nevertheless, it remains one of the main challenges in the cosmetic industry to replace silica-based materials obtained through traditional chemical synthesis with their counterparts synthesized using more sustainable methods, using natural silica precursors, such as minerals, rocks or clays, and various agricultural and industrial waste products, e.g., rice hulls, husks, straw, and sugarcane bagasse [3]. This approach is based on the so-called green synthesis, the main advantage of which is the use of biological, renewable, and sustainable resources and the absence of toxic by-products. Green synthesis is generally recognized as a vital strategy to minimize the negative impacts associated with conventional techniques commonly used in laboratories or industry. It represents a significant improvement over traditional methods, as it is not only simple and economically viable, but also relatively reproducible and often yields more stable products [14].

Therefore, the primary objective of this paper is to summarize the literature from the past decade concerning the potential application of nanostructured silica-based materials, obtained through environmentally friendly approaches, in cosmetic formulations. While most existing studies focus on materials synthesized via conventional chemical methods, this review emphasizes the potential of replacing traditionally used silica materials with their nanostructured counterparts produced through so-called green synthesis. This includes methods that involve plant extracts, agricultural, and industrial waste, as well as microbial sources, such as bacteria and fungi. The toxicological concerns associated with the use of nanoscale materials in topical cosmetic applications are also thoroughly addressed. Additionally, the paper provides a short overview of green synthesis techniques for nanostructured silica-based materials and briefly describes the resulting materials. The potential for further surface functionalization of these nanostructured materials for use as carriers of medicinal or skin-care agents has also been concisely covered. To the best of our knowledge, no review papers have been published recently that would specify the latest advances in the possibility of using nanostructured silica-based materials obtained by green synthesis as both auxiliary and functional ingredients in cosmetic formulations. In this context, the review paper on the current possibility of using sustainable silica counterparts may not only advance scientific innovation, but also reinforce a commitment to environmentally responsible industrial practices.

2. Synthesis of Sustainable Nanostructured Silica-Based Materials

At present, nanotechnology is considered one of the most important areas of science. Its potential of multiple applications has paved the way for the introduction of increasingly new and innovative methods for the synthesis of nanostructured materials [15].

Since 1968, when the group of Stöber described the synthesis of silica nanoparticles using tetraethoxysilane (TEOS) as a source of silica, ethanol and water as solvents in the presence of ammonia [16], many papers have appeared on the synthesis of silica nanoparticles. These syntheses were carried out mainly through the use of chemical modification and/or optimization of the aforementioned method [17,18,19,20] with the following examples: “top-down” and “bottom-down” syntheses [21]; sol–gel [22,23]; chemical vapor condensation, [24]; flame synthesis [25], which over the years has led to the various forms of silica particles and nanoparticles (Figure 2).

However, the methods mentioned above have some disadvantages, such as (i) the high cost of the reagents and apparatus used [27,28]; (ii) the toxicity of the reagents, [29]; and (iii) limited control over the size, morphology, and phase composition of particles [30]. In addition, they can consume great amounts of energy and generate large quantities of waste. This led to the search for more environmentally friendly solutions to counteract these problems and led to the development of the so-called green methods in the synthesis of SiNPs (Figure 3). A brief comparison of traditional methods with the so-called green protocols for nanomaterial synthesis is presented in

Table 1. Traditional synthesis methods of silica nanoparticles vs. so-called green synthesis methods.

Traditional Synthesis Methods
Disadvantages	Advantages
The use of large amounts of organic solvents—negative impact on the nervous and reproductive systems of living organisms [32].	Obtaining a wide range of nanoparticles with diverse properties [15].
Use of high pressures and temperatures [33].	Relative simplicity of procedures for nanoparticle synthesis with two main approaches: top-down and bottom-up [21].
Generation of volatile vapors [34].	Control over the morphology of nanoparticles [35].
Excessive carbon dioxide production, contributing to the greenhouse effect [36,37].	The ability to scale up processes [38].
Ecological (Green) Synthesis Methods
Disadvantages	Advantages
The impact of geographical differences on the acquisition of biological research material [39].	The use of microorganisms (bacteria, yeast) and certain species of algae and plants as substrates for synthesis [40].
Low reproducibility of the results [39].	Ensuring that nanomaterials have the proper characteristics, e.g., antibacterial properties [41].

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When using other “green” methods for the synthesis of silica nanoparticles, some of the disadvantages mentioned above can be minimized, as they are compensated for by the advantages of these methods (e.g., lower energy consumption, reduction in the use of harmful and hazardous reagents) [40]. Since more environmentally friendly reagents replace harmful ones, the particles obtained are less toxic than those synthesized by chemical methods, which has been confirmed in review articles by Karande and Khoshnazar [42,43]. For example, silica nanoparticles synthesized from olive ash residue showed significantly lower toxicity to fibroblast cells than commercially available nanoparticles [44]. Ecological (so-called green) methods of synthesizing nanomaterials use natural and biological systems for their production [15]. These include minerals and clays, as well as plants, algae, fungi, and yeast, which are composed of naturally available biomolecules that play a role in the formation of biosilica nanoparticles (Figure 4).

The use of biological, renewable, and sustainable resources enables the development of green, straightforward, and cost-effective strategies for nanoparticle production, thereby reducing or eliminating the need for labor-intensive and complex procedures. The so-called green and eco-friendly syntheses of SiNPs from diverse sources represent environmentally benign, uncomplicated, and frequently one-pot reaction systems.

2.1. Clays/Minerals

Clay minerals are a class of silicates with chemical inertness, colloidity, and thixotropy that exhibit good physicochemical properties, characterized by biocompatibility and low toxicity [46]. Among the clays and minerals used to obtain silica is Malatya Pyrophyllite. This clay mineral has been described, among others, by Yadav et al. for the synthesis of SiNPs [45]. In turn, Zulfiqar and colleagues obtained SiNPs using bentonite clay [47]. It is also possible to obtain biosilica from volcanic pumice rock, as demonstrated by Mourhly et al. and Rahmadianti et al. [48,49].

2.2. Agricultural Waste Products, Plants, and Industrial Waste

The main advantage of using agricultural waste products is their high availability, especially at the end of harvest [45,50,51]. In addition, the use of waste materials helps reduce the cost of silica synthesis. It also minimizes the need for hazardous chemicals and promotes the development of green synthesis protocols [40]. A silica-rich substrate is rice husk, the use of which has been widely documented in the literature for the production of high-quality nanosilica [3,52]. In addition, rice husk to obtain SiNPs has been used, among others, in research by Singh et al. [53], Ijaz et al. [54], Younes’a et al. [55], and more recently, Djafaripetroudy [56] and Zewide et al. [57].

Another example of waste that may serve in silica synthesis is sugarcane. Processing sugarcane to produce sugar and ethanol generates a large amount of waste. The ash from this waste contains large amounts of silica, through which a number of methods have been developed to obtain SiNPs (Figure 5) [58,59,60,61,62] and biogenic amorphous silica in the form of microspheres for sustainable cosmetics [63] as well as for further applications.

Waste from coconut husks [64], sugar beet bagasse [65] or cassava [66,67] was also used.

Synthetic methods for obtaining silica nanoparticles very often use plant extracts as reducing or hydrolyzing agents [42]. SiNPs or biosilica can be obtained from various parts of plants, such as bamboo leaves [68,69] or banana stems [70].

2.3. Algae

According to numerous reports in the literature on nanosilica synthesis, diatoms are most often cited among this group of biosilica precursors [71,72,73,74,75]. These unicellular algae are characterized by the fact that they synthesize and enclose themselves in a highly ordered, three-dimensional, porous cell wall, called a frustule, which is made of amorphous silica [76]. The structure of diatoms depends on their species and can include a variety of forms, such as hexagonal, rod-shaped, and circular [77] (Figure 6).

2.4. Bacteria and Yeast

Currently, bacteria are considered to be among the most efficient systems used in industry, referred as “nanofabrics” [42]. The following bacterial strains, among others, have been used to synthesize silica nanoparticles or nanosilica: Escherichia coli [14], Bacillus subtilis [78], Burkholderia eburnea [79] and Enterobacter ludwigii [80].

Yeasts are among the simple eukaryotic organisms that can be successfully used for the synthesis of silica nanoparticles; for example, yeast Saccharomyces cerevisiae has been used for the biochemical synthesis of SiNPs [81,82].

2.5. Fungi

Fungi from the genera Fusarium, Aspergillus, and Penicillium show a high potential for use in the synthesis of silica nanoparticles [83,84,85]. In addition, silica nanoparticles have also been synthesized from rice husk by fermentation using the Python fungus [42].

Examples of silica nanoparticles synthesized from different natural sources, together with their basic properties, namely size and morphology, are listed in

Table 2. Silica nanoparticles synthesized from different natural sources.

Silica Source	Properties of SiNPS	Ref.
Clays/minerals
Bentonite	69–223 nm	[47]
Kaolinitic clay	21–30 nm; amorphous silica; homogeneous morphology with agglomerated particles.	[86]
Agricultural waste products, plants, and its industrial waste
Rice Husk	400 nm; spherical particles.	[87]
Wheat husk	100–200 nm; spherical particles.	[88]
Pine cone and pine needles	30–60 nm; quasi spherical particles.	[89]
Paddy straw	17 nm; spherical particles.	[90]
Corn cob husks	40–70 nm; spherical particles.	[91]
Algae
Gracilaria crassa	20–50 nm; amorphous; spherical particles.	[92]
Cylindrotheca closterium	7–17 nm; spherical particles.	[93]
Bacteria and yeast
Azospirillum brasilense	100–200 nm; spherical particles.	[94]
Fungi
Pleurotus ostreatus	5–15 nm; spherical particles.	[94]
Lentinula edodes	50–100 nm; spherical particles.
Grifola frondosa	5–15 nm; spherical particles.
Ganoderma lucidum	50–100 nm; spherical particles.
Agaricus bisporus	30–60 nm; mesoporous.
Agaricus arvensis	30–20 nm; spherical particles.
Penicillium oxalicum	20–50 nm; crystalline nature.	[84]

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3. Modification Possibilities for Nanostructured Silica Materials

In order to expand the possibilities of using silica in various areas, its surface must be modified (functionalized). Silica contains silanols (Si–OH functional groups, Figure 7a) on its surface. Silanols attract molecules and react with hydroxyl, carboxyl, and oxide groups. The surface of silica can be hydrophilic or hydrophobic, depending on the presence of silanol. The higher number of silanols increases hydrophilicity, enabling the formation of hydrogen bonds with water. There are three types of silanols: isolated, geminal, and vicinal (Figure 7b). Only adjacent silanols, located less than 3 nm apart, can form hydrogen bonds and interact strongly with water. Crystalline silica is more hydrophobic, whereas mesoporous, colloidal, and precipitated silica are hydrophilic. The surface of SiNPs can be modified, for example, by depositing PFOS (perfluorooctyl trichlorosilane), which increases hydrophobicity [45].

So far, numerous attempts have been made to functionalize silica surfaces, as the silanol groups present on the surface of silica matrices enable the incorporation of various organic and inorganic groups, metal atoms, or groups containing heteroatoms. In addition, silanol groups present on the surface of silica or SiNPs, without prior surface functionalization, could interact with biological molecules, modifying the structure of these forms. Appropriate functionalization of the porous surface of silica/silica nanoparticles using, for example, functional groups makes it possible to modify their walls, pore entry, and external and/or internal surface (Figure 8).

These modifications can occur through, among others, the following: (i) lipid coating, where the presence of an outer lipid layer around the silica nanoparticles improves the interaction with the skin layers, enhances the biocompatibility, and minimizes the aggregation of the obtained nanoparticles [95,96]; (ii) introduction of positively charged functional groups (e.g., NH₂), that improves the skin permeation of SiNPs, as the first stage of skin permeation involves attachment of nanoparticles to the cell membrane of skin cells. Epithelial cell membranes on the skin surface have a negative charge, thus the modification of SiNPs with positively charged functional groups supports these interactions [97]; (iii) use of targeting agents, e.g., modification of SiNPs with polyethylene glycols (PEGs) affects their permeation at a specific site in the skin, for example, through skin appendages [98]. The use of PEGs allows the formation of a hydrophilic layer around the functionalized materials, which also enhances the dispersion of SiNPs [2].

4. Characteristics of Nanostructured Silica Materials

The structure of nanoparticles is generally determined by the chemical composition of the material, the number of atoms in the particle, and the nature of chemical interactions between atoms. Nanoparticles can be crystalline, amorphous, or form pseudo-close packing structures, not described by any of the crystallographic space groups [3,99]. The physicochemical parameters of the particles or nanoparticles play a key role in transporting active substances to a specific site in the body and include (i) size, (ii) shape, and (iii) porosity [26].

The loading capacity of porous silica nanoparticles can be optimized if the porosity is high. Additionally, with appropriate synthetic protocols, the particle size can be fine-tuned to navigate through specific biological barriers. Biodegradability can be adjusted over a rather broad range, enabling control of release rates, even though the degradation of the carrier is not the sole mechanism of release. Compared to larger particles, nanoparticles are more readily degraded, allowing for faster removal from the body. The final product of the degradation of the silica component in the drug carrier is silicic acid, which is physiologically benign and for over 50 years has been considered safe by the FDA [8].

The most common morphological structures of silica nanoparticles are non-porous silica nanoparticles, mesoporous silica nanoparticles, hollow mesoporous silica nanoparticles, and core–shell silica nanoparticles (Figure 9).

Mesoporous silica nanoparticles are composed of colloidal amorphous SiO₂ and synthesized primarily using sol–gel methods. The use of surfactants as structure-directing agents, operating under dilute conditions, facilitates the production of monodisperse spherical particles with well-defined mesoporous structures. Mesoporous SiNPs exhibit tunable physicochemical properties, including particle size, pore volume, pore size distribution, surface area, and surface functionality. Their porous architecture provides internal cavities capable of encapsulating and releasing diverse biomolecules and therapeutic ingredients. This versatility in size, morphology, and textural parameters has established mesoporous SiNPs as promising nanocarriers in the controlled drug delivery. Specifically, mesoporous SiNPs synthesis protocols allow precise control over particle diameter and porosity geometry, enabling the creation of materials with parallel channels or radial arrangement of pores [101].

The size of the obtained nanoparticles, which may range from 10 nm to 500 nm, regulates their cellular absorption and biocompatibility. This parameter is usually controlled by changing the reaction parameters. Furthermore, many studies have shown that shape, in addition to size, plays a decisive role in modulating the physiological behavior and activity of nanoparticles [100].

The most common shapes of silica nanoparticles are nanospheres and nanorods (Figure 10), which have been synthesized for a wide range of therapeutic and diagnostic applications.

5. Sustainable Nanostructured Silica Materials in Cosmetic Products

Nanostructured silica-based materials synthesized using so-called green methods exhibit a variety of possible applications, particularly in areas such as cosmetics and drug/active substance delivery. The use of silica materials in cosmetic products allows them to achieve increased stability and long-lasting application effects. Furthermore, the large specific surface area of silica nanomaterials allows more efficient absorption and transport of active ingredients through the skin [10]. Thus, two main applications of silica materials in cosmetics are becoming apparent, i.e., as an auxiliary substance supporting the stability of formulations and as a platform supporting the delivery of skin care ingredients.

5.1. Potential Toxicity of Topical Formulations Containing Nanostructured Silica

Cosmetic products concentrate their action within the skin. Thus, from the point of view of safety and the development of further possible applications, it is of utmost importance to understand the issues related to the interaction and skin penetration of silica materials, especially those in the form of nanoparticles [102]. To this end, many studies have been conducted that seek to understand which parameters, including size, shape, and surface properties, have the greatest impact on the penetration of silica nanomaterials into the deeper layers of the epidermis. Although stratum corneum penetration is challenging for products applied to the skin, the possibility of nanoparticles reaching deeper layers of the skin must be taken into account due to a number of possibilities for penetration into adjacent layers through the intercellular pathway (between cells), the transcellular pathway (crossing cell membranes), or through cutaneous appendages [103].

Amorphous silica is acknowledged as “Generally Recognized As Safe” (GRAS) by the FDA and EFSA and has been widely used in food, drugs and cosmetics [104]. It is also worth noting that synthetic amorphous silica (SAS), which is the main form of silica currently used in cosmetic products, is a nanostructured material in which individual particles aggregate with each other to form systems exceeding 100 nm, often reaching micrometer and even millimeter sizes. The release of individual nanoparticles from such agglomerates is a thermodynamically very unfavorable process and requires large amounts of energy. Therefore, it can be concluded that toxicological risks would not be relevant for cosmetics applied dermally or orally [105].

Recent studies have shown that SAS, when incorporated into the formulation of standard cosmetic products, does not exhibit the ability to penetrate the skin of pigs and humans into the systemic circulation, and therefore does not pose a toxicological risk [106]. Studies on the toxicity of bio-based amorphous silica currently focus primarily on the environmental impact of the obtaining process [107], usually bypassing issues related to the toxicity of such materials on living organisms and relying on reports on traditionally obtained SAS. However, recently, Costa et al. presented the results of their study on the toxicity of biogenic silica microparticles with potential application in cosmetic products, indicating the absence of their toxicity against skin keratinocytes [108].

A similar study was conducted by Alshatwi et al. and involved highly pure amorphous and spherical biogenic silica nanoparticles with 10–30 nm size obtained from rice husk. Biocompatibility with human lung fibroblast cells (hLFCs) was investigated using a viability assay. Cellular morphological changes, intracellular ROS generation, mitochondrial transmembrane potential, and oxidative stress-related gene expression were evaluated, demonstrating that synthesized spherical biogenic silica nanoparticles are biocompatible and thus can be considered an alternative option to synthetic forms of silica in biomedical applications [109].

However, in the case of silica nanoparticles, their effects on the body may differ from those of bulk materials, and thus their profiles of interactions with the human body may be quite dissimilar. Of particular concern with regard to the use of nanosilica in cosmetics is the possibility that it penetrates the skin and is capable of reaching internal organs or the bloodstream, where it can exhibit toxic effects. In the case of dermal exposure, one possible way to assess the risks of nanomaterials used in cosmetics is to determine whether dermal absorption occurs after exposure. A growing number of studies have focused on in vivo testing of the systemic toxicity generated by topically applied SiNPs [110,111].

Many of these reports are limited to presenting particle–cell interactions based on in vitro studies conducted on 3D skin models. They focus primarily on the skin permeation of SiNPs, but also point out further potential interactions and ways to eliminate them from the body. Because the silica nanoparticles used in cosmetics are administered predominantly to the skin, toxicity tests for this route of administration become essential to outline the full picture of any possible effects of exposure of the skin barrier to SiNPs [112]. Although the number of literature reports describing human clinical trials is still small, studies conducted to date with solid silica nanoparticles have shown that they are safe for human use and improve the therapeutic efficacy of the active substances used. Nevertheless, future research should focus mainly on critical aspects of the use of SiNPs, such as the safety of long-term exposure and the establishment of long-term toxicological profiles that would take into account various routes of administration of SiNPs [113].

The Scientific Committee on Consumer Safety (SCCS) opinion, issued on the basis of the latest studies, indicates that no conclusive evidence has been found that nanosilica penetrates the skin or is toxic, while finding insufficient evidence to completely rule out this possibility. More data are needed before it can be considered completely safe or dangerous. In particular, more evidence is needed to ensure that nanosilica does not penetrate the skin, especially in the case of skin damage. In the case of internal exposure, potential genotoxic, carcinogenic, and reproductive effects would also need to be evaluated [114].

In addition, processes used to manufacture and/or modify SiNPs should be considered holistically in assessing their toxicity, as they can significantly affect the physicochemical and morphological properties of SiNPs, leading to substantial differences in the properties of different batches of the same material. They can also introduce various impurities and other residual materials into cosmetic products [115].

Studies in which the toxicity of silica nanoparticles was correlated with their physicochemical properties, not just with dosage, exposure time, and the type of formulation used, should also be addressed [116,117,118,119]. Some researchers have found that the toxicity of SiNPs is affected by their porosity, which manifests itself as increasing toxicity in correlation with increasing pore size. In addition, a larger specific surface area can cause an increased adhesion of SiNPs to biological structures, triggering greater adverse effects [120,121,122]. Accordingly, modifications are being considered at the SiNP synthesis stage, leading to nanosilica with well-defined and tunable parameters, including size, composition, and surface chemistry, which will allow for the tailoring of the toxicity profile of SiNPs, with a particular focus on reducing toxicity and increasing biocompatibility [116,123,124,125].

5.2. Applications of Silica-Based Nanostructured Materials in Sustainable Cosmetics Products

Silica is a component of many cosmetic products. For example, it can be found in leave-in and rinse-off products for the face, lips, skin, hair, and nails, where it enhances the effectiveness, texture, and shelf-life of cosmetic products. It also improves absorbency and serves as an anticaking agent [10].

Recently, bio-based silica microparticles have been proven as an emulsion-stabilizing agent. Costa et al. developed a new cosmetic ingredient based on biosilica microparticles obtained from sugarcane ash by sustainable processing. Accelerated stability tests (at 40 °C and 75% RH) of the final product highlighted, among others, that after 30 weeks, the silica microparticles were able to maintain their spherical shape without any significant agglomeration that resulted in emulsion instability. Moreover, biosilica microparticles exhibited bioactive benefits to the skin with potential anti-aging and regenerative effects. These were confirmed by stimulating procollagen I production and migration of skin fibroblasts to wounded areas, respectively, giving the basis for potential applications in anti-aging or regenerative products. This has also been supported by topical safety studies, which have shown that biosilica microparticles at concentrations of up to 5% (w/v) are not cytotoxic in skin keratinocytes, as well as non-sensitizing to skin peptides [108].

Additionally, the group of Costa synthesized biogenic amorphous silica in the form of precipitated and silica gel microparticles using sugarcane bagasse ashes. The presence of nanometric particles and heavy and potentially sensitizing metals was assessed, proving that they are safe and suitable for cosmetic applications. The oil and water absorption capacities were also determined, and it was found that they are satisfactory in terms of the potential application of the synthesized silica microparticles in cosmetic products as a sweat- and oil-absorbing agent that decreases light reflection and improves soft focus and mattifying effects. Furthermore, a process development study followed by cost analysis led to optimization of the synthesis, ensuring the economic feasibility of the obtained silica [63].

On the other hand, the study by Tafuro et al. aimed to replace synthetic ingredients responsible for the rheology and texture of cosmetic products with their more natural counterparts while maintaining their stability, ease of application, or sensory aspects. To this end, synthetic texturizers, such as nylon−12 and PMMA (polymethylmethacrylate), were replaced with starch, maltodextrin, and silica (with particle size in the range of 2–20 µm). Among other things, the study showed that replacing the synthetic texturizer with silica allowed for reproduction of the rigid structure and the low pick-up value of the original formula. Nevertheless, some small disadvantages were also observed, as the reformulated emulsion was somehow less spreadable and had a thicker consistency than the commercial one. However, the authors state that cosmetic formulations with environmentally friendly raw materials, such as silica of natural origin, can support the global cosmetics industry in the focusing on sustainability and compelling companies to develop innovative eco-friendly products [126].

The AS particles, which are typically composed of primary nanometric particles combined in the form of aggregates of different particle sizes, have been widely used in long-wear color cosmetics, usually as sebum and sweat control agents. In solid lipsticks, surface-treated AS particles can also be used as an oil gelling and structuring agent that supports improved product transfer, particularly in highly pigmented formulations. Additionally, AS particles enhance the storage and temperature stability of wax-based color cosmetics [127].

Silica particles in combination with biosurfactants were also tested in the formulation of a sustainable lip gloss emulsion. Drakontis et al. established that the diameter of the silica particles and their concentration had a substantial influence on the viscosity profile and stability of the formulation. Specifically, particles with larger diameters (approximately 14 nm) were shown to significantly influence the parameters connected to the elasticity of the product, namely the storage and loss moduli. The formulation obtained ensured easy application of lip gloss and its fixation to the lips due to the presence of silica particles [128]. It has also been shown that silica nanoparticles may not only help expand the appearance and distribution of pigments in lipsticks, but also prevent pigments from migrating into the fine line of the lips [129].

Porous hollow silica microspheres with a narrow size distribution were applied in a new method for obtaining hydrophilic liquid oil formulations. The encapsulation and solidification of Jojoba oil can provide a useful solution for unstable active compounds used in topical applications, such as vitamins A, D, and E, providing both the compound protection and hydrophilic formulation. According to Belostozky et al., the oil-filled silica microspheres dispersed in a hydrogel created a homogeneous water-based formulation that appeared stable, even after six months of storage. Moreover, the materials obtained were found to be non-toxic to a spontaneously transformed human epithelial cell line from adult skin (HaCaT cell line) [130].

Organic hollow mesoporous silica systems were also tested as an environmentally friendly substitute for microplastics used, among others, in cosmetic products. Xiao et al. synthesized such a novel mesoporous silica system with a high loading capacity and outstanding adsorption characteristics by using n-octyltrimethoxysilane (OTMS) and tetraethoxysilane (TEOS) as silicon sources. The silica obtained was tested as a carrier for sandalwood essential oil, enabling its feasible dispersion in water and reducing the shortcoming of volatility, thus expanding its potential application as a cosmetic ingredient. Moreover, it could also be used as a stabilizing agent during the formation of the Pickering emulsion. All these advantages establish organic hollow mesoporous silica systems as a potential microplastic replacement with wide prospects in the cosmetics and personal care industry [131].

The encapsulation process can guarantee the stability of compounds that are sensitive to external factors. Therefore, Costa et al. obtained biogenic silica by extracting sugarcane bagasse ash and tested it as a biocompatible system for the encapsulation of retinoids in order to increase their stability and skin activity. The encapsulation of retinol in silica microparticles provided its photoprotection, as well as thermal and oxidation stability. It also guaranteed the bioavailability and safe use of retinol in cosmetic and dermatologic products by minimizing some potential side effects, such as irritation, dryness, and flakiness of the skin. According to the published results, retinol encapsulation within silica particles allowed an increase in its minimal non-cytotoxic concentration towards HaCaT cells from 0.04 μg/mL to 1.25 mg/mL. It supported the conclusion that a gradual and sustained delivery of retinol could be achieved. Furthermore, encapsulated retinol should allow the acquisition of more stable cosmetic products with a prolonged shelf life [132].

Korkmaz et al. reported that SiNPs obtained with the waste management and sustainability efforts, namely using waste leaves from industrial hemp waste, can have remarkable biological properties. According to the study, they can suppress cell proliferation and affect apoptosis-related genes expression in breast cancer cells, as well as inhibit acetylcholinesterase enzyme activity (AChE) and show an antibacterial effect [133].

The antibacterial and antifungal effect of citronellol-functionalized biogenic silica was also demonstrated by Lopez et al., who modified diatomaceous earth or diatomite with quaternary ammonium salt and a biogenic compound, and showed particularly marked inhibition against A. fumigatus and C. globosum strains. This could be attributed to a synergistic interaction between quaternary ammonium salt and citronellol, as the cationic moieties can induce membrane disruption, thereby facilitating the intracellular penetration of citronellol. It is worth noting that the antifungal activity was sustained over time, what has been proved in tests repeated after 9 days [134].

The interest of the cosmetic industry in silica-based nanostructured materials is significant, and its market share in cosmetic products is expected to grow steadily [135]. This is mainly due to the relatively low production cost of these types of material. Additionally, silica-based nanostructured materials have a hydrophilic surface that promotes numerous chemical modifications, which in turn allows them to be used as carriers for both hydrophilic and hydrophobic substances (Figure 8).

Functionalized mesoporous silica particles with different arrangements of mesopores, namely SBA-15 and SBA-16, were applied as carriers for controlled release of niacinamide, which is an ingredient of great importance in cosmetic products. These types of materials link the features of a relatively stable and chemically inert amorphous silica matrix with well-defined structural/textural parameters and organic functional groups that provide specific chemical properties. The maximum loading with niacinamide (16 wt.%) was observed for the unmodified SBA-15 carrier, while the highest degree of niacinamide release characterized the functionalized SBA-15 sample (60% after 24 h), showing that the type of nanostructure and the presence of functional groups affect the release profile of niacinamide from the mesoporous silica [136].

Silica nanoparticles, especially in their mesoporous form, can be a valuable material supporting the delivery of active substances with skin care and/or therapeutic effects. They can be used for oral and transdermal delivery, as at present, both of these routes have been recognized as safe for amorphous silica [104,114]. Mesoporous silica nanoparticles are characterized by a large specific surface area and a significant pore volume, which allows for a high loading of the active ingredient. This was used in the design of gels saturated with silica-supported azelaic acid for advanced topical skin rejuvenation and depigmentation therapy. This approach allowed more efficient delivery of the active ingredient compared to conventional methods, with an effective entrapment of the active ingredient as high as 93.46%, and highlighted the possibility of applying mesoporous silica to address pigmentation concerns in cosmetics and dermatology. However, the long-term stability and biocompatibility of the obtained formulation remain unknown, highlighting the need for additional research, including prolonged stability tests [137].

An increasing concern regarding the adverse health and environmental effects of cosmetic UV filters encourages many research groups to find safer alternatives. Nanoencapsulation of traditional organic UV filters in silica particles or coating the surface of inorganic materials with silica layers can be considered a promising approach to improve photostability and UV blocking ability, as well as to reduce health risks. Nanoencapsulation improves the retention of organic sunscreens in the upper layers of the skin and adjusts the penetration and release profiles of active molecules according to the novel design of nanoparticles [138].

Hierarchically mesoporous silica particles with high specific surface area and photostability were applied in UV-shielding cosmetic products as a support for avobenzone delivery. Avobenzone is one of the few organic UVA filters commonly used in broad-spectrum sunscreen products, but under UV light, it has a poor stability. The study by Wang et al. proved that encapsulation in silica saved its excellent UVA absorption properties and enhanced stability, thus preventing the formation of harmful photodegradation products from avobenzone [139]. Another example of the use of mesoporous silica as a carrier to support the use of avobenzone in sunscreen cosmetic products is the research by Knežević et al. who obtained mesoporous silica nanoparticles and periodic mesoporous organosilica nanoparticles containing different bridging moieties, all characterized with high stability toward photodegradation. According to their study, the size and composition of silica particles significantly influenced UV protection efficacy, with periodic mesoporous organosilica particles containing UV-absorbing benzene moieties in the framework and with a diameter of ca. 350 nm displaying the highest SPF values [140].

Choi et al. developed a very simple, cost-effective, and scalable synthesis procedure for obtaining a multi-interfacial SiO₂-TiO₂-polyphenol heterojunction, which may serve as a highly efficient and plastic-free cosmetic UV filter with diminished photocatalytic reactivity. Mesoporous SiO₂ was applied as a template for the on-surface synthesis of TiO₂ nanoparticles, followed by tannin deposition. This approach, through the joint effects of the extended absorption spectrum, suppressed ROS generation, and reduced cell and tissue penetration, opens a new pathway to more safe, efficient, and environmental-friendly UV shielding ingredients dedicated to topical applications [141].

Similar conclusions were drawn by Ma et al., who invented a two-step procedure for the encapsulation of cosmetic UV filters into solid SiO₂-sealed mesoporous silica nanoparticles. First, two common filters with a complementary UV shielding range, namely TiO₂ and DHHB (diethylamino hydroxybenzoyl hexyl benzoate), were encapsulated into large mesoporous silica nanoparticles. Then, a SiO₂ coating was applied in order to seal and stabilize nanocapsules. The materials obtained were characterized with good mechanical stability and minimized the release and skin penetration of the sealed DHHB and TiO₂. Moreover, its addition to the cosmetic formulation expressed excellent sunscreen performance with coverage of the entire UV radiation range [142].

Consecutively, Yoo et al. proposed UV filters for simultaneous UVR absorption/reflection, prepared on the basis of biocompatible and biodegradable organosilica nanoparticles with self-encapsulated phenyl moieties. The obtained material was clearly transparent and had low opacity compared to typical inorganic filters. Moreover, during in vitro tests, it was shown that after incubation for 24 h, the viability of NIH 3T3 fibroblast cells exceeded 90% for the entire range of concentrations (0.0–0.5 mg/mL) of organosilica nanoparticles. The ex vivo penetration study performed using a pig skin model revealed that after 4 h of topical application, nanoparticles had a tendency to adhere to the outer layers of the skin without penetrating the dermis [143].

In general, silica nanoparticles in the form of stabilized nanodispersions with a particle size in the range of 5 to 100 nm can also be used as a material for the encapsulation process, which can help transfer of lipophilic and hydrophilic substances through the stratum corneum to their site of action in the epidermis [144].

However, in addition to the above-mentioned possibilities for the use of sustainable silica-based nanostructured materials in cosmetic products, parallel research is also being conducted on the participation of these materials as carriers of active substances in supporting the treatment of certain dermatological conditions [145]. In recent years, there have been several such reports, ranging from antioxidant [146,147], antifungal [148,149,150] and antibacterial activities [151,152,153], to support wound healing [154,155,156], and skin cancer therapy [157,158]. Although these studies show promising results, they are still at an early stage and require further extended testing.

6. Summary and Future Perspectives

The cosmetic industry is eager to take advantage of the new discoveries resulting from scientific studies that confirm the safety and effectiveness of ingredients. However, the modern market of cosmetics is paying attention not only to the development of formulas that will solve specific dermatological problems, but also to the attempt to meet additional consumer demands, particularly those related to environmental friendliness. This trend undoubtedly includes research on sustainable nanostructured silica-based materials, the results of which are promising, especially for the support of skin photoprotection and the encapsulation of active ingredients with low stability and solubility in an aqueous environment. Nevertheless, a greater understanding of the manufacturing process of sustainable nanostructured silica-based materials is still essential, including scaling, reproducibility, cost-effectiveness, and safety issues. This is particularly important in the case of materials obtained by the bioprocessing of natural silica precursors. This approach, on the one hand, allows the use of waste materials, which increases the ecological aspect and introduces elements of sustainability, but on the other hand, it carries the risk of undesirable substances contaminating the obtained silica materials. There is also a lack of systematized knowledge about the possibility of producing sustainable nanostructured silica-based materials on an industrial scale, which would ensure their continued access for cosmetic manufacturers.

Overall, it can be suggested that SiNPs, when compared with non-porous silica nanoparticles, have a particularly great potential in the cosmetic industry due to their unique characteristics, namely adjustable surface area, tunable particle and pore size, high loading capacity, and quite good biocompatibility. However, in addition to many promising results, future studies should focus on critical aspects of SiNPs application, such as safety during continued exposure and long-term toxicological profiles, taking into account different ways of administration, with a special emphasis on the dermal route. Concerns about the potential risk of use and exposure to silica nanoparticles in cosmetic products are still indecisive, and therefore further chronic tests are required. In addition, factors such as size, surface modifications, and purity in silica-based nanostructured materials should also be taken into account during toxicity evaluation. Unfortunately, the lack of standardized toxicological methods and procedures for in vitro, ex vivo, and in vivo skin experiments to adequately compare results between different research groups can become somewhat an inhibitory factor. The lack of randomized, evidence-based clinical trials with a focus on testing SiNPs therapeutic efficacy and safety of SiNPs in topical application is also apparent, forcing the use of current regulatory frameworks established by the FDA/EU Cosmetic Regulations.

Nonetheless, it can be concluded that the innovative and green syntheses of sustainable nanostructured silica-based materials represent a promising future for the cosmetics market, which is increasingly focused on obtaining eco-friendly cosmetic products by minimizing and valorizing waste.