Silica: dangers in cosmetics?

An essential distinction: amorphous silica vs crystalline silica.

Silicon dioxide, also known as silica (silica), is a mineral-based ingredient commonly used in cosmetic products. It primarily functions as an absorbent, mattifying, texturising agent or exfoliant. Although its use is widespread in skincare and make-up products, questions remain about its safety, particularly with regard to its physicochemical form, particle size and route of exposure.

Silicon dioxide exists in two main forms: amorphous and crystalline. The amorphous silica, used in cosmetics, can be either natural or synthetic. It is characterised by low water solubility, chemical inertness and the absence of an ordered crystalline structure. Toxicological evaluations, notably those by the Cosmetic Ingredient Review (CIR) and the Scientific Committee on Consumer Safety (SCCS), conclude that it is safe for topical use, provided it is employed under normal conditions of use.

By contrast, crystalline silica, classified as a Group 1 carcinogen by the International Agency for Research on Cancer (IARC), is toxic by chronic inhalation, particularly in occupational settings.

This form is neither used nor authorised in cosmetic products owing to this proven risk.

Silica nanoparticles: a danger in cosmetics?

The introduction of silica nanoparticles in certain cosmetic formulations (particles <100 nm) has prompted increased scrutiny from regulatory authorities. The SCCS recommends a case-by-case assessment focusing on structure, surface, solubility and bioavailability. Available data suggest that cutaneous penetration of nanoscale silica is very low to non-existent on intact skin. However, if the skin barrier is compromised, permeability could theoretically increase. European regulations require that silica nanoparticles be surface-modified, insoluble and not present in products intended for inhalation, such as sprays or aerosols. To date, no systemic toxic effect has been demonstrated in vivo under normal cosmetic use conditions.

Inhalation of fine particulate matter: the primary identified risk for silica.

The primary risk associated with cosmetic silica concerns the inhalation of particles, particularly in loose powders (foundation bases, finishing powders) or spray products. Even in its amorphous form, silica in suspension can cause irritation of the upper respiratory tract with prolonged or repeated exposure. This risk is increased if particle size is below 10 µm, allowing them to reach the pulmonary alveoli.

The inhalation of fine particles of silica, present in certain cosmetic products in the form of amorphous or crystalline, can cause pulmonary inflammatory reactions and health risks. Studies show that the toxicity of silica depends on the surface structure of the particles. Among these surface elements, the 'quasi-free' silanol groups play an important role. These small chemical groups (≡Si–OH) are sufficiently accessible to strongly interact with human cell membranes, such as those of the lungs. These interactions can damage cells and trigger an inflammatory immune response. If this inflammation persists due to repeated or prolonged exposures (for example, in workers exposed to crystalline silica dust), it can lead to chronic diseases such as silicosis as well as autoimmune disorders.

Silica: skin tolerance and dermatological profile.

The skin tolerance of amorphous silica is generally good. In vitro and in vivo studies confirm the absence of irritation, sensitisation or skin toxicity. Its mechanism of action relies solely on physical properties, such as the absorption of sebum, modification of formulation texture and optical light scattering. Sensations of dryness or transient discomfort may, however, occur on dry or sensitive skin due to its absorbent capacity. When used in a granular (non-spherical) form, silica can also function as a mechanical exfoliating agent. In this case, the choice of particle size is critical to avoid excessive abrasion.

Environmental impact: silica, a sustainable alternative.

From an environmental perspective, silica has a favourable profile. Unlike the microplastics once used as exfoliants (polyethylene, nylon), silica is mineral, non-persistent in aquatic environments, and non-bioaccumulative. It thus offers a sustainable alternative in rinse-off products and eco-responsible formulations.

From an environmental perspective, silica is a more environmentally friendly option. Unlike microplastics such as polyethylene or nylon, formerly used in scrubs, silica is of mineral origin, meaning that it is primarily sourced from sand or quartz. It does not remain in water for long, does not cause lasting pollution in rivers or oceans, and does not accumulate in living organisms. That is why it is considered a more eco-friendly alternative, particularly in rinse-off products or in treatments designed to minimise their environmental impact.