What is it?
A synthetic form of silica (silicon dioxide) that contains bound water, also known as precipitated silica or silica gel. It is amorphous, meaning its atoms are not arranged in a crystal. In toothpaste it acts as an abrasive that helps clean teeth and as a thickener. In makeup and skin care it acts as an absorbent, keeps powders from caking, adds bulk and makes products more opaque.
Key information
- The CIR Expert Panel concluded in 2019 that synthetically made hydrated silica is safe as used when formulated to be non-irritating.
- It is amorphous (non-crystalline) silica; the cancer risk linked to silica comes from breathing crystalline silica dust at work.
- The same kind of synthetic silica is used in food as the additive E 551, which EFSA found in 2024 raises no safety concern at reported uses.
- In the EU, the safety of nano-sized forms of hydrated silica in cosmetics is being reassessed by the Scientific Committee on Consumer Safety.
More information
Hydrated silica is manufactured rather than mined; the Cosmetic Ingredient Review (CIR) lists precipitated silica, silica gel and colloidal silica among its other names. Its tiny particles cluster into larger aggregates, which the CIR says reduces how much could be breathed in once they are in a product.
The CIR Expert Panel assessed synthetic amorphous silica and hydrated silica in 2019. In the industry survey it cited, hydrated silica was used at up to 33.8 percent in oral care products and up to 10 percent in leave-on skin care. Human patch tests at up to 45 percent showed no allergic reactions, and the Panel found no incidental inhalation risk from cosmetic use. Because silica can dry and irritate skin and eyes, it concluded these ingredients are safe as used when formulated to be non-irritating. It stressed that the conclusion covers only synthetic amorphous forms, not crystalline or mined silica.
Crystalline silica, such as quartz dust from cutting stone and concrete, is a different material: breathing it at work is linked to lung cancer. In food, the European Food Safety Authority concluded in 2024 that synthetic silica used as the additive E 551 raises no safety concern at reported uses, while noting uncertainty about nano-sized aggregates. In the EU, nano forms of hydrated silica in cosmetics are now being reassessed by the Scientific Committee on Consumer Safety, after earlier data were judged insufficient to reach a conclusion.
Reality check: hydrated silica in toothpaste or makeup is not the crystalline silica dust linked to lung disease in workers, and the major safety reviews consider it low risk as used. The open question is limited to nano-sized particles, which EU scientists are still evaluating.
Sources: Cosmetic Ingredient Review: Amended safety assessment of synthetically-manufactured amorphous silica and hydrated silica as used in cosmetics, final report (2019); EFSA Journal (2024): Re-evaluation of silicon dioxide (E 551) as a food additive; European Commission: Request for an SCCS opinion on the safety of hydrated silica (nano) and related silicas (2025); National Cancer Institute: Crystalline silica
