What it is
Hydrated silica is a purified, porous form of silicon dioxide (SiO2) engineered for cosmetic and oral-care use.
In toothpaste it is graded by particle size and hardness to hit a specific RDA (Relative Dentin Abrasivity) target.
Why it matters
Enamel is hard; dentin is not. Abrasive RDA above 250 is considered aggressive; most well-formulated toothpastes sit at 30–100.
Well-graded hydrated silica polishes and removes plaque without meaningfully wearing enamel at typical brushing forces.
Whitening formulations sometimes push silica hardness or add stronger abrasives, which is where the trade-off between stain removal and enamel wear becomes real.
Common uses
- Primary abrasive in most modern toothpaste
- Anti-caking agent in supplements and food
- Cosmetic ingredient for texture and oil control
Safety considerations
- Non-toxic and non-reactive at oral-care use levels.
- Concerns about crystalline silica dust (inhalation hazard in industrial settings) do not apply to hydrated silica in toothpaste.
- Check RDA where published — <100 is gentle, 100–200 moderate, 200–250 aggressive, >250 avoid.
Where you'll encounter this
- Bathroom — toothpaste (nearly universal)
- Kitchen — anti-caking in salt, supplements
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Frequently asked questions
What is a safe RDA for toothpaste?
The ADA considers anything below 250 safe for daily use. Most well-formulated toothpastes sit at 30–100 — plenty of cleaning without meaningful enamel wear.
Is hydrated silica the same as crystalline silica?
No. Hydrated silica is an amorphous, cosmetic-grade form. The industrial inhalation-hazard concerns around crystalline silica dust do not apply here.
Why do some pastes use calcium carbonate instead?
Calcium carbonate is a slightly harder mineral abrasive, often preferred by brands wanting a more traditional feel. Well-formulated calcium carbonate pastes stay within safe RDA ranges too.
Editorial references
- ADA — Abrasivity of toothpaste (RDA guidance)
- Cosmetic Ingredient Review — Hydrated silica assessment
Last updated 2026-07-20.