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Bentonite
A swelling clay used in clay masks and some matte styling products as an absorbent and thickener; "bentonite washes" are untested for hair.
What it is
Bentonite is a naturally mined clay, mostly montmorillonite, that swells in water. Its listed cosmetic roles are absorbent, viscosity-increasing agent and opacifier (Elmore 2003). In styling it appears in clay pomades and pastes. See styling products explained. It is not the same as quaternium-18 bentonite, a chemically modified thickener that is reviewed separately.
How it works
It adsorbs oils and some ions onto its layered surface and swells into a gel. Whether that removes product buildup from hair better than shampoo does has not been tested in anything we found.
What the studies show
- A safety review of silicate clays found bentonite not toxic when swallowed in short animal tests. Bentonite injected into a rabbit's eye caused severe inflammation, which is not a use route. Inhalation toxicity depends on particle size and composition (Elmore 2003).
- A 2026 amended review covers 8 naturally sourced clays, and flags insufficient data for incidentally inhaled products for 7 of them. We could not confirm from the abstract whether bentonite is among those 7 (Burnett 2026).
- No hair or scalp outcome study exists. "Clay wash" claims are anecdote.
How it's used in studies
Not applicable.
Side effects and safety
Skin irritation is low. Avoid breathing the powder and keep it out of your eyes. Natural clays can carry trace contaminants, so the source matters. That is a general cosmetic-science caution, not something we found measured for hair products.
Bottom line
Fine as a cosmetic absorbent, with no evidence that it improves hair health. If it suits your scalp, use it occasionally as an oil or buildup mask and rinse very thoroughly. Our confidence is low.
Studies 2
Elmore AR; CIR Expert Panel. Final report on the safety assessment of aluminum silicate, calcium silicate, magnesium aluminum silicate, bentonite, kaolin and related clays. Int J Toxicol. 2003
Result: Not significantly toxic orally in short-term animal tests; inhalation toxicity is readily shown in animals and depends on particle size, concentration and composition.
Read the study ↗Burnett CL et al. Amended Safety Assessment of Naturally-Sourced Clays as Used in Cosmetics. Int J Toxicol. 2026
Tested: 8 naturally sourced clays
Result: Kaolin judged safe as used; the other clays safe except that data were insufficient for products that may be incidentally inhaled.
Read the study ↗Related
- KaolinA soft white clay used in matte clays, pastes and dry shampoos to soak up oil and give a dry, textured finish.
- Silica silylateWater-repelling fumed silica used in texturising powders, sprays and pastes for grip, a dry feel and oil absorption.
- Styling products explainedStyling products come down to how much hold and how much shine you want; there are almost no head-to-head trials, so this page combines formulation knowledge with the few things that have been measured.