Bentonite

What it is

Bentonite is a clay formed from weathered volcanic ash, made up chiefly of the mineral montmorillonite. Its platelets carry a negative surface charge and swell in water, so it both soaks up oil and turns a watery mix into a spreadable paste. Formulators use it in wash-off masks for oil absorption and slip, and in emulsions as a stabiliser. Sodium bentonite swells more strongly than calcium bentonite, which is why some masks feel noticeably tighter than others.

What it does well

• Absorbs oil and gives a strong mattifying effect

  The swelling structure and charged surfaces make bentonite one of the more absorbent cosmetic clays, which is why it is the workhorse of 'deep cleansing' masks. The effect is on surface sebum and is temporary.

  Moderate evidence

• Thickens and stabilises mask formulas without synthetic gums

  Bentonite forms a reversible gel network in water, giving the paste its body and stopping heavier powders from settling out. This is a well-established, purely physical formulation function.

  Strong evidence

• Shows anti-inflammatory and barrier-supporting potential in early research

  A 2024 dermatology review found bentonites and montmorillonites can reduce inflammation, aid wound healing and improve hydration and elasticity, but the authors stressed that most evidence is preclinical and that larger randomised trials are still needed.

  Limited evidence

Worth knowing

• Tightening and dryness as the mask dries down

  Bentonite shrinks as it dries and can leave skin taut, red and dehydrated, especially in strong 'pull' formulas. Rinsing before the mask fully cracks, and limiting use to once or twice a week, largely avoids this.

  Matters most toPeople with dry, sensitive, rosacea-prone or already compromised skin.

• Naturally contains trace heavy metals

  Mined clays inevitably carry traces of lead, arsenic and cadmium from the parent rock. EU law addresses this through Article 17 of Regulation (EC) No 1223/2009, which permits the non-intended presence of a prohibited substance only where it is technically unavoidable in good manufacturing practice and the product is still safe. Measurements on topical clay gels found only micrograms per 100 g of arsenic and cadmium were actually released, and the products were judged safe to apply.

  Matters most toNobody at normal wash-off use; the real risk sits with clay that is swallowed, which some 'detox' marketing encourages.

• Inhaling the loose powder is not advisable

  The 2026 Cosmetic Ingredient Review assessment judged bentonite safe as used but said data were insufficient for products that may be incidentally inhaled. Mixing DIY masks in a way that avoids raising dust is sensible.

  Matters most toAnyone handling loose clay powder, particularly around children.

Where the EU stands

Sources (3)

Every link goes to the original: a journal, a PubMed record or an EU document.

1. [1]
   The potential cutaneous benefits of bentonites and montmorillonites

   Archives of Dermatological Research · 2024 · doi:10.1007/s00403-024-03456-5

   A review found bentonite and montmorillonite can reduce inflammation, absorb excess oil and support hydration, but concluded that larger randomised trials are needed to establish efficacy and safety.

2. [2]
   Amended Safety Assessment of Naturally-Sourced Clays as Used in Cosmetics

   International Journal of Toxicology (Cosmetic Ingredient Review Expert Panel) · 2026 · doi:10.1177/10915818261455355

   Bentonite was judged safe in cosmetics at present practices of use and concentration, with the sole reservation that data are insufficient for products that may be incidentally inhaled.

3. [3]
   Healing and edible clays: a review of basic concepts, benefits and risks

   Environmental Geochemistry and Health · 2018 · doi:10.1007/s10653-016-9903-4

   Clays can adsorb toxins but can also carry heavy metals that become available through ingestion or, to a much lesser degree, skin contact - which is why source and purity control matter.