Kaolin and bentonite clay

What it is

Kaolin and bentonite are the clays most often used in face masks. Kaolin is a soft white clay that absorbs surface oil and binds fats, proteins and bacteria³. Bentonite is a rock formed from weathered volcanic ash, rich in smectite minerals that swell in water and soak up oil^{2, 3}.

What the evidence says

Evidence: limited. Clays clearly absorb oil, but no good controlled trial shows that a clay mask reduces acne counts.

A drying mask draws sebum into the clay and leaves skin matte for a few hours, which is not acne treatment. The only sizeable human study, an uncontrolled six-week pilot, had people with mild acne use a clay and jojoba oil mask two or three times a week and reported about half as many spots¹. Without a comparison group, it cannot show what the clay contributed. Reviews of bentonite find only a few small studies in nappy rash and hand dermatitis², and whether a clay "kills bacteria" depends on the specific deposit³.

The clearest concern is contamination: clays come out of the ground and can carry lead and arsenic. In 2016 the US FDA warned people not to use a bentonite clay product sold for skin, hair and internal use after finding elevated lead levels⁴, and a Dutch survey found lead above safe limits in nearly all traditional clays sold for eating, and arsenic in almost half⁵. The risk is greatest when clay is swallowed or used on broken skin or children, but an unregulated product is a poor choice for a mask too.

How people use it

• A mask on oily zones, once or twice a week: mix a teaspoon of clay with water to a thick paste, apply to oily areas, and rinse off after 10 to 15 minutes, before it cracks. Mist it so it never fully dries.
• Add a teaspoon of jojoba oil if your skin feels tight afterwards¹.
• Follow with moisturiser.

Cautions

• Once or twice a week is plenty. Daily masks strip oil, the skin makes more, and dry, irritated skin is more likely to develop dark marks, especially in brown and Black skin; see our oily skin guide.
• Buy cosmetic-grade clay from a supplier that publishes heavy-metal testing; avoid clays sold for drinking or internal cleansing^{4, 5}.
• Never eat clay or give it to children^{4, 5}.
• Skip masks on broken, sunburnt or inflamed skin and on rosacea-prone skin, which flares with drying.
• Clay does not treat moderate or severe acne; if spots are not improving after three months, read our natural acne care guide or see a professional.