Does clay pull impurities out of pores?

No. It absorbs oil and water from the surface of the skin. Nothing about a mineral sitting on the stratum corneum lets it reach inside a follicle, and the toxin language has no basis at all.

How is bentonite different from kaolin?

Bentonite swells in water and absorbs more aggressively; kaolin is the milder, less absorbent clay. For dry or sensitive skin that difference is the whole decision.

Should I let the mask dry completely?

No. Once it is dry it goes on taking water from the skin, which is where the tightness, flaking and post-mask redness come from. Rinse while it is still slightly tacky.

Can I use a clay mask every day?

Rarely a good idea. The matte effect is short-lived and daily use mostly buys a compromised barrier, which tends to leave skin oilier-looking rather than less.

It absorbs surface oil, which changes how skin looks for a few hours rather than what drives breakouts. Persistent acne is better addressed with ingredients studied for it, and with a clinician if it is scarring.

Bentonite — Ingredient Guide

How it works

Bentonite is a swelling clay, largely montmorillonite, formed from weathered volcanic ash. Its particles are microscopic plates carrying a negative surface charge, and in water they take up many times their own volume and form a gel that is thick at rest and flows when it is stirred. Formulators use that behaviour to hold powders in suspension and to give creams body.

In a mask, the useful property is absorption. As the layer dries it takes up water, surface oil and loose material from the skin. That is a surface process, and the distinction matters: absorbing what is on the skin is not the same as extracting anything from within it.

The evidence

What clay reliably delivers is unglamorous — less shine for a while after a mask, and useful rheology inside a formula. The claims that sell it are a different matter. Drawing out toxins, pulling impurities from pores, deep cleansing: none of this has support, and there is no mechanism by which a mineral sitting on the stratum corneum reaches into a follicle or acts on anything systemic.

The strongest evidence involving bentonite on skin points somewhere else entirely. A quaternium-modified bentonite is used as a barrier preparation, applied before contact with poison-ivy resin, where it physically blocks the allergen from reaching skin. That is a protective role rather than a cleansing one, and it is a better illustration of what clay actually does than any mask claim.

Suitability

Oily and combination skin, occasionally rather than routinely
Not for dry, sensitive or barrier-impaired skin, which will feel it as tightness
Never on broken or inflamed skin
Rinse while the mask is still tacky — drying it to cracking is the point at which it starts taking water the skin needed

Concentration

No meaningful figure exists. In a mask the clay is the base and may run to tens of percent; as a thickener it may be a fraction of one. Neither number predicts how the product behaves, because particle grade, what else is in the formula and how long it is left on matter more than the percentage. There is no established effective concentration for bentonite and any quoted one should be read as marketing.

Conflicts & combinations

No chemical conflict with common actives, but timing does the damage: a clay mask on the same evening as an acid or a retinoid is a routine way to end up with irritation that neither would have caused alone. In principle a charged clay surface can also bind charged actives, so layering a serum directly under a mask is a poor use of both — apply actives after rinsing, on skin that has been given a moisturiser first if it feels tight.