What it is
Quaternium-18 bentonite is bentonite clay that has been surface-treated with the quaternary ammonium compound quaternium-18, making it compatible with oil phases. In sunscreens it is used to thicken the oil phase and to suspend mineral UV filters and pigments so they stay evenly distributed. This helps stabilize water-in-oil and anhydrous formulas and prevents settling.
Safety & warnings
Organically modified clays like this are used to structure the oil phase and are generally well tolerated, with low irritation potential at typical use levels. It is not a fragrance allergen and, as an inorganic clay, is not associated with comedogenicity concerns.
Origin & sourcing
Semi-synthetic; it is naturally sourced bentonite clay chemically modified with a quaternary ammonium compound.
Questions everyone asks
Why is quaternium-18 bentonite used in mineral sunscreens?
It thickens the oil phase and keeps mineral UV filters and pigments evenly suspended so they do not settle.
Is it a natural clay?
It starts as natural bentonite clay but is chemically modified to make it work in oil-based formulas, so it is best described as semi-synthetic.