What it is
This ingredient is a crosslinked acrylic polymer closely related to carbomer, the very common water-loving thickener, but it additionally contains long-chain (C10-30) alkyl acrylate monomers that are hydrophobic. This dual water-loving and oil-loving character lets it thicken water phases while also helping to stabilize emulsions that contain oils, which is useful in gel-cream and fluid sunscreen textures. Like other polyacrylic acid polymers, it builds viscosity by swelling once the formula is neutralized to a suitable pH.
Safety & warnings
Large crosslinked acrylate polymers are not meaningfully absorbed by skin and are widely used in leave-on and rinse-off products, including those for sensitive skin. They function mainly as inert structural agents in the formula rather than as actives, and irritation attributable to the polymer itself is uncommon.
Origin & sourcing
It is a fully synthetic polymer made by free-radical copolymerization of acrylic acid with long-chain alkyl acrylate monomers, crosslinked into a network. The crosslinked polyacrylic acid family is produced industrially and supplied as a dry powder that is dispersed and neutralized in the formula.
History
Crosslinked polyacrylic acid thickeners were commercialized under the Carbomer name and are produced by free-radical polymerization; the alkyl-modified crosspolymers were later developments that added hydrophobic monomers to extend the family's usefulness in formulas containing oils.
Questions everyone asks
What is this ingredient for in sunscreen?
It thickens the water phase and helps keep oils and other ingredients evenly suspended, giving lotions and gel-creams a stable, smooth texture.
Is it the same as carbomer?
It is closely related to carbomer but also carries hydrophobic alkyl groups, which make it better at stabilizing formulas that contain oils.
Does it absorb into skin?
No. It is a large crosslinked polymer that stays on the surface and acts as a texture and stability agent.