What is it?
A synthetic polymer made from acrylic acid, methacrylic acid or their simple esters and neutralized with sodium. In water it builds thickness, and as it dries it forms a thin film. It is used to thicken and stabilize lotions, creams and gels, to bind powders and to help makeup, including eye makeup, form a film. It is a close chemical relative of sodium polyacrylate and carbomer.
Key information
- The CIR Expert Panel concluded in its 2018 re-review that sodium acrylates copolymer is safe as used in cosmetics when formulated to be non-irritating.
- Like other acrylic polymers, it can contain small amounts of leftover monomer, which the CIR said manufacturers should keep to a minimum.
- Acrylic acid polymers break down slowly in the environment, a question outside the CIR's safety review.
- The Foundation rates the closely related sodium polyacrylate Red Light.
More information
Sodium acrylates copolymer is closely related to sodium polyacrylate, the sodium salt of polyacrylic acid, and the Cosmetic Ingredient Review (CIR) lists the same CAS number for both. Like other polymers built from small units called monomers, it can contain traces of unreacted monomer.
The CIR Expert Panel reviewed it with 125 other acrylates copolymers, including sodium polyacrylate and carbomer, and concluded in its 2018 re-review that they are safe as used when formulated to be non-irritating. In 2018 it was reported in 179 products, at up to 18 percent in leave-on products. Because these polymers are large, the Panel did not expect significant absorption through the skin, and the data showed no potential to cause skin allergy. The Panel asked manufacturers to keep residual monomer to a minimum; in an earlier industry survey, residual acrylic acid was typically 10 to 1,000 parts per million. It also said these polymers should not be made in benzene.
Environmental effects were not part of the CIR review. A 2021 review funded by a German cosmetics industry association found that acrylic acid polymers biodegrade slowly but are expected to be largely removed in wastewater treatment, are too large and charged to build up in aquatic life, and show little toxicity; the authors called that conclusion preliminary. The EU's 2023 microplastics restriction targets solid, insoluble synthetic polymer particles. It excludes polymers that dissolve in water above 2 grams per liter and particles that lose their particle form in use, for example by swelling or forming a film, so whether an acrylic thickener is covered depends on its form.
Reality check: on skin, sodium acrylates copolymer has a clean safety review. The open questions are leftover monomer, which labels do not show, and persistence after it washes down the drain.
Sources: Cosmetic Ingredient Review: Amended safety assessment of acrylates copolymers as used in cosmetics (2018 review, draft final report); Environmental Sciences Europe (2021): Environmental fate and effects of water-soluble synthetic organic polymers used in cosmetic products; EUR-Lex: Commission Regulation (EU) 2023/2055 restricting synthetic polymer microparticles
