While this is not an exhaustive list, here are some common chemicals named in the recent state bans, as well as ones that are frequently flagged by researchers and consumer advocacy groups. These chemicals appear on the ingredients lists of products containing them.
Butylated hydroxyanisole (BHA)
What it is: BHA is commonly used as a preservative in personal care products that contain oils or fats, such as lipsticks, eyeliners and moisturizers.
What the research says: Studies in rats (the findings of which do not always apply to humans but can suggest areas for human research) have linked BHA to stomach cancer, damage to kidney cells, and to the development of reproductive systems in males and females.
Several groups consider it a potential human carcinogen, including the World Health Organization’s International Agency for Research on Cancer, the U.S. National Toxicology Program, and the California Office of Environmental Health Hazard Assessment, which compiles the state’s Proposition 65 list of harmful chemicals that businesses must warn customers about. Its relative, butylated hydroxytoluene, or BHT, is considered slightly less toxic but has also been flagged for regulation in Europe and Japan.
Coal tar dyes like m-, o- and p-phenylenediamine
What it is: Coal tar is a thick brown-black liquid. M-phenylenediamine, o-phenylenediamine and p-phenylenediamine are compounds that were originally derived from coal tar and are now often produced synthetically. They are frequently found in hair dyes. The darker the dye, the more phenylenediamine it typically contains.
What the research says: Coal tar dyes may cause allergic reactions or skin irritation that can result in hair loss. Epidemiological data has also linked some coal tar dyes to an increased risk of developing non-Hodgkin’s lymphoma, multiple myeloma, acute leukemia and bladder cancer. Products containing more than trace amounts of m- and o -phenylenediamine will be banned in California and Maryland in 2025.
Diethanolamine (DEA)
What it is: DEA is part of a group of chemicals frequently used as emulsifiers in products that are creamy or foamy, like shampoos and shaving creams. Its relatives include monoethanolamine (MEA) and triethanolamine (TEA).
What the research says: These compounds often react with other preservatives in personal care products to form nitrosamines, which are chemicals that the International Agency for Research on Cancer and the U.S. National Toxicology Program identify as “reasonably anticipated to be a human carcinogen.” Because of the potential for this reaction, DEA is prohibited in cosmetics in Europe and Canada and consumer advocates recommend avoiding other ethanolamines as well.
Formaldehyde and formaldehyde-releasers
What it is: Formaldehyde is a strong-smelling chemical that is used to lengthen the shelf-life of some cosmetics, hair straighteners and nail polishes. Some companies have started moving away from formaldehyde use, but other preservatives that prevent the growth of bacteria in water-based personal care products — like shampoos and liquid baby soaps — can still release formaldehyde gas over time. These include DMDM hydantoin, diazolidinyl urea, glyoxal, sodium hydroxymethylglycinate and quaternium-15.
What the research says: Exposure to low levels of formaldehyde fumes is known to irritate the eyes, nose and throat, while higher exposures, particularly over longer periods of time, have been linked to nose and throat cancers as well as other ailments in certain workers, such as hair stylists and manicurists. Formaldehyde, paraformaldehyde and quaternium-15 are included in California and Maryland’s bans.
Fragrance
What it is: Fragrance formulas are considered trade secrets, which means companies can hide any number of chemical ingredients under the umbrella terms “fragrance” or “parfum.” A product’s label can say “unscented” and still have one of these terms in the ingredient list because some fragrance compounds may be used as dyes, solvents or stabilizers for active ingredients or for masking other undesirable smells in a product.
