What it is
The EU's CosIng database describes Polyquaternium-10 as a cellulose ether carrying trimethylammonium groups, as a chloride, and lists two functions: antistatic and film forming.1 The EU defines the first as reducing static electricity by neutralising electrical charge on surfaces, and the second as producing a continuous film on the skin, hair or nails.2 Researchers describe it more simply as water-soluble cationic hydroxyethylcellulose.3
The number matters. The EU glossary of label names lists more than 100 numbered polyquaterniums, from Polyquaternium-1 to Polyquaternium-1174, and they are different polymers: Polyquaternium-44, for instance, is a copolymer of vinylpyrrolidone and quaternised vinylimidazolium salts5, not a cellulose. A finding about one number is a finding about that polymer.
How it conditions hair
Hair has a low isoelectric point, around pH 3.67, so in a product with a higher pH its surface carries a negative charge that draws positively charged ingredients to it.6 In tests on shampoos made with sodium laureth sulfate, every cationic polymer studied, Polyquaternium-10 among them, improved performance as judged by combing force, the feel of the hair and analytical methods, although Polyquaternium-10 did less well than a newer polymer on wet combing, lather and feel. The authors proposed that such polymers do not lie flat: they hold on at a few charged points, and the uncharged rest forms loops that reduce friction between hairs.5
Size counts more than charge. In a study that tagged Polyquaternium-10 and cationic guar with a fluorescent dye, molecular weight influenced how much polymer deposited from a shampoo base far more than its charge or the number of washes.7 Cationic polymers and a shampoo's anionic or amphoteric surfactants also form complexes called coacervates, which are thought to play an important part in how ingredients deposit.8
It changes what else stays behind. In model shampoos containing emulsified Dimethicone, the silicone deposited readily without the polymer but built up over repeated washes; with Polyquaternium-10 present, the build-up was much reduced and silicone deposition stayed roughly constant, and higher molecular weight grades deposited more silicone.3
Build-up: where sources differ
Cationic polymers can cling to hair so well that they are difficult to remove6, and a 2026 study of conditioner ingredients notes that polyquaterniums may become hard to wash off and build up over time.9 The 2000 shampoo study drew a finer line: build-up and poor removability were the most striking weaknesses of the cationic guar polymers, while Polyquaternium-10 could be removed from hair by washing with an anionic surfactant.5
A 2026 dermatology review of Afro-textured hair care lists cationic surfactants and polymers, with sulfates, silicones and mineral oils, among ingredients it says can worsen dryness and breakage, partly by promoting product build-up, without discussing each one in detail.10 The guides to curly hair shampoo ingredients and clarifying and gentle shampoos cover what that means for reading a label.
What official sources say
Polyquaternium-10 has no entry in the annexes of the EU cosmetics regulation, so no ingredient-specific EU limit or warning applies to it.11 Beyond the bottle, researchers note that it is used widely enough in hair products, lotions and makeup to reach household wastewater; in laboratory tests, activated sludge from sewage treatment bound it up to loadings far above the concentrations expected in sewage.12 In algae tests, Polyquaternium-10 materials had much lower toxicity than the more highly charged Polyquaternium-6 and -16, which the authors read as a sign that charge density is an important driver.13
How it appears on a label
As Polyquaternium-10, its name in the EU glossary.4 Nothing in the name says cellulose, so the number is the only clue to which polymer it is. In a shampoo, conditioning agents like it usually come after the cleansers, as how to read a shampoo ingredient list explains, and shampoo surfactant types sets it beside cationic guar. The shampoo ingredient checker shows what every other name on a list does.