What it does
The EU's CosIng database gives its chemical name as docosyltrimethylammonium chloride, a quaternary ammonium salt, and lists three functions: antistatic, hair conditioning and preservative.1 In a conditioner it is there for the first two; the EU defines hair conditioning as leaving hair easy to comb, supple, soft and shiny.2 Cationic surfactants are considered the backbone of a conditioner: their positive charge draws them to the negatively charged surface of hair, where they deposit, especially on weathered or damaged areas, reduce static and make combing easier.3
In a 2026 laboratory comparison of four cationic surfactants, it deposited most and cut wet combing force most, which the authors credit to its long 22-carbon chain and its small chloride ion4; the Behentrimonium Methosulfate page has the details.
The preservative function is why "Keeps the formula fresh" comes first among the roles further down this page: they are taken from the EU database, which records every listed function without saying which one matters. The compound is indeed permitted as a preservative in small amounts, but that is a separate use with its own, much lower limit, set out below.
The EU rules, entry by entry
| Entry | Use | Product type | Maximum in the ready-to-use product |
|---|---|---|---|
| Annex III, entry 287 | Any purpose other than preserving the product | Rinse-off hair products | 5.0% |
| Annex III, entry 287 | Any purpose other than preserving the product | Leave-on hair products | 3.0% |
| Annex III, entry 287 | Any purpose other than preserving the product | Leave-on face products | 3.0% |
| Annex V, entry 44 | Preservative | Not restricted by product type | 0.1% |
Under entry 287, each percentage applies to behentrimonium chloride alone or to its sum with Cetrimonium Chloride and steartrimonium chloride, while those two must also stay within their own combined limits in entry 286. The purpose other than preserving has to be apparent from the presentation of the product. Entry 44 covers alkyl (C12-22) trimethyl ammonium bromides and chlorides, behentrimonium chloride among them.5
Why the limits look like this
The conditioning limits date from 2014. The EU's scientific committee had evaluated cetrimonium, steartrimonium and behentrimonium chloride for uses other than preserving in 2005, 2007 and 2009, and concluded that, apart from the potential of quaternary ammonium formulations to irritate skin, especially when these compounds are combined, they do not pose a risk to consumers below set limits. To allow for that irritation potential, the Commission capped the sums of the substances, and applied the committee's limits for leave-on face creams to all leave-on face products.6
The committee's 2009 opinion accepted the levels the industry dossier proposed for behentrimonium chloride: up to 5.0% in rinse-off hair products and 3.0% in leave-on hair and facial cream products. In rabbit tests the three compounds appeared to cause irreversible eye damage above 8%; diluted to 5%, behentrimonium chloride caused persistent irritation of the conjunctiva, and at 3% some irritation. The committee read the few positive results in skin sensitisation studies as irritation rather than allergy.7
How it appears on a label
As Behentrimonium Chloride, its name in the EU glossary.8 A label gives no concentrations, so it cannot show how close a product comes to any of these limits. Cetrimonium Chloride and steartrimonium chloride are counted together with it under entry 2875, while Behentrimonium Methosulfate has no annex entry at all. The conditioner ingredients guide compares the three in a table, and the hair product scanner shows the role of every name on a list.