Encyclopedia · conditioning agent
Behentrimonium chloride
A long-chain, positively charged conditioning ingredient that clings to hair and detangles it, with good lab evidence for smoothing and none for repair.
What it is
A quaternary ammonium salt with a 22-carbon (behenyl) tail. Combined with fatty alcohols it forms the creamy gel of most rinse-off conditioners. It is a cosmetic ingredient in the US, EU and UK, not a drug.
How it works
Hair is net negative at normal product pH, so the positive head group is attracted and the long tail sticks out and lubricates. See how conditioner works.
What the studies show
- In a 2026 Singapore study using streaming potential and wet combing, behentrimonium chloride deposited better and cut combing force more than behentrimonium methosulfate, the C16 cetrimonium chloride and stearalkonium chloride. Infrared analysis showed "no reversal of oxidative damage". Tham 2026
- Conditioner gels made with behentrimonium had the highest structural strength, which affects wet combing. This is formulation-lab work. Davies 2020
- Behentrimonium chloride served as the reference cationic surfactant in electrokinetic tests of cationic guar, from a polymer supplier. McMullen 2021
- We found no independent human trial on breakage or hair health. The benefit is real but cosmetic.
How it's used in studies
Formulation levels are not given in the abstracts we opened. EU limits are 5.0% in rinse-off and 3.0% in leave-on hair products (Regulation 2014/866).
Side effects and safety
Quaternary ammoniums are skin and eye irritants at high concentrations, which is why the EU limits exist. Contact allergy is uncommon. Keep it out of your eyes.
Bottom line
A good sign in the ingredient list of any conditioner meant to detangle. The claim that behentrimonium is a "harsh chemical" is not supported at cosmetic levels. It suits all hair types, most obviously coarse, curly or damaged hair, and it is cheap. We are confident that it conditions and equally confident that it does not repair.
Fun facts
The chloride salt beat the methosulfate in head-to-head testing, though most products use the cheaper, easier-to-process methosulfate. Tham 2026
Studies 3
Tham HP et al. Electrokinetic analysis reveals common conditioner ingredient interactions with human hair. Int J Cosmet Sci. 2026
Tested: behentrimonium chloride and methosulfate, cetrimonium chloride, stearalkonium chloride
Result: Longer-chain behentrimonium chloride cut wet combing force and deposited best; none reversed oxidative damage.
Read the study ↗Davies AR, Amin S. Microstructure design of CTAC:FA and BTAC:FA lamellar gels using an automated formulation platform. Int J Cosmet Sci. 2020
Result: Gel structure strength was highest for behentrimonium systems, peaking at a surfactant to fatty alcohol ratio of 6:10, and it affected wet combing.
Read the study ↗McMullen RL et al. Investigation of the interactions of cationic guar with human hair by electrokinetic analysis. Int J Cosmet Sci. 2021
Tested: cationic guar compared with behentrimonium chloride and polyquaternium-28
Result: Guar molecular weight set adsorbed layer thickness and charge density set surface charge; anionic surfactant sorption was quicker on African, grey European and mixed hair than on Chinese, dark European and Indian hair.
Read the study ↗Related
- Behentrimonium methosulfateThe methosulfate salt of the same C22 conditioning ingredient as behentrimonium chloride, slightly weaker in head-to-head lab testing.
- Cetrimonium chlorideA shorter-chain conditioning ingredient, a bit less effective than the behentrimonium salts but lighter, found in many shampoos, light conditioners and sprays.
- Cetearyl alcoholA waxy blend of cetyl and stearyl alcohols that thickens conditioners and builds the gel that carries the conditioning agent; despite the name, it is not a drying alcohol.
- Behenyl alcoholThe longest common conditioner fatty alcohol, a stiff wax that gives rich, thick conditioners; it has no hair-specific studies.
- Polyquaternium-10A positively charged cellulose polymer that coats hair during shampooing, easing wet combing and helping deliver silicones, with some build-up risk.
- How conditioner worksRinse-off conditioner coats hair with a positively charged layer that cuts friction and tangling; it does not repair structural damage.