Formulation base
Behentrimonium Methosulfate
INCI: Behentrimonium Methosulfate · also BTMS, behenyl trimethyl ammonium methosulfate, cationic conditioner
The cationic conditioning agent in most rinse-out conditioners worth using. Derived from rapeseed or colza oil, with a 22-carbon chain, which is unusually long for this class and is why it deposits well.
Why it is here
The part of Human Condition that does the conditioning: not a sulfate despite the name, not a plastic, just the reason a comb goes through.
Damaged and washed hair carries a negative surface charge, more so where the cuticle is worn. A positively charged surfactant is attracted to exactly those sites and adsorbs there, laying down a thin lubricating layer. The result is measurably lower combing force and less mechanical damage when you drag a comb through wet hair. It changes the surface. It does not rebuild the fiber.
The receipt
Longer-chain cationics behentrimonium methosulfate and behentrimonium chloride outperformed the shorter-chain CTAC and STAC on deposition and conditioning; wet combing force fell most with behentrimonium chloride, and ATR-FTIR showed no reversal of oxidative damage, indicating conditioners improve manageability without repairing structural damage.
Electrokinetic analysis reveals common conditioner ingredient interactions with human hair. International Journal of Cosmetic Science, 2026. in vitro. PMID 41126531
In practice
- Typical use
- 1 to 5 percent in a rinse-out conditioner, usually supplied as BTMS-25 or BTMS-50 pellets at 2 to 7 percent of the formula depending on the grade.
- Pairs with
- Cetearyl Alcohol, Panthenol, Hydrolyzed Protein
- Keep apart from
- Anionic surfactants in the same product: cationic and anionic surfactants form complexes and cancel each other out. This is why a conditioner is a separate step from a shampoo rather than a bolt-on to one.
- Cautions
- None notable. It is a rinse-out ingredient with a long safety record and low irritation potential relative to older quaternary compounds. Not a plastic, and it does not build up the way silicones can.
Questions people ask
Does conditioner actually repair damaged hair?
No, and the honest version of that answer is in the data. In the 2026 electrokinetic study, cationic conditioners significantly improved wet combing and manageability, but infrared analysis showed no reversal of oxidative damage to the fiber. Hair is dead keratin. Conditioner makes it behave better and stops further mechanical damage. That is a real job.
What makes behentrimonium methosulfate different from other conditioning agents?
Chain length. Behentrimonium has a 22-carbon tail, longer than the 16 carbons of cetrimonium compounds, which means stronger van der Waals interaction with the hair surface and better deposition. In head-to-head electrokinetic testing the long-chain behentrimonium compounds beat the shorter cetrimonium and stearalkonium ones on both deposition and combing.
Is it a sulfate?
No. The methosulfate is a counterion, the negatively charged partner to the positively charged conditioning molecule, not a sulfate detergent. It makes up a fraction of the ingredient and does none of the cleaning, because nothing here is cleaning. The naming genuinely is confusing and the confusion is not your fault.