Quaternium-91

Quaternium-91 is a synthetic quaternary ammonium compound—a type of conditioning polymer commonly used in hair care products. It belongs to a class of ingredients designed to improve the texture and manageability of hair fibres by depositing a protective layer on the hair shaft.Whilst quaternium compounds have a long history in cosmetic formulations, Quaternium-91 is relatively uncommon in skincare products, appearing in less than 0.1% of formulations. Its primary function is hair conditioning rather than treating skin concerns.

Quaternium-91 works by adhering to the outer layer of hair fibres through electrostatic attraction. Hair has a negative charge, and this positively charged polymer deposits onto the surface, creating a smoother, more ordered layer. This coating reduces friction between fibres, which improves combability and reduces mechanical damage during styling.The conditioning film also helps seal moisture within the hair shaft and can improve the overall appearance of shine and smoothness by creating a more uniform surface texture.

Quaternium-91 is most effective when used in rinse-off conditioners, leave-in treatments, or styling products where it can remain on hair long enough to provide conditioning benefits. In rinse-off products, allow sufficient contact time (2-3 minutes) for optimal conditioning. If used in skincare products, follow the product instructions, though benefits will primarily be cosmetic rather than therapeutic for skin.

Quaternium compounds are well-established in cosmetic use and generally well-tolerated on both skin and hair. As with any conditioning agent, it may build up on hair with repeated use if not regularly clarified with a clarifying shampoo.