Cocamidopropyl betaine (CAPB) may be listed on your product as cocamidopropyl, coco betaine, cocamidopropyl dimethyl glycine, cocoyl amide propyldimethyl glycine, cocoyl amide propylbetaine, tegobetaine L7, coconut oil amidopropylbetaine, and cocamido betaine. It’s a derivative of glycine betaine and cocamide. Like other amidopropyl betaines, CAPB has amphoteric properties, reacting with both acids and bases. Although derived from coconut, it’s still considered a synthetic compound.
Amidopropyl betaines have wide applications, functioning as high-foaming detergent and cleansing agents, skin conditioners, viscosity-increasing agents, surfactants (to facilitate the mixture of immiscible substances, e.g. water and oil), and co-surfactants. Whatever purpose it may serve, it’s unsafe to leave antiperspirants and products containing CAPB on your skin for longer periods especially when the concentration exceeds 3%. The problem, however, is that many products don’t list the concentration so it’s difficult to know whether the one you’re using is within the prescribed ‘safe limits’ or not.
The greatest concern you should have is that CAPB is an amine. As such, it can undergo nitrosation by reacting with some ingredients in the product you are using and produce cancer-causing nitrosamines (for more information on nitrosation and nitrosamines, see ethanolamines, aminomethyl propanol or sodium lauryl sulfate). Another concern is that it can be contaminated with amidoamine and 3-dimethylaminopropylamine and cause skin and eye irritation, sensitization or contact dermatitis. In 2004, the American Contact Dermatitis Society ‘crowned’ CAPB the Allergen of the Year in ‘honor’ of its capability to produce allergic reactions. It may interest you to know that amidopropyl betaines are environmentally toxic.