Allergy to cocamidopropyl betaine may be due to amidoamine: a patch test and product use test study

Cocamidopropyl betaine (CAPB) is an amphoteric surfactant commonly used in personal care products and surface cleaners. Patch testing with commercially-available CAPB has yielded occasional reactions indicative of allergic contact dermatitis. To determine if subjects with previous positive patch tests would react in provocative use tests of products containing CAPB, and to study various contaminants in commercial CAPB supplies for allergenicity in these subjects, 10 subjects previously positive to CAPB on patch testing used a hair shampoo, hand soap, and body wash containing CAPB for 1-6 weeks or until a reaction developed. Later, they were patch tested to 2 different purity grades of CAPB and 3 possible manufacturing contaminants (dimethylaminopropylamine, amidoamine, and sodium monochloroacetate). 7 of the 10 subjects developed dermatitis from 1 or more CAPB-containing products at some point during the study. 9 of the 10 use-test subjects were then patch tested, and 6 of these subjects showed a reaction to amidoamine (0.1% aq.). None reacted to dimethylaminopropylamine (0.1% pet.). 1 subject reacted to CAPB but not to amidoamine. In the follow-up patch testing with CAPB that was free of amidoamine, there were no positive reactions. Most subjects who were patch-test-positive showed a reaction when using CAPB-containing skin and hair care products. The chemical amidoamine, which is used in the synthesis of CAPB and which is a known contaminant of CAPB preparations, is likely to be the actual sensitizer in most cases rather than CAPB itself. The results do not rule out the possibility that CAPB itself may be an allergen in rare cases.