Provocative use tests in CAPB-allergic subjects with CAPB-containing product

Cocamidopropyl betaine (CAPB) has been identified as a cause of contact allergy in personal care products. Furthermore, it has been suggested that chemicals responsible are impurities, especially dimethylaminopropylamine (DMAPA). However, skin contact concentrations with these impurities, especially DMAPA, are very low. The aim of the study was to analyse whether subjects with previous positive patch tests to CAPB would react in provocative use tests of a product containing CAPB. 10 individuals with a clinical history of contact allergy to CAPB (by positive patch test and history) took part in a ROAT which used a CAPB-based shower gel at 25% (DMAPA concentration < 1 ppm). None of the subjects showed positive allergic reactions. 1 of the test subjects did experience a flare of atopic dermatitis at the treatment site. Later, all 10 subjects were patch tested to 3 different concentrations of CAPB and DMAPA (0.1%, 0.3%, 1%) to verify the threshold that was capable of inducing a positive test reaction. 5/10 showed clear + reactions to 1% CAPB (typically at D3), whilst a further 3 gave marginal and/or irritant reactions. Only 1 of the subjects showed an allergic reaction to DMAPA. Finally, in uncontrolled use testing with the shower gel, none of the test subjects reported any adverse skin reactions. Thus, the study confirmed that CAPB-sensitive individuals can use a CAPB-based rinse-off product without the risk of experiencing an allergic reaction to CAPB.