Relevance of positive patch-test reactions to cocamidopropyl betaine and amidoamine.

BACKGROUND: Cocamidopropyl betaine (CAPB) is a surfactant, primarily used in personal cleansing products, that may cause allergic contact dermatitis (ACD). Amidoamine (AA), a by-product and a known contaminant in CAPB synthesis, may be the true allergen responsible for some cases of CAPB allergy. Co-reactivity with these allergens and cocamide diethanolamine (CDEA) and formaldehyde has been noted anecdotally. OBJECTIVE: This study investigated (1) the correlation and clinical relevance of positive patch-test reactions to CAPB and AA in cases of ACD and (2) the rate of positive reactions to CDEA and formaldehyde in these patients. METHODS: Patients with patch-test reactions to either CAPB or AA during 2001 were retrospectively identified. Relevance of reactions to CAPB and AA was then graded as definite, probable, or not relevant, based on patient follow-up. The proportion of these patients who also had positive reactions to CDEA or formaldehyde was noted. RESULTS: Of 957 patch-tested patients, 49 had positive reactions to either CAPB (42.9%) or AA (34.3%) or to both (22.8%). Of these patients, 35 were available for follow-up. Twenty-nine (83.0%) of these patients identified the surfactant in their home products. In all of these patients, the dermatitis was felt to be due in whole or in part to CAPB exposure. Two patients (5.7%) had a positive reaction to CDEA, and 8 patients (23%) had a positive reaction to formaldehyde. CONCLUSION: Patch testing with both CAPB and AA identifies patients with ACD relevant to exposure to CAPB. Since few patients react to both allergens, testing with both separately is useful. Formaldehyde allergy was overrepresented in CAPB-allergic patients in this series of patients.