Is cocamidopropyl betaine a contact allergen? Analysis of network data and short review of the literature.

BACKGROUND

There is no general agreement on whether cocamidopropyl betaine (CAPB) is a skin sensitizer.

OBJECTIVE

To examine the evidence for CAPB being a (non-)sensitizer.

METHODS

This was a retrospective analysis of data on patch testing with CAPB 1% aqua collected by the Information Network of Departments of Dermatology from 1996 to 2009, with a focus on the patch test reaction profile, and demographic and clinical features of CAPB positives, supplemented by a literature review.

RESULTS

Eighty-three thousand eight hundred and sixty-four patients were patch tested with CAPB 1% aqua, yielding 2.16% [95% confidence interval (CI) 2.06-2.26%] positive (2.03% + and 0.13% + + /+ + + ) and 4.6% non-allergic reactions. Thus, the reaction index was-0.368 and the positivity ratio was 94.2%. Reproducibility on synchronous patch testing (n = 6534) was poor [Cohen's kappa: 0.29 (95% CI 0.25-0.32)] and results upon retesting (n = 1157) were almost non-reproducible [kappa: 0.12 (95% CI 0.05-0.19]. Multifactorial logistic regression analysis revealed an increased risk associated with being male and aged ≥40 years, with atopic dermatitis, with scalp dermatitis, with being a hairdresser, and with a 48-hr patch test application. When only + + or + + + reactions were used as a conservative outcome, only the elevated risk in males and in patients with atopic dermatitis remained significant.

CONCLUSION

The vast majority of positive reactions to CAPB are presumably false positive. Allergic reactions are very rare. This would support the notion of CAPB being 'not a significant skin sensitizer', in line with current classification systems.