Is the irritant benzalkonium chloride a contact allergen? A contribution to the ongoing debate from a clinical perspective.

BACKGROUND Benzalkonium chloride (BAC) is a well-recognized irritant. However, doubts exist that it is also a contact allergen. OBJECTIVE Analysis of clinical patch test data addressing the reaction profile and synchronous reproducibility of BAC 0.1% in petrolatum (pet.) and possible increases in risk of BAC contact allergy in certain (occupationally exposed) subgroups. PATIENTS /METHODS: Data of 42 898 patients tested with BAC 0.1% in pet. in 3 different series (topical drugs, ophthalmics, and disinfectants) in the departments of the Information Network of Departments of Dermatology (http://www.ivdk.org) between 1996 and 2006 was analysed. RESULTS Overall, morphologically 'positive' reactions were rare, 0.6-1.5%, with a total of 41 stronger positive reactions. Concordance, assessed in 3322 patients tested in duplicate, was low (kappa coefficient 0.15, 95% CI: 0-0.31). Positive test reactions were observed significantly more often in the disinfectants series compared with the 2 other series, indicating that suspected exposure to disinfectants may be associated with sensitization. However, variation of stronger BAC test positivity across potentially relevant (occupational) groups was non-significant. CONCLUSION This analysis of routine clinical data and a number of previous reports add further, if weak, evidence to the notion that BAC is a contact allergen, albeit a very rare one.