Elicitation of the immune response to p-phenylenediamine in allergic patients: the role of dose and exposure time

Summary Background Usage of hair dye products containing p‐phenylenediamine (PPD) is a concern for PPD‐allergic individuals. Objectives The present study investigates the role of dose and exposure time on elicitation of allergic contact dermatitis under conditions of permanent hair dyeing. Methods Elicitation responses after application of a typical hair dye product containing 2% PPD for 30 min followed by rinsing were analysed in 38 PPD‐allergic individuals with a documented history of hair dye‐related allergy. Skin binding experiments in vitro were performed to distinguish the dose available for elicitation from the dose applied. Results A positive reaction was elicited in 20 of 20 patients with grades ++ to +++ and 12 of 18 with grade + according to the classification of the International Contact Dermatitis Research Group. Under conditions of diagnostic patch testing (48 h exposure), the dose available for elicitation is more than 10‐fold higher compared with the dose available for hair dyeing (30‐min exposure, rinsing of product). Conclusions This investigation demonstrates that under simulated hair dye use conditions the actual exposure to PPD is more than an order of magnitude lower than under diagnostic patch testing, although sufficient to elicit a clearly noticeable reaction in 84% of PPD patch test‐positive individuals.