Cross-elicitation responses to 2-methoxymethyl-para-phenylenediamine in para-phenylenediamine-allergic individuals

The introduction of a methoxymethyl side chain into para-phenylenediamine (PPD) resulted in the development of a new hair dye molecule: 2-methoxymethyl-para-phenylenediamine (Me-PPD). Besides having excellent hair colouring properties, this PPD derivate has significantly lower skin-sensitizing properties than PPD and toluene-2,5-diamine. In a simulated hair dye model (i.e. open-use test), cross-reactivity to Me-PPD occurred in PPD-allergic individuals, but the number of cross-reactors was substantially lower than one would expect in an open-use test with a PPD-containing hair dye. Patch testing with Me-PPD has never been performed. The current study aimed to find the optimal patch-test concentration for detecting cross-reactivity to Me-PPD. PPD-allergic patients with a documented history of hair dye-related allergy, and different grades (+, ++, +++) of positive patch-test reactions to PPD, will be included in the study. Patch testing will be performed with Me-PPD 0.1%, 0.25%, 0.5%, 1.0% and 2.0% in petrolatum. In a simulated hair dye use model on the volar forearm, the reactivity to use concentrations of Me-PPD 2% and PPD 2% will be investigated. On the adjacent skin a similar open-use test with the same basic formula, but without Me-PPD or PPD, will be applied as a control. After 45min the hair dye will be removed from the skin surface by rinsing with water. Reading of the patch tests and the open-use tests will be performed at days 2, 3 and 7, according to the International Contact Dermatitis Research Group reading criteria. In total 30 PPD-allergic individuals will be included in this Me-PPD dose-finding pilot study. At the moment a number of individuals have been enrolled; full data will be available at the meeting.