Cross‐elicitation responses to 2‐methoxymethyl‐ p ‐phenylenediamine under hair dye use conditions in p ‐phenylenediamine‐allergic individuals

Summary Background The factors influencing elicitation responses in individuals allergic to p ‐phenylenediamine ( PPD ) in hair dyes are not well understood. Objectives Investigation of the elicitation response to the new, less‐sensitizing PPD alternative 2‐methoxymethyl‐ p ‐phenylenediamine ( ME ‐ PPD ) under simulated hair dye use conditions. Methods The cross‐elicitation response to ME ‐ PPD (2% in a hair dye test product for 30 min on forearm then rinsing) was analysed at days 2 and 3 in 30 PPD ‐allergic individuals with diagnostic patch test grades +, ++ or according to the classification of the International Contact Dermatitis Research Group. Results Cross‐reactivity to the ME ‐ PPD ‐containing hair dye test product was elicited in nine of 30 subjects (30%), while 70% were negative. Cross‐reactivity was elicited in two of four cases with grade , three of 10 with grade ++ and four of 16 with grade +. Under identical conditions, PPD was previously found to elicit a response in 21 of 27 PPD ‐allergic individuals. In 18 of these 21 individuals, either the strength of the cross‐elicitation response to ME ‐ PPD was decreased or no response occurred. Conclusions Under simulated hair dye use conditions, a significantly lower degree of cross‐elicitation to ME ‐ PPD (30%) was observed than previously reported for PPD (32 of 38, 84%). Additionally, a decreased cross‐elicitation strength was observed across all three patch test grades, likely reflecting the reduced skin‐sensitization properties of ME ‐ PPD . Consequently, careful dermatological evaluation is required to assess cross‐reactivity to ME ‐ PPD in patients allergic to hair dyes.