Cross‐elicitation responses to 2‐methoxymethyl‐p‐phenylenediamine in p‐phenylenediamine‐allergic individuals: Results from open use testing and diagnostic patch testing

BACKGROUND: Allergic contact dermatitis caused by p‐phenylenediamine (PPD) is a health concern for hair dye users. Because of its lower sensitization potency, the PPD derivative 2‐methoxymethyl‐p‐phenylenediamine (ME‐PPD) has been developed as an alternative hair dye for primary prevention. However, cross‐elicitation responses can occur in PPD‐allergic subjects. OBJECTIVES: To compare cross‐elicitation responses to ME‐PPD in open use and diagnostic patch testing of PPD‐allergic subjects with hair dye‐related allergic contact dermatitis. METHODS: Reactions to ME‐PPD were investigated in 25 PPD‐allergic subjects by performing (1) 45‐minute open use testing with a hair dye containing 2.0% of either ME‐PPD or PPD, and (2) patch testing with increasing ME‐PPD concentrations (0.1%–2.0% pet.). RESULTS: Of the 25 PPD‐allergic subjects, 21 (84%) reacted to open use testing with a hair dye containing 2.0% PPD, and testing with 2.0% ME‐PPD led to cross‐elicitation in 12 (48%). When patch tested with increasing ME‐PPD concentrations, 13 (52%) cross‐reacted at 0.1% (lowest dose) and 21 (84%) at 2.0% (highest dose), indicating decreased reactivity as compared with published PPD dose‐response data. CONCLUSION: In line with the decreased cross‐reactivity of ME‐PPD in hair dye open use testing, PPD‐allergic subjects show an attenuated cross‐elicitation dose response to ME‐PPD in patch testing.