Extreme patch test reactivity to p-phenylenediamine but not to other allergens in children.

Background: According to clinical impression, extreme patch test reactions (+++) to p-phenylenediamine (PPD) are not uncommon in children.
Objectives: To investigate the patch test reactivity in children (aged 1-14 years) in comparison with other age groups and other allergens.
Methods: A retrospective analysis was performed of data from the German Information Network of Departments of Dermatology, including all patients consecutively patch tested between 1994 and 2004 with PPD, and, for comparison, nickel, fragrance mix I, and methylchloroisothiazolinone (MCI)/methylisothiazolinone (MI). The distribution of +, ++ and +++ grades of positive reactions among those with a positive reaction were analysed in five age strata.
Results: We found a strikingly higher proportion of +++ reactions to PPD in children than in all other age groups (p < 0.001). No such difference was observed for the other allergens. The main suspected exposures associated with extreme reactions to PPD in children were hair dyes and 'henna tattoos'.
Conclusions: The high proportion of extreme patch test reactions to PPD, but not to other important allergens, in children reflects intense sensitization, probably because of a high induction dose from PPD-containing 'henna tattoos'. In children with a history of contact allergy to 'henna tattoos' or hair dyes, the standard patch test concentration of PPD 1% should be drastically reduced.
(© 2011 John Wiley & Sons A/S.)