CD18 Concomitant dye sensitization in patients with para -phenylenediamine allergy: a retrospective patch test study

Abstract

para-Phenylenediamine (PPD) is a well-recognized cause of allergic contact dermatitis (ACD), most commonly from hair dyes and temporary black henna tattoos. PPD is included in the British standard series, but other hair dye chemicals are not routinely tested, so concomitant sensitization may go unrecognized. The aim of this study was to determine the prevalence of PPD allergy in a patch-tested cohort and assess sensitization to alternative hair dye chemicals, with implications for the safety of products marketed as ‘PPD-free’. Patch test results from June 2014 to January 2023 were reviewed. Patients positive to PPD 1% were assessed for reactions to toluene-2,5-diamine sulfate (DATS), 3-aminophenol and 4-aminophenol. Hair dye and black henna exposure were recorded. An online search of hair dye products marketed as ‘PPD-free’ was undertaken to review ingredient labelling. Of 3958 patients tested, 114 (2.9%) were PPD positive. Among 112 patients tested to alternative allergens, 31 (27.7%) reacted to DATS, 23 (20.5%) to 3-aminophenol and 23 (20.5%) to 4-aminophenol, with 37 patients (33.0%) sensitized to one or more of these chemicals. Hair dye exposure was reported by 75.4% and black henna use by 21.1%. Online review of ‘PPD-free’ hair dye products showed that some contained alternative aromatic amines. In one survey of 51 PPD-free products, around 10% listed PPD as an ingredient, while others contained related sensitizing chemicals. ACD to PPD is common, and concomitant sensitization to other hair dye chemicals is frequent. Many individuals allergic to PPD remain at risk despite using ‘PPD-free’ products. Patients should be counselled to read ingredient lists carefully, as avoidance of PPD alone may be insufficient.