Paraphenylenediamine Contact Allergy and Post-Diagnostic Outcomes: A Single-Centre Study From the United Kingdom.

BACKGROUND

Paraphenylenediamine (PPD) is a potent allergen, frequently responsible for allergic contact dermatitis (ACD) from hair dyes and temporary 'black henna' tattoos. Misleading 'PPD-free' labelling may expose sensitised individuals to structurally related aromatic amines.

OBJECTIVES

To characterise clinical features, cross-reactivity and outcomes of patients diagnosed with PPD ACD following diagnosis of PPD allergy, and to evaluate the accuracy and safety of 'PPD-free' products marketed in the United Kingdom.

METHODS

Retrospective study of PPD positivity between 2018 and 2025 at a university hospital was conducted. Demographic, clinical and exposure data were extracted from records, and outcomes post-diagnosis were surveyed by telephone. Ingredient lists of permanent 'PPD-free' hair dyes/tints identified through a structured online search were reviewed for cross-reactive amines.

RESULTS

Of 1306 patients tested for PPD over 7 years, 56 (4.3%) had a positive reaction. The mean age of affected patients was 49 years; 82% were female, and hair dye was the most frequently reported source of exposure (77%). Eight (14%) had occupational exposure. Among 37 tested to para-toluenediamine (PTD), 10 (27%) were positive. Among 31 followed up, 24 (77%) reported remission after avoidance. Only 1 of 10 permanent 'PPD-free' hair dyes/tints examined was found to be free of any potentially cross-reactive amines.

CONCLUSIONS

PPD remains a prevalent allergen causing chronic and occupational ACD. 'PPD-free' products frequently contain cross-reactive amines, highlighting the need for improved labelling and careful counselling.