Contact sensitization to hair colours in acquired dermal macular hyperpigmentation: results from a patch and photo‐patch test study of 108 patients

Background Acquired dermal macular hyperpigmentation (ADMH) is an umbrella term including lichen planus pigmentosus, erythema dyschromicum perstans and pigmented contact/cosmetic dermatitis. Objective To establish contact sensitization to hair colours as an aetiological factor for ADMH. Methods Detailed clinical examination, skin biopsies, and patch and photo‐patch testing with Indian standard series and patient's own cosmetic products were performed. Results Thirty‐nine (36.1%) patients were found to demonstrate a positive patch/photo‐patch test with 35/39 reacting to their own products (all were hair colours) and 16/39 reacting to antigens from commercial series (commonly paraphenylenediamine). Fourteen patients developed delayed hyperpigmentation on positive patch‐test sites at 1 month. Higher mean age, symptomatic pigmentation (pruritus, burning and photosensitivity), hair margins involvement (outer surface, helix and lobule of ear; temples and preauricular area), ill‐defined lesions, epidermal atrophy and epidermal melanization extending >3 layers were significantly common in patch‐test‐positive patients. Well‐defined lesions, perioral involvement and associated lichen planus were clinical pointers towards patch‐test negativity. Conclusion Index study exemplifies that patch‐test results have distinct clinical and histopathological correlates in ADMH. Hair dye contact sensitization appears to be an important aetiological factor in about one‐third patients presenting with ADMH.