CD04 Hydroquinone allergic contact dermatitis: widening the potential dangers of black henna tattoos

Abstract A 35-year-old woman presented with a 1-year history of severe facial dermatitis. She had a previous significant black henna tattoo reaction at age 6 years, followed by a reaction to hair dye aged 14 years, when allergic contact dermatitis (ACD) to para-phenylenediamine (PPD) was confirmed by patch testing. Her skin had been clear until use of a facial cream to treat melasma, containing tretinoin, fluocinolone and 4% hydroquinone. She had purchased this from an online personalized skincare prescription service (Dermatica®). Patch testing to the British Society for Cutaneous Allergy baseline (excluding PPD), medicament, facial and methacrylate series, hydroquinone 1% and the patient’s own products revealed positive reactions to the Dermatica® product (day 2 ++, day 4 ++), hydroquinone 1% (day 2 +, day 4 ++) and tert-butylhydroquinone (day 2 −, day 4 +). In the absence of reactions to any other constituents of the Dermatica® cream, we concluded that hydroquinone was the responsible allergen. The risk of crossreactivity between PPD and other aromatic amines such as para-toluene­diamine and azo dyes is well known. The chemical structure of hydroquinone is also closely related to PPD; both compounds consist of a benzene ring with respective hydroxyl or amino groups located in the same 1 and 4 para-positions. Theories to explain the crossreactivity between PPD and its related aromatic amine compounds suggest the generation of a common metabolic product such as benzoquinone, which may more readily form complexes that activate the sensitization process (Pot LM, Scheitza SM, Coenraads PJ, Blömeke B. Penetration and haptenation of p-phenylenediamine. Contact Dermatitis 2013; 68: 193–207). We propose that our patient developed ACD to hydroquinone due to this crossreactivity and her established PPD allergy. ACD secondary to skin-lightening creams may occur due to preservative ingredients; however, as in our case it can be caused by hydroquinone itself. Due to its antioxidant and stabilizing properties, hydroquinone can also be found in hair dye, rubber, adhesives, photographic developers and dental prostheses. The frequency of positive patch test reactions to hydroquinone in patients with suspected ACD has been reported as 0.3% (DeKoven JG, Warshaw EM, Zug KA et al. North American Contact Dermatitis Group patch test results: 2015–2016. Dermatitis 2018; 29: 297–309). Given the increasing accessibility to hydroquinone lightening creams online, we would like to highlight this source of ACD and potential crossreactivity with PPD. Public health campaigns warn of the dangers of black henna tattoos and caution those with a history of reactions to avoid use of permanent hair dyes. We propose that education for these patients should go further, with the additional advice to avoid use of hydroquinone products.