Contact Allergens in "PPD-Free" Hair Dyes

Background: Hair dyes are a commonly used cosmetic product and an important cause of allergic contact dermatitis (ACD). Primary hair dye agents, paraphenylenediamine (PPD) and other aromatic amines, are potent contact sensitizers. Despite some hair dyes being advertised as all natural or allergen-free, patients still present with hair dye contact allergy following the use of these products. We hypothesized that these products may contain cross-reactive ingredients not tested on standard series or undisclosed ingredients such as trace amounts of the allergens.Objective: We aimed to test hair dyes marketed and sold in the United States as "PPD-free" for the presence and quantity of common hair dye allergens and ingredients, including p-phenylenediamine, m-aminophenol, p-aminophenol, toluene-2,5-diamine sulfate, 2-nitro-p-phenylenediamine, and 2-hydroxy-1,4-naphthoquinone.Methods: We tested best-selling hair dyes advertised as "PPD-free" for common allergens through high-performance liquid chromatography coupled to high-resolution mass spectrometry.Results: In 7 out of 51 hair dye products, we detected a compound that was not present on the ingredient list. Five products contained PPD despite no mention of PPD on the ingredient list and 4 being labeled "PPD-free." One of these products contained PPD levels higher than 2% by weight, while the rest contained trace levels.Conclusions: These findings may help guide dermatologists in counseling patients with ACD about the importance of performing allergy alert testing before the use of a new hair dye product, regardless of how it is commercially advertised or labeled.