Skin irritation and sensitization potential of oxidative hair dye substances evaluated with in vitro, in chemico and in silico test methods

Permanent oxidative hair dyes are widely used but their toxicity is not well-established. Here we aimed to evaluate the skin sensitization and irritation of nine hair dye substances (MAP, MRP-N, RS, PAOX, 2,4-DAPE, 2,6-PYR, PPD, Grey HED and PM) permitted for use in EU and Korea, using in vitro and in chemico and in silico test methods. Skin sensitization was evaluated by the KeratinoSens™ assay, Direct Peptide Reactivity Assay (DPRA) and DEREK. Six of nine dyes tested were determined as sensitizers in common. However, the decision for MAP, RS or PAOX was diverged across assays showing 2 positives and 1 negative. Skin irritation of hair dye substances was assessed with or without 6% H₂O₂ on a reconstructed human epidermis, Epiderm™ which demonstrated that H₂O₂ increased the skin irritation potential of some hair dyes. PPD and PM were determined to be irritants with H₂O₂. Epidermal damages by hair dye and H₂O₂ could be further confirmed through the histology of tissue remaining after MTT assay. Collectively, our study demonstrated that hair dyes possess potential skin sensitization and irritation issues which could be further aggravated by H₂O₂.