LAUSR

Abstract This work aims to determine the roles of reactive oxygen species HO· and HO2‐ in the bleaching of melanins by alkaline hydrogen peroxide. Experiments using melanosomes isolated from human hair indicated that the HO· radical generated in the outside solution does not contribute significantly to bleaching. However, studies using soluble Sepia melanin demonstrated that both HO2‐ and HO· will individually bleach melanin. Additionally, when both oxidants are present, bleaching is increased dramatically in both rate and extent. Careful experimental design enabled the separation of the roles and effects of these key reactive species, HO· and HO2‐. Rationalisation of the results presented, and review of previous literature, allowed the postulation of a simplified general scheme whereby the strong oxidant HO· is able to pre‐oxidise melanin units to o‐quinones enabling more facile ring opening by the more nucleophilic HO2‐. In this manner the efficiency of the roles of both species is maximised. Graphical abstract Figure. No Caption available. HighlightsThe roles of oxidants in the mechanism of hair melanin bleaching are proposed.Both hydroxyl radical and perhydroxyl anion contribute to melanin bleaching.Hydroxyl radicals pre‐oxidise melanin facilitating reaction with perhydroxyl anion.Ammonia plays no role in bleaching beyond melanin solubilisation and pH control.