New hair dyes prevent allergic reactions


A bad dye job is bad enough on its own, but an itchy, irritating allergic reaction is even worse. And people who become allergic to hair dyes can develop reactions to many other common substances, turning a simple cosmetic treatment into a big deal. Today, researchers who report in ACS Sustainable Chemistry & Engineering have developed a range of permanent hair colors that avoid the allergenic properties of traditional formulations.

When applied as a hair color, paraphenylenediamine (PPD) – a common ingredient in permanent hair dyes – undergoes a chemical reaction that turns the hair into a dark color that does not fade over time. This reaction, however, can also produce compounds that bind proteins in the user’s skin, causing allergic reactions, such as eczema and facial swelling. PPD can also sensitize users to other substances, including a compound commonly found in sunscreens and cosmetics, as well as common compounds in pigments and inks. Alternatives have been proposed, but they are generally not water soluble and the safety of some of the compounds is not well understood. Gopalakrishnan Venkatesan and his colleagues wanted to create new alternatives that would avoid PPD problems while providing permanent hair color.

The team prepared seven PPD-based dyes with aromatic amine ring modifications. The modifications were chosen to potentially make the compounds less reactive towards proteins and less able to be absorbed through the skin. The seven compounds permanently color the hair samples, producing a range of shades from rosy pinks to deep blacks that do not fade even after three weeks of daily washing. The team then examined the dyes in a test commonly used in the cosmetics industry to determine if a product is a skin sensitizer. Five of the modified dyes were “weak” sensitizers, while the PPD was “moderate”. Another test showed that the new compounds generated a reduced inflammatory response in cells compared to PPD. These results suggest that the new dyes can effectively color hair while avoiding the potential allergen and sensitization risks of more traditional dyes.

The authors acknowledge funding from the National University of Singapore.

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