Plant-derived dyes have been used on hair for centuries and consumers are becoming more interested in plant-based options as an alternative to chemical dyes. One of the reasons for consumer interest is the perception that plant-based hair dye may be less irritating and toxic than synthetic dye. However, plant-based dyes may still cause skin and eye irritation and they may not be as effective at saturating hair with lasting color.
A recent study sought to provide a framework to assess both dyeing efficiency and irritation potentials of formulas that combined plant colorants and hydrogel hair dyes. In the study, the dyes were directly applied to unbleached gray human hairs and the eye/skin irritancy of the formulations was evaluated by combining several in vitro methods.
The results showed that all four naturally-derived dyes had good dyeing performance on human hairs in preferred shades. The four examined plant extracts, when formulated in hydrogels, may prove a low-irritating alternative to the synthetic hair dyes. The dyes did not cause skin irritation, but some did cause eye irritation, though at similar or lesser levels than synthetic dyes.
The authors note that although their study suggests that the investigated formulas of plant hair dyes seem to be relatively innocuous to consumers, further in vivo research is necessary to better compare natural dyes to synthetic dye ingredients.