Significance of hair‐dye base‐induced sensory irritation

Oxidation hair ‐ dyes, which are the principal hair ‐ dyes, sometimes induce painful sensory irritation of the scalp caused by the combination of highly reactive substances, such as hydrogen peroxide and alkali agents. Although many cases of severe facial and scalp dermatitis have been reported following the use of hair ‐ dyes, sensory irritation caused by contact of the hair ‐ dye with the skin has not been reported clearly. In this study, we used a self‐assessment questionnaire to measure the sensory irritation in various regions of the body caused by two model hair‐dye bases that contained different amounts of alkali agents without dyes. Moreover, the occipital region was found as an alternative region of the scalp to test for sensory irritation of the hair‐dye bases. We used this region to evaluate the relationship of sensitivity with skin properties, such as trans‐epidermal water loss (TEWL), stratum corneum water content, sebum amount, surface temperature, current perception threshold (CPT), catalase activities in tape‐stripped skin and sensory irritation score with the model hair‐dye bases. The hair‐dye sensitive group showed higher TEWL, a lower sebum amount, a lower surface temperature and higher catalase activity than the insensitive group, and was similar to that of damaged skin. These results suggest that sensory irritation caused by hair ‐ dye could occur easily on the damaged dry scalp, as that caused by skin cosmetics reported previously.