A study of the photolightening mechanism of red hair with visible and ultraviolet light: comparison with blond hair.

The photolightening behavior of red hair was investigated. Red hair was found to lighten to a similar extent by irradiation from both ultraviolet (UV) and visible (VIS) light. Under the same irradiating conditions, blond hair was lightened by VIS light but did not lighten by UV light until it was washed after irradiation (1). These different photolightening behaviors of red and blond hair are supposed to be due to differences in their melanin compositions. The dominant type of melanin in red hair is pheomelanin; while blond hair investigated in the previous work contained both eumelanin and pheomelanin, with mainly eumelanin (2). Consequently, in this investigation, the photolightening behaviors of red and blond hair were compared to clarify the differences in photosensitivity between the two types of melanin.