j. Cosmet. Sci.! 56, 47-56 CTanuary/February 2005) A study of the photolightening mechanism of red hair with visible and ultraviolet light: Comparison with blond hair T. TAKAHASHI and K. NAKAMURA, Kao Corporation, Hair-Care Research Laboratories, 1-3, Bunka 2, Surnida-ku, Tokyo1 131-8501 Japan. Accepted for publication December 9, 2004. Synopsis 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 rel 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. It has been proven that chemically intact melanin in red hair is considerably more photolabile to UV light than VIS light. Also, it is much more easily decomposed by UV light than melanin granules in blond hair, although they are both similarly decomposed by VIS light. This indicates that pheomelanin is far more sensitive to UV light than eui;nelanin, while these two types of melanin are similarly sensitive to VIS light. This leads to the following hypothetical photolightening mechanism of red hair: When UV light is irradiated on red hair, the light is absorbed by hair protein and attenuated before it reaches the melanin granules. However, since pheomelanin is highly sensitive to UV light, even the attenuated UV light decomposes the pheomelanin to some extent. As a result, UV light lightens red hair without the need for subsequent washing, in contrast to blond hair, which consists of mainly eumelanin. INTRODUCTION It is well known that hair is subject to various influences from sunlight that affect its properties-for example, hair lightening, dryness, split hairs, etc. (3-7). Focusing on hair lightening, which is most noticeable, the photochange of blond hair in the early stages of irradiation was studied and reported previously (1). In that study, the inten­ sities of VIS and UV light were adjusted to represent their proportions in natural sunlight. It was proven that both light sources lighten blond hair, but through different mechanisms, which has led to the following hypothesis: VIS light attacks and decom­ poses melanin granules, which results in the lightening of blond hair. On the other hand, UV light preferentially attacks other hair tissues, causing hair fibers to become damaged 47

48 JOURNAL OF COSMETIC SCIENCE and loose. Washing the hair subsequent to UV light irradiation causes some melanin granules to effuse from the hair, which in turn leads to lightening. The ratio of eumelanin to pheomelanin has been quantified by some researchers. The results always agree that eumelanin is predominant in black or dark brown hair. In the case of blond or red hair, however, the results are sometimes inconsistent with each other. Some researchers reported that eumelanin prevails even in blond and red hair (2,8). Contrary to this, some researchers have reported pheomelanin to be predominant in red hair (9). Others mention that pheomelanin is predominant in blond hair (10). This discrepancy must come from not only the different measuring methods, but also from the hair samples used. In this study we have examined the photolightening behavior of red hair, whose melanin is predominantly pheomelanin. The blond hair used in our previous study (1) contained both eumelanin and pheomelanin. From this, the photo­ sensitivity of each type of melanin can be clarified by comparing photolightening behaviors between red hair and blond hair. There have been many studies on the photosensitivity of the above-mentioned two types of melanin, and two conflicting views exist. Some researchers have argued that phe­ omelanin is more easily degraded by UV light than eumelanin (11�13), often grounding their argument in the fact that redheads are highly susceptible to skin cancer. They consider that melanin in the skin of redheads is mainly pheomelanin, which is easily decomposed by UV light, and therefore cannot exhibit the role of protecting the skin against sunlight. On the contrary, other researchers offered a counterargument that pheomelanin was rather more photoresistant than eumelanin, based on the fact that the color of red hair does not change very much during summer (14). They noted that most of the other studies were undertaken using synthetic or isolated melanin, clarifying that it was more important to investigate the photosensitivity of melanin in natural condi­ tions. The controversy surrounding the photosensitivity of the two types of melanin has not been clarified for some decades. It is considered that synthesized melanin probably shows different properties from natural melanin, with isolated melanin granules denaturalized during the isolation process. On the other hand, irradiation of hair fibers can provide valuable information about the photochange of intact melanin in nature. However, the relationship between the degree of photodegradation of each type of melanin and the degree of color change of hair has not yet been established. Hence this can possibly lead to a misunderstanding if the color change in hair is related to the level of photodegradation of melanin. In our work, we examined chemically intact melanin granules of red hair using the same method of irradiating a cross section of hair that was applied to blond hair in the previous study (1). The photosensitivity was estimated by comparing the percentages of the disappeared melanin granules before and after irradiation. MATERIALS AND METHODS RED HAIR Chemically untreated Caucasian red hair was purchased from International Hair Im­ porters & Products Inc., New York. Tresses with a weight of 0.5 g and 8 cm in length