INVITED ARTICLE Diversity of human hair pigmentation as studied by chemical analysis of eumelanin and pheomelanin S. Ito,* K. Wakamatsu Department of Chemistry, Fujita Health University School of Health Sciences, Toyoake, Aichi, Japan *Correspondence: S. Ito. E-mail: sito@fujita-hu.ac.jp Abstract Hair colour is one of the most conspicuous phenotypes in humans, ranging from black, brown, blond to red. This diversity arises mostly from the quantity and ratio of the black-dark brown eumelanin and the reddish-brown pheomelanin. To study the chemical basis underlying the diversity of hair colour, we have developed several chemical methods to quantify those two pigments. Alkaline H 2 O 2 oxidation affords pyrrole-2,3,5-tricarboxylic acid (PTCA) as a eumelanin marker and thiazole-2,4,5-tricarboxylic acid (TTCA) as a pheomelanin marker. Pheomelanin can also be analysed as 4-amino-3-hydroxyphenylalanine (4-AHP) after hydroiodic acid hydrolysis. Using those methods, we evaluated the contents of eumelanin and pheomelanin (the ‘chemical’ phenotype) in human hairs of black, dark brown, brown, light brown, blond and red colour (the ‘visual’ phenotype). Eumelanin contents decrease in that order, with a trace but constant level of pheomelanin, except for red hair which contains about equal levels of pheomelanin and eumelanin. Thus, the chemical phenotype correlates well with the visual phenotype. The genotype of melanocortin-1 receptor (MC1R), a gene regulating the red hair phenotype, is predictive of hair melanin expressed as the log value of eumelanin to pheomelanin ratio, with a dosage effect evident. Hair melanin contents were also analysed in patients with various hypopigmentary disorders including Hermansky–Pudlak syndrome, Menkes disease, proopiomelanocortin deficiency, cystinosis, malnutrition and trace metal deficiency. The chemical phenotype helped evaluate the precise effects of each disease on pigmentation. In studies of human hair, the chemical phenotype will find more and more application as an objective measure of pigmentation. Received: 14 June 2011; Accepted: 12 July 2011 Conflict of interest None declared. Funding sources This work was supported, in part, by a grant from the Japan Society for the Promotion of Science (JSPS) (No. 20591357). Key points d Diversity of hair colour arises mostly from the quantity and ratio of the black-dark brown eumelanin and the reddish- brown pheomelanin. d ‘Visual’ inspection of hair colour is not only subjective but also qualitative. Therefore, we developed ‘chemical’ methods to analyse those two pigments objectively and quantitatively. d Eumelanin can be analysed as a specific degradation product, pyrrole-2,3,5-tricarboxylic acid after alkaline H 2 O 2 oxidation. d Pheomelanin can be analysed as specific degradation prod- ucts, thiazole-2,4,5-tricarboxylic acid (TTCA) after alkaline H 2 O 2 oxidation or 4-amino-3-hydroxyphenylalanine (4-AHP) after hydroiodic acid hydrolysis. d The ‘chemical’ phenotype of human hairs correlates well with the ‘visual’ phenotype. Thus, black, dark brown, brown, light brown and blond hairs are eumelanic with melanin content in this order, while only red hairs contain equal amounts of eumelanin and pheomelanin. d Pathologically hypopigmented hairs can also be analysed with those methods to obtain a deeper understanding of the biochemical basis of the disease. d The alkaline H 2 O 2 oxidation method is simple and repro- ducible, and thus is suitable for broader use among research- ers who do not have special expertise in analytical chemistry. Introduction Hair pigmentation is one of the most conspicuous phenotypes of humans. It ranges in colour from black, dark brown, brown, light brown and blond to red with subtle hues in each category. Hair colour has an enormous cosmetic and social impact as exemplified ª 2011 The Authors JEADV 2011, 25, 1369–1380 Journal of the European Academy of Dermatology and Venereology ª 2011 European Academy of Dermatology and Venereology DOI: 10.1111/j.1468-3083.2011.04278.x JEADV