The color of the human skin and hair is largely dependent on the amount of melanin1 contained therein. The brownish tint of the skin of dark complexioned and of some pathologically pigmented persons is attributable chiefly to an increased quantity of epidermal (ectodermal) melanin, and in a much less degree to an increase in dermal (mesodermal) melanin. In some cases of tar and arsenical hyperpigmentations and in cases called by Bloch "incontinentia pigmenti," the dermal pigment (chromatophores) plays the greater rôle in the process, and the color tends toward a slate grayish hue, if there is not too much overlying epidermal pigment. The blue which occurs in some abnormal conditions, such as Mongolian spot and blue nevus (Jadassohn), is due to the presence of dermal (mesodermal) melanoblasts, which are much more numerous and important in animals, for example, in the apes, to which is attributable the blue of their
BECKER SW. MELANIN PIGMENTATIONA SYSTEMATIC STUDY OF THE PIGMENT OF THE HUMAN SKIN AND UPPER MUCOUS MEMBRANES, WITH SPECIAL CONSIDERATION OF PIGMENTED DENDRITIC CELLS. Arch Derm Syphilol. 1927;16(3):259–290. doi:10.1001/archderm.1927.02380030002001
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