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Incidence of skin allergies is increasing today. Often provoked by environmental factors, to which skin is highly-sensitive, as an interface, they may also express internal processes that are inherent to an individual. We will focus here on three of them: eczema, atopic dermatitis and urticaria.

Melanodermic half-castes may develop a progressive and extensive hypomelanosis presenting as an original skin condition. The course of the disease is characteristic: it occurs mainly in females from 18 to 25 years of age with a progressive development of hypochromic and coalescent macules on the back and abdomen. This disease may regress spontaneously within 5 years and healing seems to be facilitated by UV exposure. Decreased epidermal melanin is the only histological feature. Ultrastructural examination has led to characterize this bizarre disease by a switch from stage IV single melanosomes negroid type to small type I-III aggregated melanosomes (caucasoid phenotype of melanogenesis). Although the pathogenesis of the disorder remains obscure, it may be stated that the variation in skin coloration in these patients is due to a variation in melanosome size and distribution. It is possible that this variation is due to a decrease in production of type IV melanosomes and that this apparent change of ultrastructural phenotype represent the consequence of a simple imbalance in melanosomes production favoring small I to III melanosomes. This disease is not restricted to a limited geographic group: it is present in melanodermic half-castes of different areas and therefore deserves to be known and recognized.