Tinea nigra

Tinea nigra, also known as superficial phaeohyphomycosis and Tinea nigra palmaris et plantaris, is a superficial fungal infection, a type of phaeohyphomycosis rather than a tinea, that causes usually a single 1–5 cm dark brown-black, non-scaly, flat, painless patch on the palms of the hands and the soles of the feet of healthy people. There may be multiple spots. The macules occasionally extend to the fingers, toes, and nails, and may be reported on the chest, neck, or genital area.: 311  Tinea nigra infections can present with multiple macules that can be mottled or velvety in appearance, and may be oval or irregular in shape. The macules can be anywhere from a few mm to several cm in size.

Most cases are caused by Hortaea werneckii, a pigmented fungus, which is a dark yeast found in sewage, soil, rotting vegetation and wood and in places with a high salt content such as moldy salted fish and on beaches, where contact with sand may result in transmission. Infection is by direct contact and the fungus enters and remains in the outer dead layer of skin with little or no skin inflammation. The infection does not invade deeper tissues.

Diagnosis is by visualisation, dermoscopy, and microscopy and culture of skin scrapings. Differential diagnosis includes Addison's disease, syphilis, pinta, yaws, melanoma, lentigines, lichen planus of the palms, and junctional melanocytes nevus. Treatment is with topical Whitfield's ointment or salicylic acid ointment. Topical antifungals or oral itraconazole are other options. Scraping the lesion can be curative. Prevention is by general hygiene measures.

It is uncommon. It generally occurs in tropical and subtropical countries of Central and South America, the Caribbean, Europe, South East Asia, Australia and the Far East. The disease was first described by Alexandre Cerqueira from Brazil in 1891. No cases in animals have been reported.

Source: Wikipedia