Acanthosis nigricans is a rare, untreatable condition in which thickened dark patches of skin appear in the groin, armpits, neck, and other skin folds.

Acanthosis nigricans may occur in young people as a genetic disorder or as the result of an endocrine disorder such as Cushing’s syndrome. The condition also occurs in people with carcinomas (cancerous tumours) of the lung and other organs.

Pseudoacanthosis nigricans is a much more common condition that is usually seen in dark-complexioned people who are overweight. In this form, the skin in fold areas is both thicker and darker than the surrounding skin, and excessive sweating usually occurs in affected areas. Pseudoacanthosis nigricans may improve with weight loss.