An uncommon, untreatable condition in which dark thickened patches of skin appear in the neck, armpits and groin and other skin folds. Acanthosis nigricans can occur in young people as a genetic disorder or as the result of Cushing’s syndrome or any other endocrine disorder. The condition also occurs in people with cancerous tumours of the lung and other organs. Pseudoacanthosis nigricans is a more widespread condition that is often seen in dark- complexioned people who are overweight or obese. When in this form the skin fold area in both darker and thicker than the surrounding skin and excessive sweating typically occurs in affected areas. Pseudoacanthosis nigricans can improve with weight loss.