Acanthosis nigricans (AN) is characterized by dark, gray-brown to black plaques. These skin changes usually appear very gradually, sometimes over a period of months or years. Often the discolored areas thicken and become raised plaques. Small noncancerous outgrowths called acrochordons, or skin tags, may develop. Sometimes, itching (pruritus) is present.

AN occurs most often in obese people in the folds of skin, such as the neck, inner elbows, armpits, abdomen and groin. Sometimes it is seen over the joints or on the scalp, eyelids, mouth, palms of the hands or soles of the feet. Patients may complain that their skin looks dirty and cannot be scrubbed clean.

AN is sometimes confused with psoriasis. However, the plaques of AN are not red and inflamed like those caused by psoriasis.