Skin changes are the only signs of acanthosis nigricans. You'll notice dark, thickened, velvety skin in body folds and creases — typically in your armpits, groin and back of the neck. The skin changes usually appear slowly. The affected skin may also have an odor or itch.

Acanthosis nigricans has been associated with:

• Insulin resistance. Most people who have acanthosis nigricans have also become resistant to insulin. Insulin is a hormone secreted by the pancreas that allows your body to process sugar. Insulin resistance is what eventually causes type 2 diabetes.
• Hormonal disorders. Acanthosis nigricans often occurs in people who have disorders such as ovarian cysts, underactive thyroids or problems with the adrenal glands.
• Certain drugs and supplements. High-dose niacin, birth control pills, prednisone and other corticosteroids may cause acanthosis nigricans.
• Cancer. Acanthosis nigricans also sometimes occurs with lymphoma or when a cancerous tumor begins growing in an internal organ, such as the stomach, colon or liver.

Acanthosis nigricans risk factors include:

• Obesity. The heavier you are, the higher your risk of acanthosis nigricans.
• Race. Studies show that in the United States, acanthosis nigricans is more common among Native Americans.
• Family history. Some types of acanthosis nigricans appear to be hereditary.

People who have acanthosis nigricans are much more likely to develop type 2 diabetes.