Acanthosis nigricans is the name given to thickened, darkened skin that occurs on the neck, under the arms, and in skin folds.
It may occur normally in some people as an inherited form called familial acanthosis nigricans. However, it may also be a sign of illness. For example, it may be caused by:
Sometimes acanthosis nigricans happens when you take certain medicines, such as nicotinic acid, diethylstilbestrol (DES), and steroids. Most often it is a sign that type 2 diabetes is developing.
You have a painless area of darkened, slightly raised skin. The area of skin may feel velvety. In rare cases it may itch.
The diagnosis is usually based on how your skin looks and where your skin is affected. If the diagnosis is uncertain, you may have a skin biopsy. When you have a biopsy, you are first given a numbing medicine. Then your provider removes a small piece of skin. The skin sample is sent to a lab. At the lab the sample is examined under a microscope.
There is no specific treatment for acanthosis nigricans. If it is caused by an illness, your provider will treat the illness. When it seems to be a side effect from a medicine, your provider may prescribe a different medicine.
If you have acanthosis nigricans, it is very important to get checked for type 2 diabetes and other possible causes. The skin changes often get better with the improved diet and exercise that treats or helps prevent diabetes.
If you have the inherited form (familial acanthosis nigricans), creams put on the skin may be helpful.
Acanthosis nigricans will last as long as the underlying cause is present. If you have insulin resistance or diabetes, the rash may improve or go away with weight loss or other treatment of the diabetes. If the acanthosis nigricans is due to cancer, then your skin may become more normal after the tumor is removed.
The most important thing you can do is to talk to your healthcare provider and work with him or her to determine the underlying cause.