Acanthosis nigricans (AN) is a skin condition marked by dark patches, especially in the folds of the skin. It is most common in obese people and in those who have or may develop type 2 diabetes (condition characterized by the body’s inability to use the hormone insulin effectively).

There are two major types of AN:

• Benign acanthosis nigricans. This type can be divided into three categories:
  
  
• Endocrine. Most commonly affiliated with type 2 diabetes or insulin resistance.
  
  
• Drug induced. Often results from the use of oral steroids, birth control pills or nicotinic acid (a cholesterol lowering agent).
  
  
• Idiopathic. The cause is unknown.

• Malignant acanthosis nigricans. This type is rare and associated with cancerous internal tumors (abnormal growths).

Scientists are not certain what causes AN. It appears to be due to overstimulation of skin cells of the epidermis. AN can affect people of all ages and both genders. People with darker skin are more susceptible to AN than people with lighter skin.

AN does not pose a health threat to patients and is primarily a cosmetic problem of the epidermis. Certain people may develop itchiness (pruritus) associated with the skin plaques. However, the underlying condition that causes AN may be relatively harmless (e.g., use of certain medications) or potentially life-threatening (e.g., aggressive cancers), and may require medical treatment.

A physical examination and medical history are the primary methods of diagnosing AN. In some cases, blood tests or biopsies may also be helpful in determining a diagnosis.

Losing weight and making other lifestyle changes to reduce the levels of insulin in the blood may improve most cases of AN. In other cases, stopping the use of the medication that triggered the condition or treating an underlying tumor may be the key to reversing AN.