Scientists are not certain what causes acanthosis nigricans (AN). It appears to be due to overstimulation of the epidermal skin cells. AN is often the result of obesity caused by insulin resistance. This is a condition in which the body makes insulin but no longer uses it properly. Insulin is the hormone that regulates blood sugar (glucose) levels. Insulin resistance causes a buildup of insulin in the blood (hyperinsulinemia).

The excess insulin may activate insulin receptors in the skin and cause the abnormal growth. Excess insulin can indicate or lead to several serious health conditions. It is also a major factor in the development of diabetes (condition characterized by the body’s inability to produce or use the hormone insulin effectively).

Other factors are also believed to cause some cases of AN by overexciting skin cells. These include:

• Endocrine disorders. Conditions that affect the endocrine system, a group of glands that use hormones to help control reproduction, metabolism, growth and development. Examples of these disorders include polycystic ovary syndrome and Cushing’s syndrome.
  
  
• Heredity. AN can be inherited as an autosomal recessive or dominant trait, meaning that just one parent has to have an abnormal gene in order for a child to inherit the disease.
  
  
• Cancer. The skin cell overgrowth is stimulated by a tumor (abnormal growth) or as a response to a tumor. Examples of such cancers include lymphoma and cancers of the gastrointestinal or genitourinary tracts. It tends to affect people who are middle-aged, even if they are not obese.
  
  
• Medications. Certain medications can trigger AN. These include human growth hormone, nicotinic acid (a drug to lower high cholesterol levels), birth control pills, steroids, and pituitary and other drugs for endocrine system conditions.

AN affects people of all ages and genders. People with darker skin are more susceptible to AN than people with light-colored skin.