What is acanthosis nigricans?

Acanthosis nigricans is a skin disorder that results in velvety, light-brown-to-black markings that can occur in any location but mainly are found in the skin folds of the neck, armpits, groin, and under the breasts.

What causes acanthosis nigricans?

Acanthosis nigricans can affect otherwise healthy people, or it can be associated with certain medical conditions. Sometimes acanthosis nigricans is congenital (something a person is born with). It is more likely to be seen in people with darker skin. The most common type is found in conditions that are associated with an elevated insulin blood level, such as in diabetes and obesity. There are many other possible causes of acanthosis nigricans, including:

  • Addison disease, a condition caused by a deficiency of hormones from the adrenal gland.
  • Disorders of the pituitary gland within the brain.
  • Growth hormone therapy.
  • Hypothyroidism (low levels of thyroid hormone caused by decreased activity of the thyroid gland).
  • Oral contraceptives.
  • Some cholesterol medications, including nicotinic acid.

Most people with acanthosis nigricans have an insulin level that is higher than that of people of the same weight who don't have acanthosis nigricans. Eating too much of the wrong foods, especially starches and sugars, and being overweight can raise insulin levels.

Rarely, people with certain types of cancer can also develop severe cases of acanthosis nigricans.