Acanthosis Nigricans

February 7, 2017

Acanthosis nigricans (AN) is a skin disorder characterised by darkening (hyperpigmentation) and thickening (hyperkeratosis) of the skin, occurring mainly in the folds of the skin in the armpit (axilla), groin and back of the neck. Acanthosis nigricans is not a skin disease per se but a cutaneous sign of an underlying condition or disease.

Acanthosis nigricans is not contagious. It is not harmful. It is a warning sign of a health problem that requires medical attention. For this reason, it is important to see a dermatologist if you notice an area of darker, thicker skin.

Acanthosis nigricans is seen in both men and women. It is most common in those who are overweight, have darker skin, and have diabetes or pre-diabetic conditions.

The frequency of acanthosis nigricans varies between ethnic groups, and appears in –

  • 1 percent of Caucasians
  • 6 percent of Latinos
  • 13 percent of African Americans
  • 34 percent of Native Americans

All ethnic groups are equally at risk of acanthosis nigricans when body mass index (BMI) is well above normal. It can occur with endocrine diseases such as Cushing disease and diabetes mellitus, from tumors of the pituitary gland, underlying malignancies, certain drugs, and as a genetic disorder. It is most common in people who have insulin resistance those whose body is not responding correctly to the insulin that they make in their pancreas.

There are two important types of acanthosis – Benign and Malignant. Although classically described as a sign of internal malignancy, this is very rare. Benign types, sometimes described as ‘pseudoacanthosis nigricans’ are much more common.


People get this skin condition for many reasons. Obesity is the most common cause. Studies show that when obese children and adults who have AN lose a significant amount of weight, they often see their skin clear.

People who are completely healthy also get AN. These people tend to have others in their family with this skin condition.

Eating too much of the wrong foods, especially starches and sugars, can cause insulin resistance. This will result in elevated insulin levels. Most patients with acanthosis nigricans have a higher insulin level than those of the same weight without acanthosis nigricans. Elevated levels of insulin in most cases probably cause acanthosis nigricans. The elevated insulin levels in the body activates insulin receptors in the skin, forcing it to grow abnormally. Reducing the circulating insulin by dieting or medication can lead to improvement of the skin problem.

Obesity – Acanthosis nigricans is usually the result of obesity. This is known as obesity-associated acanthosis nigricans. It occurs because obesity can cause insulin resistance (when the body is unable to properly use the hormone insulin), which may lead to high levels of insulin in the blood, affecting the skin cells. Insulin resistance can also cause type 2 diabetes, so acanthosis nigricans can be an early sign that you have diabetes or are at risk of developing the condition.

Other Health Condition

  • Pre-diabetes or diabetes – If you have pre-diabetes, making some lifestyle changes can help prevent diabetes. If you have diabetes, it is important to find out so that you can treat it.
  • A reaction to a medicine – Birth control pills, strong corticosteroids like prednisone, and niacin can cause AN.
  • Hormonal disease – This skin condition can be a sign of polycystic ovarian syndrome (PCOS), thyroid disease, or a problem with the adrenal glands.
  • Cancer – When AN develops quickly, it can be a sign of a cancer, especially a cancer in the stomach, colon, or liver.

Genes – In rare cases, acanthosis nigricans can be caused by a faulty gene inherited directly from your parents. This is known as familial or benign genetic acanthosis nigricans.

This type is usually passed on in an autosomal dominant pattern, which means it can be passed on if only one of your parents carries the faulty gene.

Cancer – If the dark skin patches come on suddenly and spread quickly, it may be a sign you have cancer (usually stomach cancer). This is known as malignant acanthosis nigricans. This is a rare condition that tends to affect middle-aged or elderly people, regardless of their weight or ethnic background.


This skin condition causes some easily recognized signs and symptoms. You may notice:

  • Brown or black discoloration on your skin.
  • Affected skin may feel velvety and thicker than the surrounding skin.
  • Skin tags may form on the darkened skin.
  • Skin can itch.
  • Skin can have a bad odor.

A velvety, dark patch of skin can form on most areas on the body, including the:

  • Armpits.
  • Back of the neck.
  • Groin area (especially in skin folds and creases).
  • Elbows.
  • Knees.
  • Knuckles.
  • Belly button.
  • Woman’s breasts (beneath).
  • Face.
  • Female genitalia.

Less often, a patch can form on the lips, mouth, eyelids, palms of the hands, bottoms of the feet, and nipples.

Acanthosis nigricans (AN) tends to appear slowly, taking months or years to form. If it appears suddenly, you should immediately make an appointment to see a dermatologist. When AN appears suddenly, it can be a warning sign of cancer.


The most effective treatment is obtained through weight loss and exercise. Eating a healthy diet can help reduce circulating insulin and can lead to improvement, and sometimes resolution, of the skin problem.

Other treatments to improve skin appearance, including Retin-A, urea, alpha hydroxy acids, and salicylic acid prescriptions, may be helpful in some people. Dermabrasion or laser therapy may help to reduce the bulky portion of the affected skin.

Acanthosis nigricans caused by medicine may go away once the medication is stopped.