Acanthosis nigricans is a skin condition that causes the skin to become darker and thicker. It most often appears in the skin folds around the neck, groin, and armpits. Other symptoms include itching and an odor.
Acanthosis nigricans has links with obesity and diabetes, and treatment involves addressing the underlying disorder. In rare cases, a malignant form of acanthosis nigricans can occur in people who have certain cancers.
In this article, we discuss the causes and symptoms of acanthosis nigricans, and we list some of the available treatment options.
The main symptoms of acanthosis nigricans are the following:
- Hyperpigmentation: This is when certain areas of skin become darker, or more pigmented, and may turn greyish, black, or brown.
- Hyperkeratosis: This is when areas of skin become thicker and may take on a velvet-like appearance. Eventually, skin lines may become deeper and more noticeable, and wart-like growths can appear.
Acanthosis nigricans can also cause the following additional skin symptoms:
- excessive roughness
- an unusual odor
Malignant acanthosis nigricans may cause more severe and extensive skin changes than the benign (noncancerous) form.
Some people experience these skin changes on one side of their body only. This is known as unilateral acanthosis nigricans.
Changes to the skin typically develop slowly. Occasionally, they can be present from birth, but they usually appear in childhood or adulthood. They can occur anywhere, but commonly affect the:
- back and sides of the neck
Less commonly, acanthosis nigricans develops on the:
- back of the knees
- front of the elbows
- palms of the hands
- soles of the feet
- under the breasts
Acanthosis nigricans is not a disease in itself. Rather, it is a symptom of an underlying disorder. The skin changes take place when skin cells start to reproduce too quickly.
The following factors can cause acanthosis nigricans:
- Insulin resistance: Acanthosis nigricans commonly affects people with obesity and insulin resistance, which is a situation where the body cannot use insulin effectively. Insulin resistance eventually leads to type 2 diabetes.
- Hormonal changes: People with hormonal disorders, such as Addison's disease, polycystic ovary syndrome (PCOS), or hypothyroidism may develop acanthosis nigricans.
- Genetics: Hereditary acanthosis nigricans may be present from birth, but most people develop it during childhood or later in life.
- Medication use: Taking medications, such as birth control pills, corticosteroids, or high doses of niacin, can lead to the onset of acanthosis nigricans. Some bodybuilding supplements may also cause this skin disorder.
- Cancer: In rare cases, malignant acanthosis nigricans can occur in people with certain types of stomach cancer, including gastric adenocarcinoma, as well as other carcinomas and lymphomas.
Risk factors for acanthosis nigricans include:
- Obesity. People who are overweight are more likely to be resistant to insulin or have diabetes. Research suggests that up to 74 percent of people who are obese may have this condition. Obesity-associated acanthosis nigricans may be higher in females.
- Ethnicity. According to the American Academy of Dermatology, acanthosis nigricans is more common in people who are of African, Caribbean, Hispanic, or Native American descent.
- Genetics. People with family members that have acanthosis nigricans are at a higher risk of developing the condition.
- Having a hormonal disorder. Those with conditions that affect their hormones are more likely to get acanthosis nigricans than others.
- Taking certain medications or supplements. Some medicines, including hormonal birth control and steroids, increase the risk of developing acanthosis nigricans.
Typically, doctors begin by treating the underlying disorder. Once this is under control, the skin changes often go away.
Treatments vary depending on the underlying issue, and include:
People who have acanthosis nigricans as a result of obesity or insulin resistance may find that their skin improves once they lose weight.
Weight loss may improve skin texture, but the discoloration can remain.
For people with hormonal disorders, acanthosis nigricans may resolve if they get their condition under control using medications, lifestyle changes, and other treatments.
People with type 2 diabetes may require medications, regular monitoring of blood sugar levels, and dietary and lifestyle modifications. Once insulin levels become stable, acanthosis nigricans symptoms may resolve.
Avoiding certain medications
If specific drugs or supplements are causing acanthosis nigricans, then a doctor may recommend avoiding them or switching to an alternative. In most cases, the skin will go back to normal after discontinuing the medication.
To reduce the appearance or odor of acanthosis nigricans, some people try cosmetic treatments, such as:
- prescription creams to lighten the skin or to soften thick and rough patches
- laser therapy to reverse skin thickening or lighten the skin
- antibacterial soaps
- topical antibiotics
- oral medications
Cosmetic treatments do not address the underlying cause of acanthosis nigricans, although they can improve the skin's appearance until other treatments take effect.
People who notice skin darkening, thickening, or other skin changes should make an appointment to see their doctor. The changes are often harmless, but they can suggest a medical condition that requires treatment.
A doctor can often diagnose acanthosis nigricans by merely looking at the skin. However, they may need to perform additional tests to determine its underlying cause. Diagnostic tests include:
- a biopsy, where a doctor removes a small skin sample to examine under a microscope
- blood tests
Acanthosis nigricans associated with cancer, known as malignant acanthosis nigricans, is rare.
Malignant acanthosis nigricans is more common older adults, where it affects both genders equally.
When it does occur, it most commonly affects people with abdominal cancers such as:
- gastric cancer
- esophageal cancer
- pancreatic cancer
The symptoms of malignant acanthosis nigricans are similar to those of the benign form, but they may be more severe and widespread. They can also affect the mouth and the area around the eyes.
Acanthosis nigricans has links to insulin resistance and is common in people with diabetes or at risk of diabetes.
Children who have acanthosis nigricans are at higher risk of type 2 diabetes later in life.
Acanthosis nigricans is a relatively common skin disorder characterized by patches of dark, thick, and velvety skin that has associations with being overweight and diabetes.
Acanthosis nigricans typically signals an underlying condition, such as diabetes or a hormonal disorder. Rarely, it can suggest the presence of an abdominal or gynecological cancer.
People who notice skin changes should see their doctor for diagnosis and treatment. Acanthosis nigricans usually clears up once the underlying disorder is under control. Until then, cosmetic treatments can improve skin appearance and reduce odors.