In acanthosis nigricans, the skin becomes thick and velvety. It may appear gray, brown, or black, and often appears in skin folds. It is often a sign of an underlying condition, such as insulin resistance.

Acanthosis nigricans often develops around the neck, groin, and armpits. There may also be itchiness.

The condition is more likely to occur if a person has obesity or diabetes or uses certain medications. In some cases, it can occur due to cancer. However, usually, acanthosis nigricans itself is not harmful.

In this article, we discuss treatment options for acanthosis nigricans, as well as the symptoms, causes, and links with other conditions.

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Acanthosis nigricans occurs when certain skin cells reproduce too quickly, leading to hyperpigmentation and hyperkeratosis.

Hyperpigmentation is when pigment increases in certain areas of skin, making them darker. Hyperkeratosis is when the outer layer of skin becomes thicker due to the body producing extra keratin.

Potential causes include:

Insulin resistance

Acanthosis nigricans commonly affects people with obesity and insulin resistance, where the body cannot use insulin effectively. Insulin resistance eventually leads to type 2 diabetes.

Hormone conditions

People with hormonal imbalances, such as Addison’s disease, polycystic ovary syndrome (PCOS), or hypothyroidism may develop acanthosis nigricans.

Genetics

Hereditary acanthosis nigricans may be present from birth, or may develop during childhood.

Very rarely, people can inherit unilateral acanthosis nigricans, also known as nevoid acanthosis nigricans, from their parents. This causes symptoms on one side of the body.

Medication use

Drugs that may trigger acanthosis nigricans include:

Some autoimmune conditions

People with lupus, Sjogren’s syndrome, scleroderma, or Hashimoto’s thyroiditis may develop acanthosis nigricans.

Cancer

Rarely, acanthosis nigricans occurs alongside some types of cancer, such as:

When this happens, it is known as malignant acanthosis nigricans syndrome. Skin changes may appear before, during, or after the cancer develops.

Other risk factors

According to the American Academy of Dermatology, people of Native American, Caribbean, African, or Hispanic descent are more likely to develop acanthosis nigricans.

However, the reasons for this are currently unclear. A 2024 review states that more research is necessary.

The main symptoms of acanthosis nigricans are hyperpigmentation and hyperkeratosis. A person may notice changes in the color and texture of their skin. The color may become gray, black, or brown. The texture may become velvety.

In some cases, these areas may progress and develop plaques, or raised and hardened areas of skin. A person may also experience:

These changes usually take months or years to appear. Occasionally, they are present from birth. If they develop rapidly, this could be a sign of cancer.

Acanthosis nigricans can occur anywhere on the body, but commonly affects the:

  • armpits
  • neck folds, especially on the back and sides of the neck
  • genitals
  • groin
  • under the breasts
  • anus
  • knees
  • knuckles
  • elbows
  • belly button
  • palms of the hands
  • soles of the feet

Less commonly, acanthosis nigricans may appear on the:

  • nipples
  • mucous membranes, including those in the mouth, nose, and throat
  • part of the eye and eyelids

The following images show how acanthosis nigricans can appear on the skin.

Acanthosis nigricans does not have a specific cure, but treating the underlying cause can allow it to fade over time. Some topical treatments may also reduce its appearance.

Treating the symptoms

For most people, treatment for acanthosis nigricans is cosmetic, meaning it mostly focuses on reducing the appearance of the lesions.

This is especially true if there is no treatable underlying cause, such as when a person has the condition due to genetics.

A dermatologist may suggest:

  • keratolytics, which dissolve and remove excess skin cells
  • retinoids
  • hydroquinone, which may lighten the skin
  • podophyllin, which doctors also use to treat warts
  • vitamin D analogs, such as calcipotriol (calcipotriene), which reduce the production of keratin

Cosmetic procedures that may help include:

  • dermabrasion, which is a type of exfoliation
  • alexandrite laser, which is a type of red light laser with a specific wavelength
  • chemical peels

People should talk with their doctor before using any of these products, as they are not suitable for everyone. Some can also increase skin sensitivity to sunlight. Always wear sunscreen when going outside.

Treatment for underlying conditions

Treatment for the cause of acanthosis nigricans may involve:

  • Weight management: Maintaining a moderate weight may help improve insulin sensitivity in those with insulin resistance. In turn, skin symptoms may improve.
  • Managing blood sugar: People with type 2 diabetes may need medications, monitoring of blood sugar levels, and some dietary and lifestyle adjustments. Once blood sugar levels become stable, acanthosis nigricans symptoms may resolve.
  • Balancing hormones: Medication and lifestyle adjustments may help reduce symptoms of acanthosis nigricans in those with hormonal conditions such as PCOS.
  • Medication changes: People who have concerns that their medications could be causing the condition can speak with their doctor about alternatives.

Treatment for malignant acanthosis nigricans includes surgical removal of a cancerous tumor. Other treatments a person may need include chemotherapy and radiation therapy.

If acanthosis nigricans is a result of genetics, the patches may grow slowly then stop or reduce in size without treatment.

However, if an underlying condition is the cause, the changes will remain. Treating the cause may improve the symptoms.

Insulin resistance, which is a feature of type 2 diabetes, has links to acanthosis nigricans. As a result, people with type 2 diabetes may develop this skin symptom.

When people have insulin resistance, their bodies can no longer process glucose effectively. The body produces more insulin in an attempt to manage this, resulting in high levels of both insulin and glucose in the body. These high levels of insulin can cause skin cells to reproduce more rapidly.

Anyone who notices these skin changes should seek medical advice, as they may need treatment to prevent or manage type 2 diabetes.

Acanthosis nigricans often occurs in those with PCOS. This condition causes an imbalance in reproductive hormones, affecting both the reproductive system and a person’s metabolism.

People with PCOS can develop insulin resistance, and may have difficulty maintaining a moderate weight. Either factor may increase the likelihood of getting acanthosis nigricans.

People who notice skin darkening, thickening, or other skin changes should make an appointment to see their doctor. The changes are often harmless. However, they can suggest a medical condition that needs treatment.

Anyone who notices a mole or mark on the skin that is quickly growing, changing color, or appearing in multiple places should speak with a doctor as soon as they can.

Acanthosis nigricans involves skin changes leading to patches of dark, thick, and velvety skin. These may appear on the neck, underarms, skin folds, and other parts of the body.

Obesity and insulin resistance are risk factors. PCOS, medication use, cancer, and some other conditions can also cause it.

People who notice skin changes should see their doctor, as they may need treatment for an underlying disorder. Treating an underlying condition may improve skin symptoms. Some topical and cosmetic treatments may also help.