Acanthosis Nigricans

What acanthosis nigricans looks like

The patches are:

• brown to gray-black, darker than the surrounding skin
• thickened, with a velvety or leathery texture you can feel
• usually symmetrical, on both sides of the body
• often accompanied by small skin tags in the same area
• sometimes mildly itchy or with a slight odor

Common places are the back and sides of the neck, armpits, groin, inner thighs, under the breasts, elbows, knees and knuckles. People often mistake it for dirt that will not wash off.

What causes it

Insulin resistance (most cases)

When the body becomes resistant to insulin, the pancreas produces more of it. High insulin levels stimulate skin cells (keratinocytes) and pigment cells to multiply, especially in skin folds, through insulin-like growth factor receptors. That is why acanthosis nigricans is so closely linked to:

• obesity
• prediabetes and type 2 diabetes
• polycystic ovary syndrome
• metabolic syndrome

It is more common in people with darker skin, including people of African, Hispanic and Native American descent. In children and teenagers, it is a strong signal to test for prediabetes and type 2 diabetes.

Hormonal conditions

• Cushing syndrome (excess cortisol)
• hypothyroidism
• acromegaly (excess growth hormone)
• rare severe insulin resistance syndromes

Medicines

Systemic steroids, high-dose niacin, oral contraceptives, some protease inhibitors and insulin injections (at the injection site) can cause it.

Inherited forms

Familial acanthosis nigricans appears in childhood or at puberty in otherwise healthy people and runs in families.

Malignant acanthosis nigricans

Rarely, acanthosis nigricans is caused by a substance released by a tumor, most often a stomach adenocarcinoma. Warning features are sudden onset in an adult who is not overweight, rapid spread, involvement of the mouth, lips or palms, itching, and weight loss. This needs prompt investigation.

Diagnosis

A doctor can usually diagnose acanthosis nigricans by looking at it. The important step is finding the cause:

• blood tests: fasting glucose and HbA1c, sometimes fasting insulin and lipids
• hormone tests if PCOS, Cushing syndrome or thyroid disease is suspected
• review of medicines
• screening for cancer (endoscopy and imaging) only when features suggest the malignant form
• skin biopsy, rarely, if the appearance is unusual

Treatment

Treat the cause

• Weight loss and exercise: improve insulin sensitivity and often fade the patches over months. Even a 5 to 10 percent weight loss helps.
• Diabetes and prediabetes treatment: metformin and other medicines that improve insulin resistance can help.
• PCOS management and treatment of other hormonal problems.
• Stopping or changing a causative medicine, where possible.
• Treating an underlying cancer usually improves malignant acanthosis nigricans.

Treatments for the skin

These improve appearance but do not treat the cause:

• topical retinoids (tretinoin)
• creams with urea, lactic acid or salicylic acid to soften thickened skin
• topical vitamin D analogs (calcipotriol)
• chemical peels and laser treatment, used by dermatologists
• antibacterial soap if there is odor

Scrubbing does not remove the patches and can irritate the skin.

Outlook

Acanthosis nigricans is not contagious or dangerous by itself. Patches caused by insulin resistance often lighten significantly when weight and blood sugar improve, though it can take many months. Its real value is as an early warning: acting on it can prevent or delay type 2 diabetes and its complications.

Frequently asked questions

What causes acanthosis nigricans?

Most cases are caused by insulin resistance, usually linked to obesity, prediabetes, type 2 diabetes or PCOS. Other causes include hormone disorders, some medicines such as steroids and niacin, inherited forms, and rarely an internal cancer, especially stomach cancer.

Does acanthosis nigricans mean I have diabetes?

Not necessarily, but it often means insulin resistance, which raises your risk of type 2 diabetes. Many people with it have prediabetes or diabetes. A simple blood test for glucose or HbA1c can check.

Will acanthosis nigricans go away?

It often fades when the cause is treated. Losing weight, exercising and improving blood sugar can lighten patches over months. Creams such as retinoids can help further. Patches from inherited forms may persist.

Is acanthosis nigricans dangerous?

The skin changes themselves are harmless. Their importance lies in what they signal: usually insulin resistance and diabetes risk, and very rarely an internal cancer. Sudden, rapidly spreading patches in an adult who is not overweight need prompt evaluation.