Light brown or black skin patches may be a sign of acanthosis nigricans. This treatable skin disorder isn't contagious or dangerous. However, it can be a sign of diabetes, so talk to your healthcare provider. Often, treating diabetes (or another underlying cause) causes the skin to clear up.
This skin disorder results in light-brown-to-black spots. It often happens to otherwise healthy people, but in some cases, it may be a sign of an underlying condition. The markings look like a spot or stain that you might think you can scrub off. But washing will not remove acanthosis nigricans (AN).
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The velvety markings that are characteristic of acanthosis nigricans (a-can-THO-sis NIH-grih-cans) can appear anywhere on the body. They most often show up on the skin folds of the neck, armpits and groin and under the breasts.
No, AN isn't contagious. You can't pass it to others or get it from other people.
The condition is not harmful, but it may be a sign of an underlying condition that requires treatment. If you notice unusual marks or skin shading, see your healthcare provider. Your provider or a dermatologist (skin specialist) will run some tests to determine what type of treatment you need.
Anyone can develop acanthosis nigricans, including otherwise healthy people. You may be at higher risk for getting this condition if you:
While AN doesn’t always mean you have diabetes or prediabetes, it can be a sign of diabetes. So talk to your healthcare provider if you notice signs of AN.
Prediabetes means you have early signs but haven’t yet developed diabetes. If you have prediabetes, your provider will talk to you about steps to take to reduce your risk of developing diabetes. And if you do have diabetes, you and your provider can discuss treatment options.
Acanthosis nigricans is a rare disease. Researchers don’t know how often it occurs in America. However, a study of adults with obesity found that of those who weighed double their ideal body weight, at least 50% showed signs of acanthosis nigricans.
AN can have many causes, including:
AN symptoms tend to develop slowly. If symptoms develop quickly, it may be a sign of cancer, though this is rare.
Signs of this skin condition include:
Symptoms tend to appear slowly, over months or even years. If these signs appear suddenly, see a dermatologist. It may be a sign of cancer.
Your healthcare provider will talk to you about your symptoms and medical history and perform a physical exam. Often, these steps are enough to diagnose AN. Other tests to diagnose AN include:
AN will not go away on its own, but you don’t always need medical treatment. If no underlying condition is causing AN, you can decide if you want to treat the dark patches.
People typically see good results after treatment. The skin clears, although the dark spots may not go away completely.
Treatment for AN depends on the cause. If AN is due to an underlying condition, such as diabetes or a hormonal condition, treating the condition will treat the skin problems.
Often, weight loss, exercise and a nutritious diet help reduce insulin levels, resulting in improved skin. The patches may even disappear completely.
Other treatments include:
Do not use skin care products to treat dark spots without consulting with a healthcare provider. These products may not work and may even irritate your skin, worsening the condition.
If the AN is related to elevated insulin, managing your weight and eating a healthy diet can help prevent or reduce the dark spots.
If obesity is causing AN, you can help prevent the condition through weight management. A diet that helps you keep your blood sugar (insulin) levels in check can also help prevent AN.
Other preventive steps include:
AN isn't dangerous or harmful. People can live normal, healthy lives with AN.
However, it’s important to manage conditions that may be causing AN, such as diabetes, obesity or hormonal conditions. And if the dark patches appear suddenly, see your healthcare provider immediately. The sudden appearance may be a sign of cancer.
Any time you notice changes in your skin, see your healthcare provider or a dermatologist. Small markings or changes may seem insignificant, but they may indicate a problem. Acanthosis nigricans can be a sign of prediabetes or diabetes. Talk to your provider so you can get the proper care.
A note from Cleveland Clinic
Acanthosis nigricans is a treatable skin condition that causes dark patches on your body. It is often (though not always) a sign of prediabetes or diabetes. Talk to your healthcare provider to find out if you have an underlying condition causing AN. A healthcare provider can help you get treatment to reduce the marks and help you feel and look your best.
Last reviewed by a Cleveland Clinic medical professional on 02/11/2021.
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