Acanthosis nigricans is the name for dry, dark patches of skin that usually appear in the armpits, neck or groin. It could be a sign of an underlying condition, so it needs to be checked by a GP.

Check if you have acanthosis nigricans

The main symptom of acanthosis nigricans is patches of skin that are darker and thicker than usual.

They can appear anywhere on the body.

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Benedicte Desrus / Alamy Stock Photo

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CID, ISM /SCIENCE PHOTO LIBRARY

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ANDRE LABBE, ISM/SCIENCE PHOTO LIBRARY

The patches often appear gradually without any other symptoms.

Sometimes the skin may be itchy.

Causes of acanthosis nigricans

The most common cause of acanthosis nigricans is being very overweight.

Other causes include:

• type 2 diabetes
• conditions that affect hormone levels – such as Cushing's syndrome, polycystic ovary syndrome or an underactive thyroid
• taking certain medicines – including steroids or hormone treatments like the contraceptive pill
• in rare cases, cancer – usually stomach cancer
• in rare cases, a faulty gene inherited from your parents

Sometimes acanthosis nigricans happens in healthy people with no other conditions. This is more common in people with dark skin.

Treating acanthosis nigricans

Once your GP knows what's causing the condition, they can recommend the best treatment.

The patches should fade over time once the cause is treated.

If you're very overweight, your GP may recommend losing weight.

Depending on the cause, they may also recommend:

• medicine to balance your hormones
• medicine to balance your insulin levels
• changing your medicine to one that doesn't cause the patches

There's no specific treatment for the patches. A skin specialist (dermatologist) may be able to suggest treatments to improve their appearance, but finding and treating the cause is usually recommended first.