What causes acanthosis nigricans?

Acanthosis nigricans sometimes occurs in people who are otherwise in good health, particularly dark-skinned people of African descent.

However, in most cases it's a sign of an underlying problem or condition such as obesity , diabetes or abnormal hormone levels.

Some of the main causes of acanthosis nigricans are

Obesity

Acanthosis nigricans is usually the result of obesity. This is known as obesity-associated acanthosis nigricans.

It occurs because obesity can cause insulin resistance (when the body is unable to properly use the hormone insulin), which may lead to high levels of insulin in the blood, affecting the skin cells.

Insulin resistance can also cause type 2 diabetes , so acanthosis nigricans can be an early sign that you have diabetes or are at risk of developing the condition.

Syndromes and hormone problems

Acanthosis nigricans is sometimes associated with an underlying syndrome or hormone problem, such as:

• polycystic ovary syndrome a condition that affects how a woman's ovaries work,which cancause excessive body hair , irregular periods , infertility , acne and weight gain
• Cushing's syndrome symptoms such as weight gain, bruising and stretch marks caused by very high levels of the hormone cortisol in the body
• acromegaly wherethe body produces too much growth hormone, leading to the excess growth of body tissues over time
• underactive thyroid (hypothyroidism) where your thyroid gland does not produce enough hormones, causing symptoms such as tiredness and weight gain

This type of acanthosis nigricans is known as syndromic acanthosis nigricans.

Medication

Acanthosis nigricans is sometimes triggered by medicines, including insulin, corticosteroids , and hormone treatments such as human growth hormone or the contraceptive pill .

This is known as drug-induced or medication-associated acanthosis nigricans.

Genes

In rare cases, acanthosis nigricans can be caused by a faulty gene inherited directly from your parents. This is known as familial or benign genetic acanthosis nigricans.

This type is usually passed on in an autosomal dominant pattern, which means it can be passed on if only one of your parents carries the faulty gene.

Cancer

If the dark skin patches come on suddenly and spread quickly, it may be a sign you have cancer (usually stomach cancer ). This is known as malignant acanthosis nigricans.

This is a rare condition thattends to affectmiddle-aged or elderly people, regardless of their weight or ethnic background.

The patches are more severe and the mouth, tongue and lips may also be affected. The skin may also become irritated and itchy.