Dark Skin Patches and Skin Tags: What Acanthosis Nigricans Can Signal About Insulin

Have you noticed dark skin patches on the back of your neck, in your armpits, or along skin folds? Maybe you have also spotted a few small, soft skin tags nearby. Many people search for answers about these changes, and the name that often comes up is acanthosis nigricans.

Your skin can reflect what is happening inside your body. Researchers have studied how dark, velvety skin patches and skin tags relate to insulin resistance, a change in how the body responds to the hormone insulin.

In this article, we explain what acanthosis nigricans is, how insulin works, what the research says about the skin-insulin connection, and when it makes sense to talk with a healthcare provider.

What Is Acanthosis Nigricans?

Acanthosis nigricans (say it: ay-can-THOE-sis NIE-gri-cans) is a skin change that makes some areas of skin darker and thicker. According to the American Academy of Dermatology (AAD), the skin may look brown or black and feel velvety. It can also itch or have an odor, and skin tags may form in the same area.

These dark patches on the skin often show up in body folds and creases, such as:

• The back and sides of the neck
• The armpits
• The groin
• Under the breasts
• The elbows, knees, or knuckles

The AAD notes that anyone can develop acanthosis nigricans. It is seen more often in people with higher body weight, people with a family history of it, and people of Native American, African, Caribbean, or Hispanic descent.

How Insulin Works in the Body

To understand the skin connection, it helps to know what insulin does. Insulin is a hormone made by the pancreas, an organ behind your stomach. After you eat, your blood sugar (glucose) rises. Insulin works like a key that helps move glucose out of the blood and into your cells, where it is used for energy.

Insulin resistance happens when cells in the muscles, fat, and liver do not respond to insulin as well as they should. To keep blood sugar in a normal range, the pancreas makes more insulin. Over time, this can lead to higher-than-usual insulin levels in the blood. The medical term for this is hyperinsulinemia (high insulin in the blood).

The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) explains that insulin resistance often has no clear symptoms. A person can have it for years without knowing. That is one reason researchers pay attention to visible signs, like changes in the skin.

The Skin and Insulin Connection: What Research Shows

Why would insulin affect your skin? A 2012 review in Anais Brasileiros de Dermatologia explains one leading idea. When insulin levels stay high, insulin can interact with receptors on skin cells called IGF-1 receptors. This may signal two types of skin cells to grow faster: keratinocytes (cells on the skin's surface) and fibroblasts (cells deeper in the skin). That extra growth can lead to the thick, darker texture of acanthosis nigricans.

The NIDDK notes that some people with prediabetes have darkened skin in the armpits or on the back and sides of the neck. Several studies have looked at this link more closely:

• A 2007 study in the Annals of Family Medicine looked at young people seen in primary care practices. It found that acanthosis nigricans was linked with known risk factors for type 2 diabetes.
• Studies reviewed in 2012 found that, in some groups, more severe acanthosis nigricans was linked with higher insulin resistance scores.

Not every study agrees. Some researchers have suggested that, in certain groups, the skin change may reflect body weight more than insulin resistance on its own. This is why scientists describe acanthosis nigricans as a possible marker, or sign worth noticing, rather than proof of any health condition.

Skin Tags and Insulin: Is There a Link?

Skin tags (medical name: acrochordons) are small, soft growths of skin. They often hang from a thin stalk and are usually harmless. They tend to appear on the neck, in the armpits, and in the groin. These are the same places where acanthosis nigricans often shows up.

Skin tags are very common, especially with age. The 2012 review notes that their frequency rises after age 40. Having a few skin tags is normal for many people.

Researchers have also studied whether having many skin tags relates to insulin. The same review describes studies that found higher insulin levels in people with multiple skin tags compared to people without them. One study it cites found an association between having more than five skin tags and higher insulin resistance scores. Like acanthosis nigricans, skin tags may have more than one cause, and insulin appears to be one factor researchers are still studying.

PCOS and Insulin Resistance

Polycystic ovary syndrome (PCOS) is one of the most common hormone conditions in women of reproductive age. A 2015 review in the Journal of Medicine and Life reports that insulin resistance appears in about 50% to 80% of women with PCOS. It is seen more often in women with higher body weight, but lean women with PCOS can have it too.

Researchers think insulin and reproductive hormones are closely linked in PCOS. High insulin levels may signal the ovaries to make more androgens, which are hormones like testosterone. High insulin may also lower SHBG, a protein that carries these hormones in the blood. This can leave more free testosterone circulating. Researchers believe this may help explain some common PCOS features, such as extra hair growth and acne.

The skin can be part of this picture as well. The same review notes that many women with PCOS show signs of acanthosis nigricans, and that its severity has been linked to the degree of insulin resistance. Still, not everyone with PCOS has insulin resistance or skin changes. Only a healthcare provider can diagnose PCOS.

Other Possible Causes of Dark Skin Patches

Insulin is only one piece of the picture. According to the AAD and the 2012 review, acanthosis nigricans has also been linked with:

• Higher body weight, which the AAD lists as the most common cause
• Family history, since some forms run in families
• Hormone conditions, such as polycystic ovary syndrome (PCOS) and thyroid conditions
• Certain medicines, including corticosteroids, some birth control pills, and high doses of niacin (a B vitamin)
• Cancer, in rare cases, especially when the dark patches appear suddenly and spread quickly

Because there are so many possible causes, a skin change alone cannot tell you what is happening inside your body.

When to Talk With a Healthcare Provider

If you notice new dark, velvety skin patches or a sudden increase in skin tags, it is worth mentioning to a doctor or dermatologist. This is especially true if the changes appear quickly. Only a healthcare provider can look at your skin, review your health history, and decide whether any tests make sense for you.

The NIDDK explains that providers often use blood tests to check blood sugar levels. A direct test for insulin resistance is complex and is mostly used in research settings.

Factors Researchers Study in Insulin Health

Scientists are still learning what drives insulin resistance. The NIDDK notes that genes play a role. Researchers also think that excess body weight and low physical activity are major factors. Other areas of ongoing study include sleep, stress, and overall eating patterns.

Everyone's body is different. A healthcare provider can help you understand which factors may be relevant to your own health.

The Bottom Line

Dark skin patches and skin tags are more than a cosmetic concern for many people. Research has linked acanthosis nigricans and multiple skin tags with insulin resistance, though they can also have many other causes. Learning how insulin works, and what your skin may be signaling, can help you have a more informed conversation with your healthcare provider.

Sources

1. American Academy of Dermatology. Acanthosis nigricans: Signs and symptoms and Acanthosis nigricans: Who gets and causes.
2. National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). Insulin Resistance & Prediabetes.
3. Barbato MT, Criado PR, Silva AK, Averbeck E, Guerine MB, Sá NB. Association of acanthosis nigricans and skin tags with insulin resistance. Anais Brasileiros de Dermatologia. 2012;87(1):97–104.
4. Kong AS, Williams RL, Smith M, et al. Acanthosis nigricans and diabetes risk factors: prevalence in young persons seen in southwestern US primary care practices. Annals of Family Medicine. 2007;5(3):202–208.
5. Dumitrescu R, Mehedintu C, Briceag I, Purcarea VL, Hudita D. The Polycystic Ovary Syndrome: An update on metabolic and hormonal mechanisms. Journal of Medicine and Life. 2015;8(2):142–145.

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