Acanthosis nigricans is a skin condition that causes dark, velvety patches to form in body folds and creases. It isn’t a disease on its own but rather a visible signal that something else is happening inside your body, most commonly insulin resistance. The patches are harmless, but the underlying cause often needs attention.
What It Looks and Feels Like
The hallmark is a patch of skin that looks darker than the surrounding area and feels thicker, with a soft, velvety texture. The darkening has blurry, poorly defined borders rather than a sharp edge. Over time, flat discolored areas can progress into raised, palpable patches. Most people notice the changes gradually and don’t experience pain, though some people report mild itching.
The patches show up where skin rubs against skin. The most common locations are the back of the neck, the armpits, and the groin. In children, the back of the neck is by far the most frequent spot. Less commonly, it can appear around the nipples, on the elbows and knees, or on the knuckles. In rare cases, it develops on mucous membranes inside the mouth, nose, or throat.
Many people mistake acanthosis nigricans for dirt or poor hygiene because the patches look like skin that hasn’t been washed properly. Scrubbing won’t help. The discoloration comes from changes within the skin itself, not from anything on its surface.
Why It Happens
The most common driver is too much insulin circulating in the blood, a state called hyperinsulinemia. When your body becomes resistant to insulin (meaning cells stop responding to it normally), the pancreas compensates by producing more. That excess insulin spills over and stimulates growth-factor receptors on skin cells, causing them to reproduce faster than usual. The result is thicker, darker skin in areas prone to friction.
Because insulin resistance sits at the center of several metabolic conditions, acanthosis nigricans often appears alongside obesity, type 2 diabetes, and polycystic ovary syndrome (PCOS). It can also show up during the prediabetes stage, sometimes years before blood sugar levels rise enough to qualify as diabetes. That’s what makes it such a useful early warning sign.
Other Causes Beyond Insulin Resistance
While insulin resistance accounts for most cases, a few other triggers exist. Certain medications can cause drug-induced acanthosis nigricans. A systematic review identified 13 drugs linked to the condition, with nicotinic acid (a form of niacin used for cholesterol) and injected insulin being the two most common culprits. Hormonal conditions like thyroid disorders and adrenal problems can also play a role.
In rare cases, acanthosis nigricans signals an internal cancer. This malignant form is distinct: it comes on suddenly, spreads extensively (sometimes covering the palms, soles, and inside of the mouth), and progresses quickly. Gastric cancer is the most frequently associated tumor, accounting for roughly 56 to 61 percent of malignant cases. Cancers of the liver, pancreas, lung, breast, and colon have also been linked. When the cancer is treated, the skin patches tend to improve, and if they reappear later, it can signal a recurrence.
What It Means in Children
Acanthosis nigricans is increasingly common in children, closely tracking the rise in childhood obesity. Research has shown that the severity of the skin changes correlates with the degree of insulin resistance. Children with more pronounced darkening and thickening on the neck (scored at 3 or higher on clinical scales) have a significantly increased risk of insulin resistance, with studies reporting 84 percent specificity for that cutoff.
Because of this strong link, pediatric guidelines recommend using visible acanthosis nigricans as a trigger for metabolic screening. For a parent, a dark velvety patch on the back of a child’s neck is worth bringing up at a checkup. It may be the earliest visible clue to prediabetes or metabolic syndrome, and catching it early opens a wider window for lifestyle changes to make a real difference.
How It’s Diagnosed
A doctor can usually identify acanthosis nigricans just by looking at it. The combination of location, texture, and color pattern is distinctive enough that a skin biopsy is rarely needed. The more important step is figuring out what’s driving it. That typically means blood tests to check fasting blood sugar, insulin levels, and hemoglobin A1C (a marker of average blood sugar over three months). Depending on the situation, your doctor may also evaluate thyroid function or screen for PCOS.
If the patches appear suddenly, are widespread, or involve unusual areas like the palms or mouth, further testing to rule out an underlying cancer may be warranted. This malignant form is uncommon but serious enough that rapid onset should never be dismissed as cosmetic.
Treatment Options
The most effective treatment targets whatever is causing the skin changes, not the skin itself. For the majority of people, that means addressing insulin resistance through weight loss and increased physical activity. Reducing body weight in obesity-related cases can resolve the thickened patches entirely, and correcting hyperinsulinemia visibly reduces the darkened areas over time.
When lifestyle changes aren’t enough, insulin-sensitizing medications can help. In one clinical trial, patients who took metformin three times daily for three months showed significant improvement in acanthosis nigricans on the neck and armpits compared to a placebo group. The skin improvement tracked with better insulin sensitivity.
For people who want to address the cosmetic appearance directly, several topical treatments can help lighten and smooth the affected skin:
- Topical retinoids are considered a first-line option. In one study of 30 patients, all showed clinical improvement within just 14 days of application. Adapalene, another retinoid, has been shown to reduce skin darkening in children.
- Vitamin D-based creams have shown improvement in some patients after about three months of twice-daily use.
- Chemical peels using exfoliating acids have improved the condition in small studies.
- Salicylic acid and urea-based creams have produced variable but sometimes helpful results.
Oral retinoids can also be effective for extensive cases, but the skin changes tend to return once the medication is stopped. This reinforces why treating the root cause matters more than treating the skin alone. If insulin resistance or obesity is still present, the patches will likely come back regardless of what you put on your skin.
What to Watch For
Most acanthosis nigricans develops gradually and signals a metabolic issue that can be managed. The patches themselves are not dangerous. But a few patterns deserve prompt attention: skin changes that appear suddenly and spread rapidly, involvement of the palms or soles, patches inside the mouth, or acanthosis nigricans in someone who is not overweight and has no known metabolic condition. These features raise the possibility of the rare malignant form, which is most often linked to abdominal cancers and carries an average survival under two years after diagnosis.
For the far more common insulin-resistant form, the skin is doing you a favor. It’s making an invisible metabolic problem visible, often before diabetes develops. Treating it early, primarily through lifestyle changes, can improve both the skin and your long-term metabolic health.