Acanthosis Nigricans: What Clears the Dark Patches, and What GLP-1s Do

Acanthosis nigricans means dark, thickened, velvety patches, usually at the nape, under the arms or in other skin folds. In most people they are a visible sign of too much insulin in the blood.^[1][6] They often fade when the insulin problem eases, and weight loss is the most reliable way to get there: after weight-loss surgery, the patches cleared in 86.5% of patients in the largest study.^[13] No trial has tested Ozempic, Wegovy, Mounjaro or Zepbound for it. The evidence for GLP‑1 drugs is one patient survey with 12 relevant respondents and a few case reports. Metformin trials are small and short, and creams lighten the skin without fixing the cause. One rule overrides all of this: patches that appear suddenly and spread fast need a doctor, because rarely they signal cancer.^[2][4]

What acanthosis nigricans is

The name describes the look under a microscope: thickened (acanthotic) skin that is dark (nigricans). On the body it shows up as brown or black patches that feel velvety and thicker than the surrounding skin, most often around the nape and sides of the neck, under the arms and at the groin.^[4] Less often it appears on the knuckles, elbows, lips, palms or soles.^[2] It does not itch or hurt in most people, which is why many first notice it as a “dirty neck” that does not wash off. Scrubbing harder does nothing.

Obesity is the most common cause.^[1][3] The usual explanation is that when the body resists insulin, the pancreas makes more of it, and high insulin levels stimulate growth-factor receptors on skin cells, which thicken and darken.^[6] The same mechanism is proposed for skin tags and for “finger pebbles,” small bumps on the knuckles.^[6] Other causes include polycystic ovary syndrome, thyroid and adrenal disease, a family trait in otherwise healthy people, and certain medicines, among them birth control pills, prednisone and niacin.^[3] A review of drug-induced cases found 13 drugs implicated, with niacin and insulin the most significant.^[28]

How common it is, and what it predicts

In US primary care it is common. Across a national network of practices, 19.4% of 1,730 patients aged 7 to 65 had it, and patients with the patches were twice as likely to have type 2 diabetes (35.4% against 17.6%).^[8] An earlier Southwest study put the rate at 17% for children and 21% for adults. After accounting for age, weight and other risk factors, those with the patches were still about twice as likely to have diabetes.^[7] The American Academy of Dermatology lists people of Native American, African, Caribbean or Hispanic descent as at higher risk.^[3]

Teenagers show the pattern most clearly. When trained staff checked the necks of 1,438 eighth graders in three states, 28.2% had acanthosis nigricans: 39% of Black students, 30% of Hispanic students and 5.4% of white students. Students with the patches were 59% more likely to have an A1C in the prediabetes range and 47% more likely to have impaired fasting or post-meal glucose, after allowing for weight, family history and puberty.^[9] In a UK clinic, young people with the patches had nearly twice the insulin resistance (HOMA-IR 6.4 against 3.7) of young people matched to them for weight and age,^[10] so the patches added information that weight alone did not.

These are cross-sectional studies. They show that the patches travel with high insulin and high blood sugar, not that every child with a dark neck will develop diabetes. A 2026 systematic review of 656 reports found that in studies where every participant had acanthosis nigricans, 67.4% met the full criteria for metabolic syndrome.^[11] For what that cluster of conditions means, see metabolic syndrome.

The American Diabetes Association writes the sign into its screening rules. In children with overweight or obesity, acanthosis nigricans counts as a risk factor that should prompt testing for prediabetes or type 2 diabetes from puberty or age 10, whichever comes first. In adults with overweight it is listed among the conditions linked to insulin resistance that justify testing.^[12] In practice, a child or adult with these patches and extra weight is a candidate for an A1C or glucose test. What the results mean is covered in prediabetes and type 2 diabetes.

Weight loss: the best evidence for clearing it

Patient guidance from MedlinePlus and the American Academy of Dermatology says the same thing: the patches often fade when the cause is treated, and in people with obesity that means losing a significant amount of weight.^[2][3] The studies that measured it are mostly of weight-loss surgery, because surgery produces large, documented weight loss.

All three surgical studies saw the skin improve.^[13][14][15] In the smaller Chinese study it improved within months, alongside lower insulin resistance, which fits the idea that the patches track insulin rather than weight for its own sake.^[14] Surgery also brought a price: more than half the Thai patients had a bout of hair shedding.^[15] The one randomized study did not use surgery or drugs. A community program on diet, sleep, screen time and activity for young children cut the share of children with acanthosis nigricans by 3.55 percentage points against control communities, a modest but measured change.^[16]

Clearing is not guaranteed. A pediatric review notes that a complete cure is hard to achieve,^[1] and the American Academy of Dermatology warns that getting prediabetes under control may not fully clear the skin.^[5] Thick, long-standing patches can leave some darkening behind.

GLP-1 drugs: plausible, but almost no data

GLP‑1 drugs lower weight and improve insulin sensitivity, so it is reasonable to expect the patches to fade on them. Nobody has run the study. A search of ClinicalTrials.gov lists 24 registered studies of acanthosis nigricans, testing metformin, an SGLT2 drug, chromium, creams, lasers and surgery, and none tests a GLP‑1 drug.^[21] What exists:

• A patient survey. In a 2026 survey of 1,226 patients in a US virtual weight-management program, 12 people on a GLP‑1 said they had acanthosis nigricans before treatment, and 9 of them (75%) reported it improved. The confidence interval runs from 43% to 93%. In the same survey, 14 of 57 people with skin tags (25%) said those improved.^[17] Self-reports from 12 people, with no exam and no comparison group, show only that improvement is possible.
• Case reports in HAIR-AN. HAIR-AN (hyperandrogenism, insulin resistance and acanthosis nigricans) is a severe form of PCOS. In five women given liraglutide, insulin resistance, androgen levels and menstrual cycles improved with little weight loss, but the published summary does not report on the skin.^[18] One child treated with metformin plus liraglutide had her acanthosis nigricans improve alongside her weight and blood sugar.^[19]
• A systematic review of GLP‑1 drugs in existing skin disease grouped HAIR-AN with psoriasis and hidradenitis suppurativa as conditions with reported improvement, and called for larger prospective studies.^[20]

If a GLP‑1 drug produces substantial weight loss and lowers insulin, the skin would be expected to follow, as it does after surgery. That is inference from the surgical data, not a measured effect of the drug. Acanthosis nigricans is not an approved use for any GLP‑1 drug, and on its own it is not a reason to start one. For PCOS, where these drugs are used off-label, the trial evidence is set out in GLP-1 drugs for PCOS. For teenagers, see GLP-1 drugs in teenagers and what changed in the teenagers’ bloodwork.

Metformin: small trials, no placebo

Metformin is the drug most often tried, because it lowers insulin. Its trials are small, short and compare it with other drugs rather than with a placebo.

In the largest trial, people on metformin lost about 2 kg over 12 weeks and their skin grades improved, but so did the skin of people on pioglitazone.^[22] Without a placebo group, neither trial can separate the drug from time, attention and weight change.^[22][23] The smallest found no effect on severity.^[24] A systematic review of metformin across skin conditions called the results for acanthosis nigricans mixed.^[25] Metformin is a reasonable choice when blood tests show prediabetes or diabetes anyway. For people already on a GLP‑1, how the two drugs combine is covered in metformin and a GLP-1 together.

Creams, peels and lasers

Skin treatments lighten and soften the patches but do not touch the insulin problem underneath. The American Academy of Dermatology notes that none of them was designed for acanthosis nigricans.^[5] Two systematic reviews give the best summary:

• Topical tretinoin (a prescription retinoid) has the strongest support. One review graded it A, its strongest recommendation.^[27] Another, of seven randomized trials with 268 people, found it the most effective for dark pigment, especially on the neck.^[26]
• Urea cream (10–20%) helped, particularly with redness. Salicylic acid 10% worked about as well as urea, with mild dryness or peeling.^[26]
• Chemical peels: a 15% trichloroacetic acid peel beat a 35% glycolic acid peel.^[26]
• Adapalene gel and fractional CO2 laser received a B grade.^[27] MedlinePlus also lists ammonium lactate and hydroquinone creams and laser treatment.^[2]

The trials ran 8 weeks to 2 months, and side effects were mild stinging, dryness or peeling that resolved.^[26] Nothing in them shows what happens after stopping. If the insulin resistance remains, the patches can be expected to return. A dermatologist can choose the strength and watch for irritation.

Skin tags: the same signal, weaker

Skin tags (acrochordons) often appear beside acanthosis nigricans on the neck and in the armpits, and the same high-insulin mechanism is proposed for both.^[6] In 55 children diagnosed with skin tags at one US dermatology clinic, obesity was twice as common as in a national comparison sample (42% against 21%) and type 2 diabetes eight times as common (4.8% against 0.6%).^[29] Skin tags are also common in people with no metabolic problem, so they are a weaker signal on their own. They improved in some patients after weight-loss surgery,^[15] but only a quarter of GLP‑1 users with skin tags in the 2026 survey reported improvement, against three quarters of those with acanthosis nigricans.^[17]

When dark patches need a doctor quickly

The common form develops slowly, over months or years.^[4] A rare form, malignant acanthosis nigricans, comes on fast and can be a sign of an internal cancer, especially of the stomach, colon or liver.^[2][3] The American Academy of Dermatology advises booking an appointment immediately if the patches appear suddenly.^[4] Warning features:

• Patches that appear or spread over weeks rather than years, especially in an adult who has not gained weight.
• Involvement of the lips, inside of the mouth, palms or soles, which MedlinePlus notes is more common in people with cancer.^[2]
• A sudden shower of warty spots (seborrheic keratoses), a sign classically linked with internal cancer,^[6] or weight loss you did not try for.
• Symptoms beyond the color and texture change. MedlinePlus notes the usual form causes none.^[2]

MedlinePlus advises anyone who develops thick, dark, velvety skin to contact a provider.^[2] Diagnosis is usually by looking; the useful tests are for blood sugar and, depending on the picture, thyroid, androgen and other hormone levels.^[5] For itching and rashes that do start on a GLP‑1, a different problem, see GLP-1 skin sensitivity, rash and itching. Women with patches plus irregular periods, acne or excess hair should ask about PCOS.

What to ask a clinician

1. Should I have an A1C or glucose test? With extra weight, the ADA standards say yes.
2. Could a medicine I take be causing this? Bring a list that includes niacin, steroids, hormones and insulin.
3. Do I need hormone tests? Especially with irregular periods, acne or excess hair.
4. Is a prescription cream worth trying while I work on the cause? Tretinoin has the best evidence.
5. For a child: what is the plan for diabetes screening, and how often should it be repeated?