Acanthosis Nigricans: Symptoms, Causes, Diagnosis, and Treatment (2026 Guide)
Updated: 2 days ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: September 2026
TL;DR
Acanthosis nigricans (AN) is a skin condition that causes light-brown-to-black patches with a velvety texture, most often on the skin folds of the neck, armpits, groin, and under the breasts. It's not contagious or dangerous by itself — but it can be a sign of elevated insulin from prediabetes, diabetes, or obesity, so it shouldn't be ignored. Washing won't remove it; it typically appears slowly over months or years and is diagnosed by visual exam, with blood work to find the cause. Treating the underlying condition — especially weight loss and blood sugar control — usually clears or improves the skin, and the outlook is excellent: people live normal, healthy lives with AN. One warning matters most: patches that appear suddenly should be checked right away, as rapid onset is rarely linked to cancer.
Quick Answer
What is acanthosis nigricans?
A skin disorder causing dark brown-to-black patches with a velvety texture, most often on the neck, armpits, groin, and under the breasts.
It's not contagious and isn't dangerous itself, but it can signal prediabetes, diabetes, obesity, or hormonal conditions.
It won't wash off, won't go away on its own, but usually clears or improves when the underlying cause — especially high insulin — is treated.
Patches that appear suddenly should be evaluated immediately, since rapid onset is rarely a cancer warning sign.
What Is Acanthosis Nigricans?
Acanthosis nigricans (pronounced "a-can-THO-sis NIH-grih-cans") is a skin disorder that results in light-brown-to-black spots on the skin. The markings can look like a dirt stain or spot you might try to scrub off in the shower — but washing will not remove acanthosis nigricans. It's a change in the skin itself, not something sitting on top of it.
The characteristic patches have a velvety texture and can appear anywhere on the body. They most often show up on the skin folds of the neck, armpits, and groin, and under the breasts.
Two reassuring facts come first: AN isn't contagious — you can't pass it to others or catch it from anyone — and it isn't dangerous on its own. The reason it deserves attention is that in some cases, it can be a sign of an underlying condition that needs treatment, such as diabetes.
What Are the Symptoms?
The signs of acanthosis nigricans develop gradually, appearing slowly over months or even years:
Dark patches: Patches of brown or black skin, looking like a stain
Velvety texture: The affected skin feels soft and velvety to the touch
Skin tags: Small skin growths can appear in the same areas
Itchiness: The patches may itch
Odor: The skin patches may smell foul
The most important timing rule: symptoms tend to appear slowly. If these signs appear suddenly, see a dermatologist — a rapid onset may be a sign of cancer, though this is rare.
What Causes Acanthosis Nigricans?
AN has many possible causes, but they cluster around a common theme: most involve elevated insulin levels in the blood.
Elevated insulin (most common): Obesity, prediabetes, or diabetes — excess insulin stimulates skin cell growth
Congenital: Present from birth
Genetics: Family members have AN
Certain medications: Including birth control pills and steroids
Hormonal conditions: Thyroid disease, Addison's disease, hypothyroidism, and other pituitary disorders
Growth hormone therapy: Hormone treatment can trigger it
Who Is at Higher Risk?
Anyone can develop acanthosis nigricans, including otherwise healthy people. You may be at higher risk if you:
Have excess weight or obesity
Have a family history of AN
Are of Native American, African, Caribbean, or Hispanic descent
Have darker skin
How common is it? AN is a rare disease, and researchers don't know exactly how often it occurs in America. However, one study of adults with obesity found that at least 50% of those who weighed double their ideal body weight showed signs of acanthosis nigricans.
Does Acanthosis Nigricans Mean I Have Diabetes?
AN doesn't always mean you have diabetes or prediabetes — but it can be a sign of diabetes, so talk to your healthcare provider if you notice the patches. Prediabetes means you have early signs but haven't yet developed diabetes; your provider can discuss steps to reduce your risk. If you do have diabetes, you can discuss treatment options together.
How Is Acanthosis Nigricans Diagnosed?
Diagnosis is often straightforward. Your healthcare provider will:
Take your history — discussing your symptoms and medical background
Perform a physical exam — these two steps are often enough to diagnose AN
Order blood work — to confirm or rule out underlying conditions such as diabetes
Occasionally biopsy the skin — a skin biopsy (taking a sample of skin tissue) is used on rare occasions when the diagnosis isn't straightforward
Symptom discussion + medical history: Pattern, timing, medications, family history
Physical exam: The appearance and texture of the patches — often sufficient
Blood work: Underlying conditions, especially diabetes and insulin levels
Skin biopsy: Rare cases where the diagnosis isn't clear
How Is Acanthosis Nigricans Treated?
Will it go away on its own? No — but you don't always need medical treatment. If no underlying condition is causing your AN, you can simply decide whether you want to treat the dark patches for cosmetic reasons.
Is it reversible? People typically see good results after treatment. The skin clears, although the dark spots may not go away completely.
How is it treated? Treatment depends on the cause. If AN is due to an underlying condition such as diabetes or a hormonal condition, treating the condition treats the skin.
Weight loss, exercise, healthy diet: Reduces insulin levels — patches may disappear completely
Treating the underlying condition: Managing diabetes, thyroid problems, or other hormonal causes
Prescription creams: To lighten the darkened area
Laser therapy or dermabrasion: To reduce skin thickness
Antibiotics: To get rid of odor or discomfort
Retinoids: To help clear the skin
Stopping certain medications: Removing the drug that triggered AN
A word of caution: do not use over-the-counter skin care products to treat the dark spots without consulting a healthcare provider. These products may not work and may even irritate your skin, worsening the condition.
If your AN is related to elevated insulin, managing your weight and eating a healthy diet can help prevent or reduce the dark spots.
What Is the Outlook?
Acanthosis nigricans isn't dangerous or harmful, and people can live normal, healthy lives with AN. The condition itself is treatable, and most people see good cosmetic results once the cause is addressed.
What matters most is managing the conditions that may be causing it — diabetes, obesity, and hormonal conditions. And if the dark patches appear suddenly, see your healthcare provider immediately, since the sudden appearance may be a sign of cancer.
Can Acanthosis Nigricans Be Prevented?
Prevention focuses on the most common drivers. If obesity is causing AN, you can help prevent the condition through weight management. A diet that keeps your blood sugar (insulin) levels in check can also help prevent AN.
Weight management: Reduces the insulin resistance that most often drives AN
Balanced diet for blood sugar: Keeps insulin levels in check
Managing related medical conditions: Treating thyroid problems and diabetes reduces the trigger
Avoiding triggering medications: Some birth control pills and other drugs can cause or worsen AN
Living With It
Any time you notice changes in your skin, see your healthcare provider or a dermatologist. Small markings or changes may seem insignificant, but they may indicate a problem — and acanthosis nigricans can be a sign of prediabetes or diabetes. Talk to your provider so you can get the proper care.
Questions to ask your healthcare provider: Could my skin patches be acanthosis nigricans? Should I be tested for prediabetes or diabetes? What is causing my patches? What treatment do you recommend for my skin? Will the patches go away completely?
Conclusion
Acanthosis nigricans is a treatable skin condition that causes dark, velvety patches in the skin folds of the neck, armpits, groin, and under the breasts. It can't be washed off, won't go away on its own, and isn't dangerous by itself — but it's worth taking seriously, because more often than not, it's the skin's way of signaling elevated insulin from obesity, prediabetes, or diabetes.
The two takeaways that matter most: treat the cause, and the skin follows — weight loss, blood sugar control, and managing hormonal conditions usually clear the patches, sometimes completely; and speed matters — patches that build gradually over months are the typical, benign pattern, while patches that appear suddenly deserve immediate evaluation.
Noticed dark, velvety patches on your neck, armpits, or groin that won't wash off? Book an appointment with your healthcare provider or a dermatologist — a simple visual exam plus blood work can confirm what's going on, check your blood sugar, and set up a treatment plan that clears the skin from both directions.
Frequently Asked Questions
What is acanthosis nigricans?
A skin disorder that causes light-brown-to-black patches with a velvety texture, most often on the skin folds of the neck, armpits, groin, and under the breasts. It is pronounced "a-can-THO-sis NIH-grih-cans."
Is acanthosis nigricans contagious?
No. You can't pass it to others or get it from other people.
Why won't the dark patches wash off?
Because the darkening is the skin itself changing, not dirt on top of it. Washing will not remove acanthosis nigricans.
Does acanthosis nigricans mean I have diabetes?
Not always — it happens to otherwise healthy people too. But it can be a sign of diabetes or prediabetes, so it's worth discussing with your healthcare provider, especially if you have risk factors like excess weight or a family history.
What causes it?
Most commonly, conditions associated with elevated insulin — obesity, prediabetes, and diabetes. Other causes include congenital cases, genetics, certain medications (birth control pills, steroids), hormonal conditions like thyroid disease and Addison's disease, and growth hormone therapy.
Can it go away?
It won't go away on its own, but it usually improves or clears with treatment. Treating the underlying cause — especially weight loss and blood sugar control — often makes the patches fade, sometimes completely, though dark spots may not fully disappear.
When should I worry?
If the dark patches appear suddenly rather than gradually over months, see a healthcare provider or dermatologist immediately — rapid onset is rare but can be a sign of cancer.
References
This article is based on medically reviewed clinical information from Acanthosis Nigricans, which draws on guidance from the American Academy of Dermatology, the National Organization for Rare Disorders, and the American Osteopathic College of Dermatology.
This article is for educational purposes only and is not a substitute for professional medical advice. Dark, velvety skin patches should be evaluated by a healthcare provider, as they can indicate conditions like prediabetes or diabetes that benefit from early treatment.
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