Have you ever noticed dark, velvety patches of skin around your neck, under your arms, or in other body folds and wondered what they mean?

For many people, these skin changes appear gradually and don't cause pain or itching. Because they often develop slowly, they're easy to ignore or mistake for dirt, poor hygiene, or simple skin discoloration. But in some cases, these patches can be a sign that your body is trying to tell you something important.

One possible cause is acanthosis nigricans, a skin condition that is often linked with insulin resistance, obesity, hormonal disorders, certain medications, or, more rarely, other underlying medical conditions.

The good news is that acanthosis nigricans itself is not contagious, and it is not caused by poor hygiene. While it isn't dangerous on its own, it can sometimes be a clue that it's worth discussing your overall health with a healthcare professional.

Let's take a closer look at what it is, why it happens, and when it's a good idea to seek medical advice.

What Is Acanthosis Nigricans?

Acanthosis nigricans is a skin condition that causes areas of skin to become:

•  Darker than the surrounding skin
•  Thicker
•  Velvety in texture

The discoloration may range from light brown to dark brown or gray, depending on a person's natural skin tone.

The affected skin often feels soft or slightly raised rather than rough or scaly.

Where Does It Usually Appear?

The condition most commonly develops in skin folds, including:

•  The back or sides of the neck
•  Under the arms (armpits)
•  The groin
•  Elbows
•  Knees
•  Knuckles
•  Under the breasts

Less commonly, it can appear on:

•  The face
•  Belly button
•  Hands
•  Lips

What Causes Acanthosis Nigricans?

Acanthosis nigricans isn't a disease by itself. Instead, it's often a sign associated with another condition or factor.

1. Insulin Resistance

The most common cause is insulin resistance, a condition in which the body's cells don't respond well to insulin.

To compensate, the body produces more insulin, and high insulin levels may stimulate skin cells to grow more rapidly, leading to thickened, darker patches.

Insulin resistance is commonly associated with:

•  Prediabetes
•  Type 2 diabetes
•  Metabolic syndrome

Not everyone with insulin resistance develops acanthosis nigricans, but the two are frequently linked.

2. Excess Body Weight

People who are overweight or obese are more likely to develop insulin resistance, making acanthosis nigricans more common in this group.

In some individuals, gradual weight loss and improved metabolic health may lead to improvement in the skin changes.

3. Hormonal Conditions

Several hormone-related conditions may increase the likelihood of developing acanthosis nigricans, including:

•  Polycystic ovary syndrome (PCOS)
•  Cushing syndrome
•  Hypothyroidism
•  Other endocrine disorders

4. Certain Medications

Some medications have been associated with acanthosis nigricans, including:

•  High-dose corticosteroids
•  Some hormonal medications
•  High-dose niacin
•  Certain treatments that affect growth hormones

If you notice new skin changes after starting a medication, don't stop taking it on your own. Speak with your healthcare provider.

5. Genetics

In some families, acanthosis nigricans can occur due to inherited genetic factors.

This form is much less common and may appear during childhood without being linked to obesity or diabetes.

6. Rare Medical Conditions

Rarely, acanthosis nigricans can be associated with certain internal cancers, particularly stomach (gastric) cancer.

This form usually develops suddenly, spreads quickly, and may involve unusual locations such as the mouth or palms.

Although this possibility sounds alarming, it's important to remember that most cases are not related to cancer.

Common Symptoms

Besides darker skin, people may notice:

•  Thickened skin
•  Velvety texture
•  Mild itching (occasionally)
•  Slight odor in skin folds
•  Gradual spread over time

Most people have no pain.

Is It Dangerous?

The skin changes themselves are usually harmless.

However, because acanthosis nigricans may be associated with conditions such as insulin resistance or hormonal disorders, it's worth discussing with a healthcare professional, especially if the patches are new or changing.

Treating the underlying cause often helps improve the appearance of the skin over time.

How Is It Diagnosed?

A healthcare provider can often recognize acanthosis nigricans by examining the skin.

Depending on your situation, they may recommend tests such as:

•  Blood sugar (glucose)
•  Hemoglobin A1C
•  Fasting insulin
•  Cholesterol levels
•  Hormone tests

If the appearance is unusual or develops rapidly, additional evaluation may be recommended.

Can It Be Treated?

Treatment focuses on addressing the underlying cause.

For example:

If It's Related to Insulin Resistance

Improving blood sugar control through lifestyle changes or medication, when appropriate, may gradually improve the skin.

If It's Linked to Excess Weight

For some people, gradual weight loss can reduce insulin resistance and help the affected skin lighten over time.

If a Medication Is Involved

A healthcare provider may decide whether changing medications is appropriate.

Never stop a prescribed medication without medical advice.

Skin Care Tips

Although creams alone usually don't treat the underlying cause, these habits may help keep the skin comfortable:

•  Wash gently with mild cleansers.
•  Moisturize regularly.
•  Avoid harsh scrubbing.
•  Wear loose-fitting clothing if friction is an issue.
•  Protect exposed skin from excessive sun exposure.

Avoid trying to scrub the patches away—they are not caused by dirt and vigorous scrubbing may irritate the skin.

When Should You See a Doctor?

Schedule an appointment if:

•  The patches appear suddenly.
•  They spread quickly.
•  They become painful, itchy, or irritated.
•  You also notice increased thirst, frequent urination, or unexplained weight changes.
•  The discoloration appears in unusual areas such as the mouth or palms.
•  You're concerned about diabetes or another underlying health condition.

Early evaluation can help identify any treatable cause.

Can Acanthosis Nigricans Be Prevented?

Not every case can be prevented, but maintaining overall metabolic health may reduce the risk for some people.

Helpful habits include:

•  Eating a balanced diet
•  Staying physically active
•  Maintaining a healthy weight if recommended by your healthcare provider
•  Managing blood sugar if you have diabetes or prediabetes
•  Attending regular medical checkups

Frequently Asked Questions

Is acanthosis nigricans contagious?

No. It cannot be spread from person to person.

Is it caused by poor hygiene?

No. Washing or scrubbing harder will not remove it.

Will the dark patches disappear?

Sometimes they improve after the underlying cause is treated, but changes may take months and can vary from person to person.

Can children develop acanthosis nigricans?

Yes. It can occur in children, particularly those with obesity or insulin resistance. Pediatric evaluation is important to assess for possible underlying causes.

Does everyone with acanthosis nigricans have diabetes?

No. While it is commonly associated with insulin resistance, it can also be related to other conditions or medications, and some people do not have diabetes.

Final Thoughts

Dark, velvety patches of skin can be surprising to discover, but they are not something to ignore. Acanthosis nigricans is often a visible clue that your body may be experiencing changes such as insulin resistance or another underlying condition. While the skin changes themselves are usually harmless, they can provide an opportunity to identify and address health issues early.

If you notice new or changing dark patches, especially around the neck, underarms, or other skin folds, consider scheduling a medical evaluation. A simple conversation with your healthcare provider can help determine the cause and guide appropriate next steps. With proper care and attention to overall health, many people see improvements in both their skin and their long-term well-being.