First, What Exactly Is Acanthosis Nigricans?

Acanthosis nigricans is not simply a change in skin colour.

It involves a change in both colour and texture.

The skin may become:

• darker than the surrounding skin
• thicker
• coarser
• velvety in texture
• more prominent within folds or creases

The borders may not be sharply defined.

According to Mayo Clinic, common locations include the back of the neck, armpits and groin.

The condition often develops gradually.

Some affected areas may itch, develop an odour or occur alongside skin tags.

The change can initially resemble ordinary hyperpigmentation.

But the texture is an important clue.

Acanthosis nigricans is not simply darker skin—it is typically a combination of darkening, thickening and a velvety surface.

Why Doesn't It Wash or Scrub Away?

Because acanthosis nigricans is not surface dirt.

The appearance reflects changes in the skin itself.

Dermatology literature describes thickening of the outer skin layers and changes in the skin surface that contribute to the characteristic velvety appearance.

This is why repeated washing or scrubbing does not remove it.

Aggressive rubbing may simply irritate the skin further.

Could a Dark Neck Be Something Else?

Yes.

Darkening around the neck or other body folds can have causes other than acanthosis nigricans.

Depending on the appearance and history, clinicians may consider other skin conditions or causes of pigmentation such as:

• friction-related changes
• post-inflammatory pigmentation
• eczema or contact irritation
• certain infections
• other dermatological conditions

That is why colour alone should not be used to diagnose AN.

The combination of location, thickening, texture, progression and the wider clinical picture matters.

Why Is Acanthosis Nigricans Linked to Insulin Resistance?

To understand the connection, we need to look beyond blood glucose.

When cells become less responsive to insulin, the pancreas may compensate by producing more insulin.

This can lead to hyperinsulinemia—higher-than-usual circulating insulin levels.

Blood glucose may still remain relatively normal for some time because the pancreas is working harder to compensate.

One proposed mechanism is that persistently elevated insulin concentrations may activate insulin-like growth factor-1 (IGF-1) signalling in skin cells such as keratinocytes and dermal fibroblasts.

This may encourage cellular growth and contribute to the thickened, velvety appearance seen in AN.

This mechanism is biologically plausible and supported in the dermatology literature, but it should still be understood as a proposed mechanism rather than a complete explanation for every case.

The skin may therefore reflect part of the underlying metabolic environment—but it cannot tell us the full story on its own.

How Strong Is the Link With Insulin Resistance?

The relationship is well recognized.

Insulin resistance is one of the most common associations of acanthosis nigricans, particularly when AN occurs alongside obesity or other metabolic risk factors.

Mayo Clinic notes that most people with acanthosis nigricans have also developed insulin resistance.

NCBI StatPearls also identifies insulin resistance and diabetes among the conditions most commonly associated with AN.

Dermatology reviews describe AN as a useful clinical marker associated with hyperinsulinemia and insulin resistance.

But AN does not replace metabolic assessment.

It is also important to remember the opposite:

many people with insulin resistance do not have acanthosis nigricans.

Does Acanthosis Nigricans Mean “I Am Insulin Resistant”?

Not automatically.

Acanthosis nigricans is strongly associated with insulin resistance, but it remains a clinical sign rather than a diagnostic test.

AN can occur in association with:

• insulin resistance
• obesity
• type 2 diabetes
• PCOS and other endocrine conditions
• certain medications
• some inherited syndromes
• rarely, internal malignancy

So the correct response is not:

“I can see this skin change, therefore I have diabetes.”

It is:

“This is a recognised clinical clue. Is there an underlying cause that should be assessed?”

Can Acanthosis Nigricans Appear Before Diabetes?

It can.

Insulin resistance may begin before blood glucose reaches the diabetes range.

During this stage, the pancreas may produce more insulin to compensate for reduced insulin sensitivity.

Mayo Clinic lists darkened skin in areas such as the neck, armpits and groin among possible signs seen in people with prediabetes.

But it is important not to reverse that statement.

Darkened skin on the neck is not proof of prediabetes.

Nor does every person with prediabetes develop acanthosis nigricans.

AN may simply provide a reason to ask whether glucose or broader metabolic screening is appropriate.

If You Notice AN, What Else Is Worth Looking At?

No single clue should be interpreted in isolation.

If you have what appears to be acanthosis nigricans, consider whether other metabolic clues or risk factors are also present.

• increasing waist circumference or central fat
• skin tags
• family history of type 2 diabetes
• higher fasting glucose
• higher HbA1c
• high triglycerides
• low HDL cholesterol
• high blood pressure
• PCOS or irregular menstrual cycles
• signs of androgen excess such as increased facial or body hair or acne
• history of gestational diabetes

Several clues occurring together may make metabolic assessment more relevant.

But AN itself remains only one part of that picture.

Why Is Acanthosis Nigricans Particularly Relevant to Women With PCOS?

Because metabolic and reproductive health can intersect through insulin resistance.

PCOS is commonly associated with insulin resistance in many affected women.

Women may also have features of androgen excess, such as:

• increased facial or body hair
• acne
• irregular or absent periods
• scalp-hair changes

The Society for Endocrinology Clinical Practice Guideline for evaluating androgen excess in women identifies acanthosis nigricans and skin tags among clinical features that can signify insulin resistance.

But AN is not a defining feature of PCOS, and its presence does not establish the diagnosis.

In women with PCOS, AN may reflect the metabolic component of the condition, particularly when other signs of insulin resistance are also present.

In a relatively lean woman, unexplained or extensive AN may sometimes prompt clinicians to consider less common endocrine or genetic causes of insulin resistance, depending on the wider clinical picture.

Can Acanthosis Nigricans Look Different on Different Skin Tones?

Yes.

The word “dark” can be misleading if people expect the condition to have one universal colour.

The degree and appearance of colour change can vary with a person's natural skin tone.

That makes texture particularly useful.

Look for the combination of:

• a colour change
• thickening
• a velvety or coarse texture
• location within a characteristic fold or crease

It should not be diagnosed from colour alone.

I Think I Have Acanthosis Nigricans. What Should I Actually Do?

The first step is not to bleach, scrub or aggressively exfoliate the area.

The first step is to determine whether the skin change really is acanthosis nigricans and, if so, why it has developed.

Depending on the examination, symptoms and risk factors, a healthcare professional may consider:

• your medical and family history
• medications
• waist circumference and weight-related measures where relevant
• blood pressure
• HbA1c and/or fasting plasma glucose
• a lipid profile or broader metabolic assessment when appropriate
• features of PCOS or another endocrine condition

Not everyone with a suspected dark patch needs extensive metabolic testing.

Testing should be guided by the clinical picture.

Measures such as fasting insulin or HOMA-IR may be used in selected settings, but they are not universally required or standardized diagnostic tests for insulin resistance.

A dermatologist may also help confirm the diagnosis if the skin appearance is uncertain.

If Insulin Resistance Is the Cause, Can the Skin Improve?

It may.

Management depends on the underlying cause.

When AN is associated with insulin resistance or obesity, addressing the underlying metabolic condition may gradually improve the skin.

Depending on the individual, a clinician may recommend appropriate:

• physical activity
• nutrition changes
• weight management where medically relevant
• management of abnormal glucose levels, if present
• treatment of an underlying hormonal condition such as PCOS
• medication when clinically indicated

Dermatological treatments may sometimes improve texture or appearance.

But cosmetic treatment does not substitute for addressing the underlying cause.

Changing the appearance of the skin is not the same as correcting a metabolic abnormality.

When Does Acanthosis Nigricans Need Prompt Medical Assessment?

Most cases are associated with metabolic, endocrine, medication-related or inherited causes.

Rarely, sudden and extensive acanthosis nigricans can be associated with an internal malignancy.

The important point is not to assume cancer from a dark patch of skin.

Instead, sudden, rapidly progressive, extensive or otherwise unusual AN—particularly in an adult—should be medically assessed.

Other concerning features may include unusual distribution, intense itching, mucosal involvement or unexplained weight loss.

The appropriate response is clinical evaluation, not self-directed cancer testing.

Myths Worth Avoiding

Myth: “A dark neck means poor hygiene.”

Fact: Acanthosis nigricans involves changes in colour, thickness and texture of the skin. It does not result from failing to wash properly.

Myth: “Every dark patch in a body fold is acanthosis nigricans.”

Fact: No. Friction, inflammation, dermatitis, pigmentation changes and other skin conditions can produce similar appearances.

Myth: “If I have acanthosis nigricans, I definitely have diabetes.”

Fact: AN is associated with insulin resistance and diabetes, but it is not a diabetes diagnostic test.

Myth: “If I don't have AN, I cannot be insulin resistant.”

Fact: Insulin resistance can occur without acanthosis nigricans.

Myth: “Only women with obesity can develop it.”

Fact: Obesity-associated insulin resistance is common, but AN can also occur in relatively lean people and with other endocrine, medication-related, inherited or rare conditions.

Myth: “Lightening the skin treats the cause.”

Fact: Cosmetic improvement does not necessarily correct insulin resistance or another underlying condition.

Diafemme Perspective: Don't Just Look at the Colour—Ask Why the Skin Changed

Women frequently notice changes in their skin long before they think of themselves as having a metabolic problem.

A darker neck may be treated as pigmentation.

An underarm change may be blamed on deodorant, shaving or friction.

The instinct may be to scrub harder or search for a lightening cream.

But acanthosis nigricans asks a different question:

Why has the skin changed?

For many people, the answer may involve insulin resistance.

For some women, AN may appear alongside central fat, skin tags, irregular cycles, PCOS or abnormal glucose.

For others, another dermatological, hormonal or medication-related cause may need to be considered.

The skin itself cannot provide the complete diagnosis.

But sometimes, a skin change can be a reason to look more closely at overall health.

Frequently Asked Questions

What does acanthosis nigricans look like?

It typically appears as darker, thicker skin with a velvety texture, usually in body folds such as the back of the neck, armpits or groin.

Is acanthosis nigricans a sign of insulin resistance?

It is commonly associated with insulin resistance, especially when it appears alongside other metabolic risk factors. However, AN itself is not a diagnostic test for insulin resistance.

Does acanthosis nigricans mean I have diabetes?

No. It can occur with insulin resistance before diabetes develops, and it can also have other causes. Appropriate assessment is more useful than assuming diabetes from the skin finding alone.

Can prediabetes cause dark skin on the neck?

Acanthosis nigricans can occur in people with insulin resistance or prediabetes, but darkened skin on the neck is not proof of prediabetes. A clinician can assess the skin and decide whether tests such as HbA1c or fasting glucose are appropriate.

Can you wash acanthosis nigricans off?

No. AN reflects changes in the skin rather than surface dirt. Aggressive scrubbing does not treat the underlying process and may irritate the skin.

Can women with PCOS develop acanthosis nigricans?

Yes. In women with PCOS, AN may reflect the metabolic component of the condition, particularly when insulin resistance is also present.

Can a thin woman have acanthosis nigricans?

Yes. AN can occur in relatively lean people. Depending on the wider clinical picture, unexplained or extensive AN may prompt evaluation for endocrine, genetic or other causes.

Can acanthosis nigricans improve?

It may improve when its underlying cause is treated, although improvement can be gradual and may be incomplete.

When should acanthosis nigricans be medically assessed?

Persistent or unexplained skin changes should be assessed when the diagnosis is uncertain. Sudden, rapidly developing or unusually extensive AN particularly deserves medical evaluation.

Diafemme's Takeaway

Acanthosis nigricans usually appears as:

darkened + thickened + velvety skin, especially in body folds.

It is commonly associated with insulin resistance and may be present before diabetes is diagnosed.

But it is not a test for insulin resistance, prediabetes or diabetes.

Do not diagnose yourself from the mirror.

And do not dismiss persistent skin changes simply as dirt or pigmentation.

If the skin change is persistent, spreading, rapidly developing or difficult to identify, arrange a clinical assessment rather than repeatedly scrubbing or using bleaching products.

Depending on your symptoms and risk factors, a healthcare professional may examine the skin and consider appropriate glucose or metabolic testing.

Most cases are related to metabolic, endocrine, medication-related or inherited causes.

Rare causes require assessment mainly when the presentation is sudden or unusual.

Sometimes a skin change is simply a skin change. Sometimes it is a reason to look more closely at overall health.