No matter how hard you scrub in the shower, the back of your neck and your underarms still have a grey-brown band; it feels thick and velvety rather than smooth, and shows up more where collars rub. Many people assume it is “not washed clean” or just a tan, and scrub harder—leaving the skin redder and rougher. This change may well be acanthosis nigricans, one of the more common skin findings in dermatology clinics.
Acanthosis nigricans itself is usually neither painful nor itchy, but it is often seen as a “skin signal” of the body’s metabolic state and may be linked to insulin resistance, weight gain, polycystic ovary syndrome and similar conditions; in a few cases it is related to other systemic illnesses or to medicines. It is easily mistaken for simple pigmentation, so whether further tests are needed should still be assessed in person by a dermatologist.
Key points: Acanthosis nigricans is a grey-brown to dark, thick, velvety change in skin folds (commonly the back and sides of the neck, underarms and groin). It is not caused by poor washing. It is often linked to insulin resistance and weight gain, and may also relate to polycystic ovary syndrome, hormone problems, family tendency or certain medicines; in a few cases it is linked to other illnesses in the body. The focus is finding the underlying cause and supporting it with weight and lifestyle management, which may let the skin improve gradually. If it spreads quickly, covers a wide area or comes with other symptoms, please have a doctor assess it in person, and avoid hard scrubbing or long-term use of whitening products of unknown content.
What is acanthosis nigricans? Why do the neck and underarms turn dark and thick?
Acanthosis nigricans is a skin change in which the surface cells multiply and thicken and pigment increases, producing grey-brown to dark patches that feel rough and velvety, usually in skin folds and areas of friction.
It is currently understood that when insulin levels in the blood stay high for long periods (common with insulin resistance), the excess insulin may stimulate skin cells to multiply, so the neck, underarms and similar areas gradually darken and thicken. In other words, acanthosis nigricans is not about being “dirty”; the skin is reflecting something going on inside the body.
It can occur in children, teenagers and adults. People who have gained weight, have a family history of diabetes or have polycystic ovary syndrome meet it more often; people who are not overweight can also have it, and whether it relates to metabolism must be judged by a doctor.
What are the symptoms of acanthosis nigricans?
Acanthosis nigricans has some typical features. Common signs include:
Changes in colour and texture
The skin goes from a faint dullness to grey-brown, brown or black, and feels thick and velvety. In more marked cases the surface may develop tiny wart-like bumps, and there may be slight flaking or odor (usually from moisture trapped in folds).
Common locations
The back and sides of the neck and the underarms are the usual places, followed by the groin, under the breasts and around the navel; some people also get it on the elbows, knees and knuckles. It is usually symmetrical and can slowly widen.
Usually no clear discomfort, but some situations deserve attention
Most people feel no pain or itch, so it is easy to overlook. If it spreads quickly over a short time, covers a particularly wide area, or comes with itching or obvious thickening of the lips and palms, have a doctor assess it fully as soon as possible.
What causes acanthosis nigricans? Is it just poor washing?
Acanthosis nigricans is not a hygiene problem. Common causes and related conditions include:
- Insulin resistance and weight gain: when the body responds less well to insulin, insulin output may rise; this is a common related factor in adults and teenagers and it appears more easily with weight gain.
- Polycystic ovary syndrome: some women also have irregular periods, acne or excess hair together with acanthosis nigricans, related to insulin and hormone status.
- Diabetes or prediabetes: metabolic problems tied to blood sugar control may come with acanthosis nigricans; whether blood sugar needs testing is decided by a doctor.
- Other hormone problems: for example thyroid or adrenal conditions may in a few cases appear together with acanthosis nigricans.
- Genetic or family tendency: some people have it from childhood and others in the family have the same.
- Certain medicines: a few medicines may be linked to skin changes, so tell your doctor about all medicines and supplements you take, and do not stop any on your own.
- Other illnesses in the body: rarely, acanthosis nigricans that appears suddenly over a wide area and changes quickly may be linked to another illness and needs further assessment by a doctor.
Besides these underlying causes, friction, heat and sweat in the folds can make the skin rougher and darker; but scrubbing hard cannot deal with the underlying cause and may irritate the skin.
How is acanthosis nigricans different from dirt, tinea versicolor and contact dermatitis?
Darkening of the neck and underarms has more than one cause and is often mistaken for “not washed clean”. The table below summarizes common differences for reference only and cannot replace an in-person examination; for small bumps on the neck, see an explanation of skin tags on the neck, and for pale or brown fine-scaly patches on the chest and back, see tinea versicolor: symptoms and care.
| Feature | Acanthosis nigricans | Simple dirt or friction darkening | Tinea versicolor | Pigmentation after contact dermatitis |
|---|---|---|---|---|
| Main location | Folds such as neck, underarms and groin, often symmetrical | Collar and clothing friction areas | Oily areas such as chest, back and shoulders | Where the skin touched a product or object |
| Look and feel | Grey-brown to dark, thick and velvety, with poorly defined edges | Lighter, usually improves with cleansing, smooth to the touch | Pale or brown patches with fine scaling and clear edges | Dullness left after inflammation, which was red, itchy and peeling |
| Common triggers | Insulin resistance, weight, hormones, genetics, certain medicines | Sweat, friction, inadequate cleansing | Yeast overgrowth in hot, humid conditions | Irritants or allergens |
| Sensation | Usually no pain or itch | Usually none | Mild itch or none | Itch and burning during the inflamed stage |
| Approach | Find the cause, manage metabolism and weight, assessed by a doctor | Gentle cleansing and less friction | Confirm the diagnosis, then assessed by a doctor | Find and avoid the trigger, assessed by a doctor |
How do dermatologists examine acanthosis nigricans?
At the visit, the doctor usually asks how long the skin has been dark, how fast it is changing, whether it is spreading, whether your weight has changed recently, whether diabetes runs in the family, whether periods are regular in women, and which medicines and supplements you take.
The doctor then looks at and feels the skin to confirm colour, thickness, surface texture and distribution, and also checks the lips, palms and other areas for changes; in most cases the clinical appearance alone is enough for a judgment.
Because acanthosis nigricans is often tied to metabolic status, the doctor may consider blood tests based on your situation, for example blood sugar, blood lipids, and tests related to insulin resistance or hormones; if the appearance is atypical or changing quickly, further tests or referral to another specialty may follow. Whether these are needed is decided by the doctor based on your situation.
How is acanthosis nigricans managed? Can it improve?
Management focuses on finding and addressing the underlying cause, then adding local skin care according to how the skin looks. The degree and speed of improvement differ from person to person, and the plan needs a doctor’s in-person assessment. Common approaches include:
- Addressing the underlying cause: if it relates to insulin resistance, weight or hormones, the doctor may suggest weight management, diet and activity changes, and referral to a relevant specialty for follow-up if needed. Weight management supports overall metabolic health, and the skin may improve gradually with it.
- Reviewing medicines: if a medicine is suspected, the doctor will consider whether to adjust it; do not stop any medicine on your own.
- Considering metabolism-related treatment: the doctor may consider whether metabolism-related medicine is needed in your situation, and how and how often to follow up.
- Local skin care: the doctor may consider topical medicine that conditions the keratin layer, moisturizing and protection, and where appropriate gentle peels or lasers as supportive options; these mainly improve appearance, cannot replace addressing the underlying cause, and each has its own suitable candidates and limits.
- Regular follow-up: the appearance changes slowly and may come back, so return for follow-up as the doctor arranges.
If you are thinking about weight management, you can first learn about how weight management is assessed in the clinic; see also the types of diabetes and common causes of fatty liver to understand what metabolic problems may involve.
Whichever approach is used, whether it suits you, how to combine them and for how long should be assessed in person by a doctor, who should explain the possible limits and risks.
What can you do at home? 8 daily care tips for acanthosis nigricans
These habits help reduce friction and irritation and support a healthy lifestyle, and can be adjusted to your situation; if the change is marked or keeps spreading, see a doctor first to confirm.
- Do not scrub hard: scouring with a loofah or bath brush only irritates the skin and may make it darker and rougher.
- Cleanse gently and dry the folds: use gentle cleansers and pat the neck and underarm folds dry afterwards to reduce trapped moisture.
- Moisturize: choose gentle, low-irritation moisturizers to keep the skin barrier healthy.
- Reduce friction: choose soft, breathable, not-too-tight clothes and collars, and avoid necklaces or tight clothing rubbing for long periods.
- Stay active: arrange aerobic and strength activity to suit your condition, which supports how the body responds to insulin; if you have an existing illness or discomfort, talk to your doctor first.
- Adjust your diet: cut down on sugary drinks and refined sweets, eat a balanced mix of vegetables, protein and whole grains, and avoid binge eating.
- Keep a regular routine: lack of sleep and long-term stress may affect appetite and metabolism, so keep regular sleep.
- Record and follow up: take photos of the affected area and note weight changes (for your own comparison) to show the doctor at follow-up.
Using whitening or exfoliating products of unknown content on your own is not recommended, nor is long-term use of strong products to “whiten” the skin, to avoid irritating it or delaying the search for the underlying cause.
Common myths about acanthosis nigricans
Myth 1: A dark neck is just not washed clean, and scrubbing hard will make it lighter?
No. Acanthosis nigricans is thickening and extra pigment in the skin itself, not dirt; scrubbing hard only inflames and roughens the skin, may make it darker, and cannot deal with the underlying insulin or hormone status.
Myth 2: Only people who are overweight get acanthosis nigricans?
Not necessarily. Weight gain is a common related factor, but family tendency, polycystic ovary syndrome, other hormone problems or certain medicines can also cause it, so people who are not overweight should have it assessed by a doctor too.
Myth 3: Having acanthosis nigricans means you already have diabetes?
Not necessarily. It may signal that insulin resistance or metabolic status needs attention, but it does not mean diabetes has been diagnosed; whether blood sugar and other tests are needed should be decided by a doctor based on your situation.
Myth 4: Whitening products will fix it?
Whitening products cannot deal with the underlying cause, and long-term use of products of unknown content may irritate the skin. It is best to have a doctor confirm the diagnosis and underlying cause first, and then decide whether to add local treatment.
When should you see a doctor?
If darkening or thickening of the neck or underarms persists, it is best to have a dermatologist confirm whether it is acanthosis nigricans. Please see a doctor for assessment as soon as possible if:
- Darkening and thickening of the neck or underarms persists, will not wash off and does not improve.
- It spreads quickly over a short time, covers a wide area, or reaches the lips, palms, backs of the hands or other areas.
- It comes with marked itching, unusually thick skin, odor or signs of infection.
- Weight drops noticeably without deliberate effort, or appetite worsens or you tire easily.
- You are often thirsty, pass urine frequently, have blurred vision, or have a family history of diabetes.
- A woman has irregular periods, marked acne or excess hair.
- A child or teenager has acanthosis nigricans; a doctor should assess whether further follow-up is needed.
To confirm why your skin has changed, visit Ruian Clinic Dermatology for an in-person assessment, and read more skin and metabolism topics in the health library.
Health Education References
- Taipei City Hospital Yangming Branch: patient education on acanthosis nigricans
- DermNet: Acanthosis nigricans
- Primary Care Dermatology Society (PCDS, UK): Acanthosis nigricans
No. It is a change in the skin itself and has nothing to do with contact or sharing items, so it does not spread to other people. If you are unsure why the neck or underarms have darkened, have a dermatologist examine you in person.
Not necessarily. A dark neck may also come from friction, dirt, tinea versicolor, pigmentation after contact dermatitis or other skin problems. Acanthosis nigricans is typically grey-brown to dark, thick and velvety, and found in folds; the actual judgment needs an in-person exam by a doctor.
Not necessarily. In most cases the doctor can judge from the appearance, and whether blood tests are needed depends on weight changes, family history, periods, medicines and how fast it is changing. If there are related risk factors, the doctor may suggest tests of blood sugar, blood lipids or hormones.
The focus is finding the underlying cause, such as weight, insulin resistance or hormone problems, and adding local skin care where needed. The degree and time of improvement vary from person to person and it may come back, so have a doctor assess it and follow up regularly.
Long-term use of whitening or exfoliating products of unknown content is not recommended; they may irritate the skin and cannot deal with the underlying cause. Have a doctor confirm the diagnosis first, then discuss whether and how to add local treatment.
A dark, thickened neck or underarm in a child or teenager may also be acanthosis nigricans. A doctor should assess whether it relates to weight, insulin or family tendency and decide whether follow-up is needed. Do not let the child scrub hard, and do not use products of unknown content on your own.
Doctor’s note: dark skin on the neck and underarms is not only a skin issue—confirm the cause before deciding how to manage it
Dark, rough skin on the neck or underarms may be acanthosis nigricans, but it may also be friction, tinea versicolor, pigmentation after contact dermatitis or another skin problem, each managed differently. At your visit, mention how long the skin has been dark, whether it is spreading, recent weight changes, whether diabetes runs in the family, whether periods are regular, and which medicines and supplements you take, so the doctor can examine and assess. Please avoid hard scrubbing or long-term use of whitening products of unknown content; whether tests or treatment are needed, which type and for how long should be assessed by a doctor in person.
This article is health education about a medical condition. It is not a drug advertisement and does not recommend or sell any specific medicine. It cannot replace a doctor’s consultation; diagnosis, tests and treatment must be assessed in person by a doctor based on your individual situation.
Dermatology medical team
Dr. Tseng
