The short answer
Dark, velvety skin on the back or sides of the neck is called acanthosis nigricans. It is not dirt and will not scrub off. The discoloration results from excess insulin in your bloodstream triggering skin cell overgrowth and increased melanin production.
In most people it is a sign that the body is making extra insulin to keep blood sugar normal, a stage called insulin resistance. It often lightens over months once the cause is treated. A simple blood test is the right next step. If the darkening appeared suddenly, is spreading quickly, or you have lost weight without trying, see a doctor promptly.
Quick check: what should I do?
Pick the description closest to you. This is a guide, not a diagnosis.
Book a routine check
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Darkening came on slowly, over months or years
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Only neck, armpits or groin
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No other symptoms
Next step: arrange a blood test and assessment in the coming weeks.
Book a routine check
Book this week
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Patches plus thirst, passing urine often or blurred vision
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Irregular periods, acne or excess hair (possible PCOS)
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Family history of diabetes, or a past high sugar reading
Next step: book an assessment within the week.
Book this week
See a doctor promptly
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Darkening appeared suddenly or is spreading fast
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Palms, lips or inside the mouth affected
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Unexplained weight loss or feeling unwell
Next step: see your GP or call us within days. Vomiting, confusion or extreme drowsiness with very high sugar: go to A&E or call 995.
Call 6334 2301Quick check: what should I do?
Pick the description closest to you. This is a guide, not a diagnosis.
Book this week
-
Patches plus thirst, passing urine often or blurred vision
-
Irregular periods, acne or excess hair (possible PCOS)
-
Family history of diabetes, or a past high sugar reading
Next step: book an assessment within the week.
Book this week
See a doctor promptly
-
Darkening appeared suddenly or is spreading fast
-
Palms, lips or inside the mouth affected
-
Unexplained weight loss or feeling unwell
Next step: see your GP or call us within days. Vomiting, confusion or extreme drowsiness with very high sugar: go to A&E or call 995.
Call 6334 2301Not sure which applies? Ask us first.
We reply within [PLACEHOLDER: hours] during clinic hours · GP referral [PLACEHOLDER: not required / required] · Your details stay private
What is acanthosis nigricans?
Acanthosis nigricans is a change in the skin, not a disease on its own. Patches look darker, feel thicker and velvety, and usually sit in skin folds. It develops gradually over months or years and is usually painless and not itchy.
How it looks
Light brown to almost black, depending on your skin tone and the severity of insulin resistance. Clear borders with an irregular, map-like edge.
How it feels
Softer and thicker than nearby skin, like velvet or suede. Skin lines look deeper. Small skin tags may appear in the same area.
How it spreads
The back of the neck usually darkens first, then the sides. In more marked cases it can circle the whole neck.
Where it shows up
- Back and sides of the neck — usually the first and most visible site
- Armpits, sometimes extending onto the upper arms
- Groin and inner thighs
- Knuckles, under the breasts and along the belt line
Beyond the neck, insulin resistance can cause similar changes in other body areas.
Unusual sites: palms, lips or inside the mouth. Get these checked promptly.
Why the neck? Skin folds trap warmth, moisture and friction, and skin there responds strongly to high insulin levels, so changes show up early and clearly.
Where it shows up
- Back and sides of the neck — usually the first and most visible site
- Armpits, sometimes extending onto the upper arms
- Groin and inner thighs
- Knuckles, under the breasts and along the belt line
Beyond the neck, insulin resistance can cause similar changes in other body areas.
Unusual sites: palms, lips or inside the mouth. Get these checked promptly.
Why the neck? Skin folds trap warmth, moisture and friction, and skin there responds strongly to high insulin levels, so changes show up early and clearly.
How Insulin Resistance Develops
Insulin helps muscle, fat and liver cells take up sugar from the blood. When those cells stop responding well, the body compensates by making more insulin, and that extra insulin is what the skin reacts to.
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STEP 1
Cells respond poorly to insulin
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STEP 2
The pancreas makes more insulin to compensate
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STEP 3
Insulin stays high in the blood (hyperinsulinemia)
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STEP 4
Skin cells in folds grow faster and darken
What Pushes Insulin Resistance Along
Waist fat
Fat around the abdomen releases substances that interfere with insulin signalling.
Inactivity
Working muscles take up sugar; less movement means less uptake.
Genes & family history
Some people are more susceptible; Asians tend to develop it at a lower body weight.
Eating pattern
Frequent refined carbohydrates and sugary drinks, and too little fibre.
Poor sleep & stress
Both raise cortisol, which works against insulin.
Medicines & PCOS
Corticosteroids, some antipsychotics, and PCOS can all play a part.
Did you know? Insulin resistance can be present for years before blood sugar rises into the diabetes range. Skin changes often appear in this earlier stage, which makes them a useful prompt to get tested.
Video: Recognising the early warning signs of insulin resistance · Arden Endocrinology
How quickly it appeared
Timing is one of the most useful clues. Insulin-related darkening usually builds slowly.
| What you noticed | What it usually means | What to do |
|---|---|---|
| Gradually, over months or years | Most often linked to insulin resistance, prediabetes, type 2 diabetes, PCOS or weight gain. | Routine: blood test and assessment in the coming weeks. |
| Over a few weeks, with other symptoms | Could mean blood sugar is already raised, or a hormonal or medicine-related cause. | This week: book an assessment; bring your medicine list. |
| Suddenly, spreading, or at unusual sites | Uncommon. Rarely, a form linked to an internal illness that needs prompt checks. | Promptly: see a doctor within days. |
Causes
High insulin levels stimulate skin cells in body folds to grow faster and darker. Common reasons insulin runs high:
Insulin resistance
The most common cause. Often reversible with early action.
Diabetes
Patches may appear before or after diagnosis.
PCOS
Insulin resistance is common with polycystic ovary syndrome.
Metabolic syndrome
Waist fat, blood pressure and lipids often travel together.
Medicines
e.g. steroids, high-dose niacin, some hormone treatments. Never stop a medicine without advice.
Other causes
Other hormone disorders, inherited forms, or a cancer-associated type (sudden onset).
Why it matters
High insulin levels stimulate skin cells in body folds to grow faster and darker. Common reasons insulin runs high:
Early warning
The patches can appear years before blood sugar reaches the diabetes range, which makes them a useful early prompt.
Hormones and PCOS
Irregular periods, acne or excess hair alongside the patches suggest checking both hormones and insulin.
Weight and stigma
Worth assessing early, without blame.
Medicines list
Bring a full list, including supplements. Your doctor decides whether anything should change.
How it’s treated
Treatment targets the underlying metabolic dysfunction. When insulin sensitivity improves, the skin usually lightens on its own, more slowly than the blood results.
1. Eating & movement
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Fewer refined carbohydrates; vegetables and protein before rice or noodles
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A Mediterranean-style diet pattern
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Aerobic and resistance exercise, plus short walks after meals
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Gradual, sustainable weight loss
2. Medicines, when needed
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Metformin to improve insulin sensitivity
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GLP-1 medicines with weight management in Singapore, for suitable patients
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All prescription-only; your doctor weighs benefits and side effects
3. Caring for the skin
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Gentle cleansing; moisturisers with urea or lactic acid
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Prescription retinoid creams can help appearance
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Peels or laser are dermatology treatments; we can refer
While you wait
Use the sign in the right-hand column, not just the calendar. Ranges assume a straightforward fistulotomy.
Do
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Wash gently and moisturise; the skin is not dirty
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Note when it started and take a photo every few weeks
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List your medicines and supplements to bring along
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Try a 10-minute walk after main meals
Avoid
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Straining or delaying the urge to go
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Scented or alcohol wet wipes on the wound
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Sitting for long periods directly on the wound
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Heavy lifting and strenuous exercise
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Driving for 24 hours after anaesthesia
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Alcohol while on prescribed pain relief
About treatments you may read about: retinoid creams (such as tretinoin), metformin and GLP-1 medicines are prescription-only and not right for everyone. Tretinoin is avoided in pregnancy. Please discuss them with your doctor before use.
What improvement looks like
Blood results usually improve before the skin does. Skin changes can take several months to fade.
- Blood markers improving at your review
- Waist measurement coming down
- Skin feels softer, less velvety
- Colour gradually lighter in photos
- No new areas appearing
- Follow-up every 3–6 months
Your consultation
Tick all five before going back to the gym, running or heavy work.
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1
Message or call
When it started, symptoms, family history, medicines.
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2
History and examination
Usually HbA1c, fasting glucose and lipids; others if needed.
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3
Tests if needed
What the numbers mean and a plan you can follow.
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4
A written plan
Review of progress and adjustments over time.
Referral
[PLACEHOLDER: self-referral accepted? GP letter needed for insurance?]
Insurance
[PLACEHOLDER: panels, Letter of Guarantee, MediSave eligibility] · Insurance information
Consult fee
First consultation [PLACEHOLDER: S$ range, before GST]; tests charged separately.
Book an assessment
Seeing an endocrinologist in Singapore means a full metabolic check, not just a skin review. Message, call or send the short form below and we’ll confirm a time that suits you.
Arden Endocrinology Specialist Clinic, Mount Elizabeth Novena
Mount Elizabeth Novena Specialist Centre, #04-28
38 Irrawaddy Road, Singapore 329563
Mon – Fri: 8.30am – 12.00pm, 2.00pm – 4.30pm
Sat: 8.30am – 11.30am
Sunday and public holidays: Closed
Frequently Asked Questions
The patches themselves are harmless. What matters is the cause behind them, most often insulin resistance, which raises the risk of type 2 diabetes. Rarely, sudden or fast-spreading darkening points to another illness, so that pattern should be checked promptly.
Yes. When the underlying insulin resistance is treated, the patches usually lighten gradually over months. The velvety texture often improves first, while colour can take longer to fade.
Yes. It often appears during insulin resistance years before blood sugar reaches the diabetes range. It can also occur with PCOS, some medicines, thyroid or other hormone conditions, and rarely with an internal illness.
PCOS and insulin resistance often occur together. Higher insulin levels can increase androgen production, which worsens acne, excess hair and irregular periods. Checking both hormones and insulin helps guide treatment.
The most common cause is high insulin levels from insulin resistance, prediabetes, type 2 diabetes or weight gain. Other causes include PCOS, corticosteroids and some other medicines, thyroid or other hormone disorders, and rarely a cancer-associated form.
Treat the underlying cause first: improve insulin sensitivity with diet, activity, weight management and, where appropriate, medicines such as metformin or GLP-1 therapy. Skin-directed options include gentle moisturisers with urea or lactic acid, prescription retinoid creams, and dermatology treatments such as peels or laser.
See a doctor promptly if the darkening appears suddenly, spreads quickly, affects the palms, lips or inside the mouth, or comes with unexplained weight loss or feeling unwell. Slow, stable patches in skin folds are usually related to insulin resistance and should still be checked.
Start with an endocrinologist if the patches appeared with weight change, thirst, frequent urination, irregular periods or a family history of diabetes. We check the metabolic cause and can refer you to a dermatologist for skin-directed treatment if needed.
Yes. Children and teenagers with excess weight, a family history of diabetes or PCOS can develop acanthosis nigricans. It is worth checking their blood sugar and insulin-related markers early.
References
- American Academy of Dermatology. Acanthosis nigricans: signs and symptoms.
- NHG Health. Acanthosis nigricans.
- Higgins SP, Freemark M, Prose NS. Acanthosis nigricans: a practical approach to evaluation and management. Dermatology Online Journal.
- Topical treatments for acanthosis nigricans: a systematic review of randomised controlled trials. Frontiers in Medicine, 2025.
- [PLACEHOLDER: Singapore MOH / ACE clinical guidance on diabetes and prediabetes]
