Acanthosis nigricans
Acanthosis nigricans is the appearance of dark, thickened, velvety patches of skin in the body's folds.
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Medicines commonly prescribed for Acanthosis nigricans
For informational purposes only. Always consult a doctor before using any medicine.
Dosage form: TABLET, 1000 mgActive substance: metforminManufacturer: Pharmconsul S.R.O.Prescription requiredDosage form: TABLET, 1000 mgActive substance: metforminManufacturer: Tarbis Farma S.L.Prescription requiredDosage form: TABLET, 850 mgActive substance: metforminManufacturer: Medochemie Iberia S.A.Prescription required
Acanthosis nigricans is the appearance of dark, thickened, velvety patches of skin in the body's folds. It is not dirt, it is not contagious and it is not really a skin disease at all: it is an external sign of something happening inside, almost always involving insulin. That is why the point here is not creams but finding the cause.
How it looks
- the skin is thickened and feels velvety or rough, with accentuated skin markings;
- colour ranges from light brown to almost black;
- the edges are indistinct, fading into normal skin;
- typical sites: back and sides of the neck, armpits, groin, under the breasts, elbow creases, knuckles;
- sometimes mild itching;
- small skin tags often appear alongside;
- involvement of the mucous membranes is rare and, when present, calls for broader investigation.
Causes
- insulin resistance — the main cause. Excess insulin in the blood stimulates skin cells to grow. It goes together with excess weight, prediabetes and type 2 diabetes;
- polycystic ovary syndrome;
- obesity, even before any glucose abnormality;
- hormonal conditions — hypothyroidism, Cushing's syndrome, acromegaly;
- medicines — corticosteroids, high-dose nicotinic acid, hormonal contraceptives, some antiretrovirals;
- inherited forms, uncommon, appearing in childhood;
- internal cancers — a rare but important cause. If the changes appear rapidly, are extensive, involve the palms, lips or lining of the mouth, and come with weight loss, a malignancy — usually of the digestive tract — must be excluded.
When to see a doctor
- dark velvety patches have appeared in your skin folds — reason enough to check your blood glucose even with no other symptoms;
- the patches are spreading quickly;
- they involve palms, soles, lips or mouth;
- there is weight loss, loss of appetite or digestive symptoms;
- you have intense thirst, pass urine often or tire easily;
- there are irregular periods and increased facial hair;
- the patches appeared after starting a medicine;
- it is a child or adolescent.
How it is investigated
The diagnosis is made by looking: the picture is recognisable and a biopsy is not usually needed. The main work is finding the cause. The usual tests are fasting glucose and HbA1c, sometimes insulin and an insulin resistance index, lipid profile, thyroid function and, if polycystic ovary syndrome is suspected, sex hormones and ultrasound. The doctor will measure weight, waist circumference and blood pressure and review your medication.
If the picture is atypical or has appeared rapidly in an adult, investigation is widened to exclude an internal cancer.
Treatment
The skin responds to what is done about the cause, not the other way round. That is the central message.
- address insulin resistance: weight loss, physical activity, fewer fast-absorbed sugars. With moderate weight loss the patches visibly lighten;
- metformin or other medicines where indicated;
- treatment of polycystic ovary syndrome or the relevant hormonal condition;
- review of the responsible medicine, always by a doctor;
- creams with retinoids, urea or lactic acid: they improve texture and colour but are an adjunct, not the solution;
- laser or chemical peels: cosmetic options once the cause is controlled;
- cancer treatment if that turns out to be the cause; the skin improves once it is treated.
What you can do
- do not scrub the area: it is not dirt, and scrubbing only irritates and can darken the skin further;
- wash with gentle products and moisturise daily;
- loose cotton clothing to reduce friction in the folds;
- if you sweat heavily, dry the folds thoroughly: moisture encourages fungal infections that are mistaken for acanthosis;
- walk every day and cut sugary drinks — these have the biggest effect on the outcome;
- have your glucose checked even if you feel well;
- bring your doctor a full list of medicines and supplements.
Common questions
Is it contagious? No.
Will it go? Once the cause is addressed the skin lightens gradually, over months. In long-standing cases some thickening may remain.
Does it mean I have diabetes? Not necessarily, but it is a reason to check: it is often the first visible sign of insulin resistance.
Do skin-lightening creams help? No, and they can irritate the skin.
Why has a slim teenager developed it? Insulin resistance can occur without obesity, and inherited forms exist. It is worth investigating.
Online consultation
In an online consultation the doctor reviews photographs, advises which tests will show insulin resistance, reviews your medication, recognises the features that call for wider investigation and helps you build a concrete plan to improve the skin by treating the cause.
This material is for information only and does not replace a medical consultation.
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Reviewed on Jul 16, 2026
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