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OverviewAetiologyPathophysiologyClinical features and red flagsInvestigationsDifferential diagnosisManagementComplicationsMonitoring and follow-upSpecial situationsCommon pitfallsQuestionsSources
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Educational draft · awaiting clinical reviewThe full textbook explains uncertainty but does not replace live national or local guidance, specialist advice, or current prescribing information.

Acanthosis nigricans

Dermatology · UK scope · Sources checked 27 Aug 2026 · Clinical review pending

RapidFull

Overview

Recognise the velvety flexural phenotype, investigate common metabolic and endocrine drivers without stigma, and identify the rare sudden extensive pattern that can signal internal malignancy.

Acanthosis nigricans describes a reaction pattern rather than one disease. The skin becomes thick, soft or papillomatous and grey-brown to dark brown, classically across the back and sides of the neck, axillae, groins and other folds. Skin tags often coexist. Similar colour without texture can reflect friction or post-inflammatory change; palpation and comparison with less affected skin reduce overdiagnosis. The finding can occur at any body size and should trigger a measured history rather than an assumption about behaviour.

High circulating insulin can activate insulin-like growth pathways in keratinocytes and fibroblasts, linking the common phenotype to insulin resistance. Diabetes risk, adiposity, PCOS, family tendency and selected medicines are relevant. Rare paraneoplastic acanthosis is usually abrupt, extensive and symptomatic and may involve mouth or palms. Its rarity argues against indiscriminate cancer imaging in a young person with a stable metabolic pattern, while its clinical severity argues against ignoring a convincing red-flag presentation.

The consultation should address both the medical association and the visible skin. Ask what the person wants changed, offer evidence-based diabetes and cardiovascular risk assessment, and provide practical fold and friction care. Treating insulin resistance improves health whether or not pigmentation clears; cosmetic response must not be used as a surrogate for HbA1c or metabolic success.

Key points

  • Acanthosis nigricans is velvety thickened hyperpigmented skin, usually on the posterior neck, axillae or groins; texture and distribution are more diagnostic than colour alone.
  • Insulin resistance associated with higher adiposity, type 2 diabetes or polycystic ovary syndrome is the commonest acquired context, but the sign is not itself a glucose diagnosis.
  • Examine respectfully in good light and ask permission before folds are exposed; in dark skin the change may be prominent, but baseline pigmentation must not be pathologised.
  • Check blood pressure and metabolic risk, then use HbA1c or glucose testing through the appropriate diabetes pathway rather than assuming normality or disease from appearance.
  • Irregular cycles, hirsutism or fertility concerns support a PCOS assessment, while hypothyroid, Cushing or medicine testing should follow specific clinical clues.
  • Sudden extensive itchy disease, mucosal papillomatosis, tripe palms and unexplained weight loss are uncommon but important malignant-acanthosis features.
  • Treating the driver may soften and lighten skin gradually; weight-management support should be person-centred and never framed as blame or a guaranteed cosmetic cure.
  • Keratolytics and retinoids offer inconsistent cosmetic benefit and can irritate folds, so underlying risk reduction and realistic expectations remain central.

Aetiology

01

Insulin resistance

Hyperinsulinaemia associated with adiposity, type 2 diabetes or PCOS is the commonest acquired driver of the characteristic flexural skin response.

02

Familial or syndromic disease

Stable childhood or adolescent acanthosis can reflect inherited susceptibility or a rarer genetic insulin-resistance syndrome, especially when severe at low adiposity.

03

Medicine-associated change

Systemic glucocorticoids, high-dose nicotinic acid, insulin and selected hormonal medicines may provoke or amplify acanthosis through metabolic or growth signalling.

04

Paraneoplastic signalling

Rare internal tumours release growth factors that produce abrupt extensive acanthosis, often with severe itch, mucosal papillomatosis and palmar thickening.

Pathophysiology

  1. 1
    Growth receptors are activated

    High insulin or tumour-derived growth signals stimulate keratinocyte and dermal fibroblast receptors, increasing epidermal thickness and papillomatosis.

  2. 2
    Skin markings deepen

    Hyperkeratosis and papillomatosis accentuate natural flexural lines and shadowing, while increased pigment contributes variably to the visible colour.

  3. 3
    Friction amplifies texture

    Occlusion and rubbing in folds can thicken an established plaque, although mechanical friction alone does not explain every metabolic or malignant case.

Clinical features and red flags

Velvety neck plaque

Symmetrical thickened skin with accentuated markings over posterior or lateral neck is the commonest readily visible presentation.

Flexural involvement

Axillary, groin, inframammary, elbow or knuckle change and accompanying acrochordons support the reaction pattern when texture is convincing.

Metabolic constellation

Central adiposity, hypertension, dysglycaemia, irregular cycles or hirsutism makes insulin resistance and PCOS clinically relevant without proving either diagnosis.

Medication relationship

Onset after systemic glucocorticoids, high-dose nicotinic acid, insulin or selected hormonal treatment warrants a benefit-risk review with the prescriber.

Malignant-pattern warningRed flag

Rapid widespread itch, mucosal papillomatosis, tripe-like palms and weight loss in an older person demand expedited systemic assessment.

Pseudoacanthosis distinction

Retained keratin or terra-firma-forme dermatosis may wipe away with alcohol, while ordinary dirt should never be assumed from skin colour.

Red flags requiring action

  • Abrupt rapidly progressive acanthosis in an older adult, especially with weight loss, marked itch, mucosal involvement, tripe palms or no metabolic explanation, requires expedited investigation for an internal malignancy.

Investigations

  1. 01
    HbA1c or fasting plasma glucoseFirst step
    Why
    Detect prediabetes or type 2 diabetes in a metabolically plausible phenotype.
    Interpretation and limitations
    Use diagnostic thresholds and repeat confirmation rules from diabetes guidance; an isolated normal result does not erase future risk or justify fasting insulin measurement.
  2. 02
    Blood pressure, lipids and adiposity assessment
    Why
    Measure associated cardiovascular risk and guide preventive treatment.
    Interpretation and limitations
    Use appropriate cuff and person-centred BMI or waist discussion; each risk factor has its own threshold and should not be inferred from neck appearance.
  3. 03
    PCOS-focused assessment
    Why
    Investigate ovulatory and androgen excess when cycles, hair or fertility history supports it.
    Interpretation and limitations
    Exclude pregnancy and selected endocrine mimics before applying PCOS criteria; ultrasound is not automatically necessary and acanthosis alone is insufficient.
  4. 04
    Targeted endocrine tests
    Why
    Evaluate thyroid disease, Cushing syndrome or another hormonal driver when discriminatory features exist.
    Interpretation and limitations
    Select TSH or validated cortisol testing from clinical evidence; random cortisol and broad hormone panels generate misleading incidental results.
  5. 05

Differential diagnosis

01

Frictional hyperpigmentation

Colour follows rubbing or pressure without the characteristic velvety papillomatous surface and may improve when the mechanical driver stops.

02

Terra-firma-forme dermatosis

Brown retained keratin can resist soap yet wipe away with isopropyl alcohol, avoiding unnecessary endocrine investigation when morphology fits.

03

Confluent papillomatosis

Scaly reticulate papules over central trunk coalesce differently from the smooth velvety neck and fold plaques of acanthosis.

04

Epidermal naevus

A longstanding unilateral linear or Blaschkoid papillomatous plaque suggests mosaic epidermal change rather than a systemic insulin-resistance marker.

Management

01Typical metabolic patternMeasure risk without making assumptionsFirst stepStable flexural acanthosis occurs with plausible insulin resistance and no malignant warning features.+
  1. 1Confirm velvety thickening by examination, document onset and family tendency, and ask about cycles, hair change, medicines, sleep and symptoms of hyperglycaemia.
  2. 2Measure blood pressure and arrange HbA1c or fasting glucose plus lipids and other cardiovascular assessment according to age and risk.
  3. 3Offer person-centred nutrition, activity and weight support where wanted, and treat diagnosed diabetes, hypertension, dyslipidaemia or PCOS through their own evidence-based pathways.
02Atypical or suddenExclude serious acquired driversDisease is abrupt, rapidly spreading, intensely itchy, mucosal or associated with weight loss or tripe palms.+
  1. 1Take a full systemic review, medicine and smoking history and examine mouth, palms, nodes, abdomen and other clinically indicated systems.

Complications

01

Undiagnosed dysglycaemia

Failure to assess the common metabolic phenotype can delay type 2 diabetes diagnosis and cardiovascular risk reduction.

02

Missed internal malignancy

Dismissing an abrupt extensive mucosal phenotype as ordinary metabolic disease can postpone diagnosis of an underlying gastrointestinal or other cancer.

03

Fold discomfort

Thickened occluded skin may itch, macerate, smell or become secondarily inflamed, particularly when friction and sweating are substantial.

04

Stigma and treatment injury

Blame, forceful scrubbing and caustic lighteners cause shame, irritant dermatitis and additional post-inflammatory pigmentation without treating the driver.

Monitoring and follow-up

  • Repeat glycaemic assessment at the interval determined by baseline result and diabetes risk rather than waiting for skin to change.
  • Track blood pressure, lipids and diagnosed metabolic conditions independently of pigmentation response.
  • Review menstrual pattern, fertility goals and androgen symptoms when PCOS is suspected or established.
  • Re-examine if acanthosis accelerates, becomes pruritic, reaches mucosa or palms, or is accompanied by unintentional weight loss.
  • Stop cosmetic products that cause burning, fissuring or new post-inflammatory pigmentation in folds.

Special situations

Texture carries the diagnosis

Hyperpigmentation alone is nonspecific; palpable velvety thickening and a characteristic flexural distribution identify acanthosis more reliably.

The sign is not the test

Acanthosis raises the probability of insulin resistance, but HbA1c or glucose establishes dysglycaemia and guides treatment.

Common and serious can coexist

An older adult may have obesity and a malignancy, so abrupt mucosal or palmar progression should not be dismissed as metabolic.

Pigment change lags biology

Improved glycaemia or weight-related health may precede visible softening by months, and some pigmentation persists despite excellent metabolic control.

Respect improves detection

Permission, privacy and neutral language make full fold examination more acceptable and reduce missed extent or a wrongly attributed cause.

Common pitfalls

  1. 01

    Diagnosing diabetes solely from a dark neck without biochemical testing.

  2. 02

    Equating deeply pigmented normal skin or retained keratin with acanthosis nigricans.

  3. 03

    Using stigmatising language or presenting body weight as a moral cause.

  4. 04

    Ordering broad cancer imaging for every stable young patient while missing the genuinely abrupt malignant phenotype.

  5. 05

    Treating colour cosmetically and failing to measure blood pressure, glucose and cardiovascular risk.

  6. 06

    Assuming improved pigmentation proves that diabetes or PCOS has resolved.

Practice

Two practice questions

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Question 1 of 2
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DermatologyOriginal SBA

Sudden tripe palms

A 67-year-old develops rapidly spreading itchy velvety pigmentation, oral papillomatosis, tripe-like palms and unintentional weight loss over three months. What is the safest interpretation?

Choose one answer, then submit
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Sources and review status4 sources · checked 27 Aug 2026 · clinical review pending+
Sources

Sources and review status

National guidance is shown before implementation-dependent detail. Apply principles in context and verify current guidance when a decision affects care. Source check completed 27 Aug 2026; clinical approval remains outstanding.

  • Primary Care Dermatology Society acanthosis nigricansClinical phenotype, associations, malignant warning features and management.
  • NICE NG28 type 2 diabetes recommendationsDiagnosis and management of dysglycaemia associated with insulin resistance.
  • NICE NG246 overweight and obesity recommendationsPerson-centred assessment and non-stigmatising weight-management pathways.
  • NHS type 2 diabetesSymptoms, diagnosis, prevention and long-term risk communication.

Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes

Authoring stateComplete draftClinical stateAwaiting reviewJurisdictionUnited Kingdom
Skin biopsy
Why
Confirm an atypical keratotic or papillomatous eruption when morphology remains uncertain.
Interpretation and limitations
Histology can support the reaction pattern but does not identify its systemic cause, so it cannot replace metabolic and red-flag assessment.
  • 06
    Urgent malignancy evaluation
    Why
    Identify an internal cancer when the sudden extensive paraneoplastic phenotype is present.
    Interpretation and limitations
    Investigation is symptom-, age- and examination-directed through an urgent specialist pathway; a routine tumour-marker panel is not an adequate screen.
  • 2Arrange expedited dermatology and medical assessment, using age- and symptom-directed imaging or endoscopy rather than relying on nonspecific tumour markers.
  • 3Continue investigation even if a metabolic risk factor coexists, because common insulin resistance does not neutralise a strong paraneoplastic phenotype.
    • 03Skin symptom careReduce friction and treatment injuryTexture, itch, odour or appearance causes symptoms or distress after systemic assessment.+
    1. 1Use gentle washing, dry folds carefully and reduce avoidable friction without implying that ordinary hygiene caused the pigmentation.
    2. 2Consider a cautious trial of a low-strength keratolytic or dermatologist-selected topical retinoid, starting infrequently and stopping inflammation.
    3. 3Review photographs and comfort after several months, explaining that treatment of the underlying driver may improve texture without restoring an exact previous colour.