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Skincare Intelligence

Under-eye circles, skin-fold darkening and friction marks

Why under-eyes, skin folds, thighs and lips can darken, what a routine can't fix, and when darker, velvety skin in folds is worth a doctor's check.

Education, not a diagnosis. Only a clinician who examines your skin can say what you have. Every point below shows how strong the evidence is and links to its source.

Who it affects

  • Under-eye darkness affects people of every skin tone and has many causes: inherited pigment, marks left by eczema or allergy, puffiness, visible blood vessels, and shadows from volume loss or loose skin.[1]Thin
  • Velvety, thickened dark skin in body folds (acanthosis nigricans) is reported more often in Native American, Black and Hispanic people in US clinical references, and anyone can be affected.[2,3]Supported
  • Friction darkening can happen to anyone whose skin is rubbed again and again.[4]Thin
  • Darker lips can be normal inherited pigment. Lip darkening can also come from inflammation, hormones, medicines or, rarely, growths.[5]Thin

What it can look like

  • Under-eye darkness can come from pigment, blood vessels or shadowing, and these can overlap.[1,6]Thin
  • Acanthosis nigricans is dark, thickened, velvety skin, often in the neck, armpits or groin.[2,3]Supported
  • Friction darkening shows up where skin is rubbed, such as the inner thighs and over bony areas. Unlike acanthosis nigricans, it is not usually velvety or thickened.[4]Thin

What helps

Under-eyes: match the approach to the cause

  • The cause should be worked out before choosing a treatment.[1]Thin
  • In a systematic review of 39 studies, what helped depended on the cause: fillers or fat for volume loss, surgery for loose skin, and creams or peels for pigment. High-quality evidence was limited.[6]Thin
  • A pigment-fading cream will not change shadows or visible blood vessels.[1,6]Thin
  • Calming eczema or allergy around the eyes, and not rubbing them, addresses one common cause of under-eye pigment.[1]Thin
  • Daily sun protection helps keep pigment from darkening further.[7,8]Mechanistic only

Velvety or thickened skin in folds

This one is a health question before it is a skincare question.

  • Acanthosis nigricans is commonly linked to insulin resistance, prediabetes, type 2 diabetes and obesity. It can also relate to hormonal conditions or medicines.[2,3]Established
  • The American Academy of Dermatology describes it as a possible warning sign that needs medical attention. It is not just cosmetic.[3]Mechanistic only
  • A doctor's check typically includes screening for diabetes.[2]Supported
  • Rarely, it is linked to internal cancer. Rapid onset in middle-aged or older adults is a reason for a prompt check.[2,3]Supported
  • A fading routine is not the answer here. The first step is finding out what is behind it.[2,3]Mechanistic only

Friction marks

  • The first step is removing the friction: looser clothing, less rubbing between the thighs, and no scrubbing with nylon loofahs or brushes.[4]Thin
  • Treatments for underarm darkening had variable results in small, mixed studies, so there is no standard approach.[9]Thin
  • Irritation from products can also leave dark marks, so gentle care matters in folds too.[10,11]Supported

Lips

  • Lip darkening has a wide range of causes, and most of what is known comes from case reports and small studies.[5]Thin
  • Inflammation, such as an allergy to something that touches the lips, is one possible cause.[5]Thin
  • A single new or changing dark spot on the lip is different from overall darkening and needs a prompt check.[5,12]Mechanistic only

What to avoid

  • Building a fading routine for velvety, thickened fold darkening instead of seeing a doctor.[2,3]Mechanistic only
  • Scrubbing folds, thighs or underarms with loofahs or brushes.[4]Thin
  • Rubbing your eyes.[1]Thin
  • Expecting a pigment cream to fix hollows, puffiness or visible vessels under the eyes.[1,6]Thin
  • Using bleach or unregulated lightening creams on folds, lips or under the eyes.[7,13]Mechanistic only

When to see a clinician

  • Skin in the neck, armpits, groin or other folds becomes darker, thicker and velvety.[3]Mechanistic only
  • That change came on suddenly or is spreading widely, especially in middle age or later. Get it checked soon.[2]Supported
  • A single dark spot on the lip, or anywhere else, is new, changing or irregular. Get it checked promptly.[5,12]Mechanistic only
  • Under-eye darkness comes with ongoing itching, swelling or rash.[1]Thin
  • Lip darkening started after a new medicine.[5]Thin

Label claims to question

“Brightening (for under-eyes)”
A cosmetic claim, not a regulated term. It cannot change shadows or visible vessels, and it does not show the product fades pigment.[1,13]
“Clinically proven”
Under-eye and lip studies are mostly small or case reports, and results depend on the cause. Without the study details, the phrase tells you little.[5,6]

Where the evidence is thin

  • Under-eye and lip darkening evidence is mostly case reports and small, mixed studies. Treatments cannot be reliably ranked.
  • Marketing claims for under-eye and lip lightening are largely unsupported by the evidence reviewed.
  • How likely any one person with fold darkening is to have an underlying condition is not known from these sources.
  • Evidence for treating underarm darkening is small and mixed.
  • The review on friction darkening could not be fully identified (authors and year were not captured), though its content was checked.

Keep going

Sources

Retrieved and read for this guide; reviewed 2026-09-13. A source listed here says what it establishes and what it does not — a citation is not an endorsement.

  1. [1]Periorbital Hyperpigmentation: A Comprehensive Review · J Clin Aesthet Dermatol (PMID 26962392), 2016 · read at abstract levelEstablishes: Under-eye darkness has many causes: heredity, PIH (for example from atopic or allergic contact dermatitis), swelling, visible blood vessels, laxity, shadowing and ageing. Identifying the underlying cause guides management.Does not establish: That any topical works for all types, or population prevalence.
  2. [2]Acanthosis Nigricans (StatPearls) · NCBI Bookshelf (Hughes, Brady, Rawla), 2023Establishes: Acanthosis nigricans is more prevalent in Native American, African American and Hispanic people. Most commonly linked to insulin resistance and obesity; also endocrine disorders and drugs. Rapid onset in middle-aged or older adults raises concern for malignancy. Evaluation includes diabetes screening.Does not establish: The probability of malignancy.
  3. [3]Acanthosis nigricans: Overview · American Academy of Dermatology, 2026Establishes: Acanthosis nigricans is dark, thickened, velvety skin, often in body folds. It is linked to insulin resistance, prediabetes and type 2 diabetes, obesity, hormonal conditions and medicines, and rarely internal cancer. It can be a warning sign that needs medical attention, and scrubbing will not remove it.Does not establish: How likely any one person is to have an underlying condition, or any data by skin tone. It does not describe darkening from friction or shaving.
  4. [4]Current understanding of frictional dermatoses: A review · Indian J Dermatol Venereol Leprol, 2026Establishes: Frictional melanosis comes from repeated rubbing (nylon loofahs or brushes, tight clothing, thighs rubbing together) over bony areas, inner thighs and similar sites. Management is to remove the friction first. It differs from acanthosis nigricans, which is thickened and velvety and linked to metabolic disease.Does not establish: Controlled treatment data — it gives none.
  5. [5]Approaches to the evaluation of lip hyperpigmentation · Int J Dermatol, 2012 · read at abstract levelEstablishes: Lip darkening has physiologic or genetic, inflammatory, endocrine, drug-related and neoplastic causes. The evidence is largely case reports and small series.Does not establish: Prevalence by skin tone, or treatment efficacy.
  6. [6]Treatments of Periorbital Hyperpigmentation: A Systematic Review · Dermatol Surg, 2021 · read at abstract levelEstablishes: Across 39 studies, the best treatment depended on cause: fillers or fat for volume loss, surgery for laxity, topicals or peels for pigment. Lasers gave mild-to-moderate benefit. High-quality evidence is limited.Does not establish: A reliable ranking of treatments.
  7. [7]How to fade dark spots in darker skin tones · American Academy of Dermatology, 2025Establishes: Advises tinted broad-spectrum SPF30+ sunscreen with iron oxide and treating the underlying cause. Lists azelaic, glycolic and kojic acids, retinoids and vitamin C as ingredients. Says to avoid irritating products, liquid bleach, and imported products with unlisted steroids or mercury. Fading takes 6–12 months for lighter spots and can take years for deeper ones.Does not establish: Any ranking of the ingredients, or trial evidence for them. Not individual advice.
  8. [8]Postinflammatory Hyperpigmentation (StatPearls) · NCBI Bookshelf (Lawrence, Syed, Al Aboud), 2024Establishes: PIH is more common in Fitzpatrick IV–VI; up to 65% in darker-skinned acne patients. Triggers include acne, dermatitis, infections, lasers, peels, cryotherapy and burns. Epidermal PIH resolves in about 6–12 months; dermal PIH is slow and may be permanent. Prevention: sunscreen, gentle care, not picking, treating inflammation early. Combination therapy is described as most effective.Does not establish: Systematic grading — it is not a systematic review. Does not discuss niacinamide or tranexamic acid.
  9. [9]Axillary Hyperpigmentation Treatment: A Systematic Review · J Cosmet Dermatol, 2025 · read at abstract levelEstablishes: For underarm darkening, topicals (niacinamide, desonide, herbal) showed variable efficacy. Q-switched Nd:YAG was effective in 3 studies.Does not establish: A standard approach — studies are small and mixed.
  10. [10]Postinflammatory hyperpigmentation · DermNet (NZ), 2015Establishes: PIH is more intense and longer-lasting in darker skin. Inflammation drives melanin production, with an epidermal form and a dermal (macrophage) form. Physical treatments can worsen PIH by injuring the epidermis.Does not establish: Any trial data or comparative efficacy — it gives none. The page was last updated in December 2015.
  11. [11]Postinflammatory hyperpigmentation: a review of the epidemiology, clinical features, and treatment options in skin of color · J Clin Aesthet Dermatol 3(7):20–31, 2010Establishes: PIH is more frequent and more severe in darker skin. Cites a 2002 acne study reporting PIH in 65.3% of African-American, 52.7% of Hispanic and 47.4% of Asian acne patients. Explains epidermal vs dermal PIH. First-line care is treating the underlying inflammation plus photoprotection and depigmenting agents; treatment irritation can worsen PIH. Agents covered: hydroquinone 2–4% (ochronosis risk with prolonged use), azelaic acid 20%, retinoids (irritation in up to about 50%), niacinamide, kojic acid (contact dermatitis common), vitamin C. Glycolic and salicylic peels need care. Longer laser wavelengths are described as lower-risk.Does not establish: Graded evidence — it is a narrative review, 16 years old. The survey figures are secondary citations; the primary study was not fetched.
  12. [12]Finding skin cancer in darker skin tones · American Academy of Dermatology, 2025Establishes: People with darker skin need sun protection too. Skin cancer in darker skin is often advanced by the time it is diagnosed. Advises tinted iron-oxide SPF30+ broad-spectrum water-resistant sunscreen.Does not establish: Prevalence figures for pigmentation.
  13. [13]FDA Warns Consumers of Skin Products Containing Mercury and/or Hydroquinone · US Food and Drug Administration (Health Fraud), 2026Establishes: FDA testing since 2019 found some lighteners with mercury at 47 to 27,762 ppm and/or hydroquinone. The products were marketed as whitening, bleaching or brightening, came from several countries, and were sold on large online marketplaces. Kidney, nerve and skin harms are listed. Repeats that there are no legal OTC lighteners in the US.Does not establish: Steroid adulteration, which it does not cover. It does not show that every product using the word 'brightening' contains these ingredients.
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