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Post-inflammatory hyperpigmentation (PIH)

Also known as: PIH, post inflammatory hyperpigmentation, post-acne dark marks, pigmentary sequelae

Post-inflammatory hyperpigmentation is acquired darkening that remains after skin inflammation or injury. Increased epidermal melanin appears brown, while pigment released into the dermis can appear grey-brown or blue-grey and usually resolves more slowly.

Evidence status

Moderate

PIH biology and cause-first management are well supported. Topical and procedural studies are heterogeneous, complete clearance is uncommon, and evidence is concentrated in acne-associated PIH rather than every trigger or skin population.

Definition#

Post-inflammatory hyperpigmentation is an acquired increase in skin colour at the site of previous inflammation or injury. It can follow acne, eczema, contact or irritant dermatitis, infection, burns, friction, picking, hair removal or a professional procedure.[1, 4, 5]

PIH can affect every skin type. It is often more noticeable, severe or persistent in skin with greater constitutive pigmentation, which is one reason the treatment evidence must be read with attention to who was included.[3, 4]

How PIH develops#

Inflammation changes signalling between keratinocytes, immune cells and melanocytes. In the epidermis, that environment can increase melanin production and transfer to keratinocytes. If inflammation disrupts the basal layer, pigment can escape into the dermis, where macrophages ingest it and become melanophages.

This creates two overlapping patterns:

  • Predominantly epidermal PIH: usually tan, brown or dark brown, with pigment in the epidermis. It is generally more accessible to topical and turnover-based approaches.
  • Predominantly dermal PIH: often grey-brown or blue-grey, with pigment held in dermal melanophages. It usually clears more slowly and responds less predictably.[1, 4]

Depth is a clinical estimate, not something that can be read with certainty from one colour under treatment-room lighting.

Common triggers#

PIH can follow almost any process that inflames or injures skin. Common aesthetic-practice contexts include:

  • acne and folliculitis;
  • ingrown hairs, picking and extraction trauma;
  • eczema, irritant dermatitis and allergic contact dermatitis;
  • friction, shaving, waxing and depilatory irritation;
  • burns and infections;
  • peels, microneedling, laser, IPL or other procedures that cause excessive or prolonged inflammation.

The initiating condition changes the plan. Acne-associated PIH cannot be managed well if new inflammatory lesions continue. Underarm darkening caused by repeated hair-removal irritation requires a different first step from facial pigment that appeared after eczema. The umbrella term does not make the causes interchangeable.

PIH versus PIE#

Post-inflammatory erythema is the persistent vascular change that can remain after an inflammatory lesion, particularly acne.[7, 8]i

FeaturePIHPIE
Main visible componentMelaninVascular erythema
Common colourTan, brown, dark brown, grey-brown or blue-greyPink, red or purple
Blanching with pressureUsually little changeMay temporarily fade
More conspicuous inOften darker skinOften lighter skin, but can occur in any skin
Treatment logicControl inflammation; pigment-appropriate topicals or selected proceduresControl inflammation; vascular assessment and selected vascular approaches

This is a reasoning aid, not a diagnostic test. Background skin colour, lighting, residual active acne and mixed pigment-plus-erythema can make colour and blanching difficult to interpret. A mark can contain both. Dermoscopy or medical assessment may be needed when the distinction changes the proposed treatment.

Professional assessment considerations#

A PIH consultation should answer five questions before it discusses correction:

  1. What was the trigger? Was there a clear inflammatory lesion, rash, injury or procedure in the same site?
  2. Is the trigger still active? Look for acne, dermatitis, friction, infection, picking or product irritation.
  3. Is the mark pigment, erythema or mixed? Assess colour, blanching, surface change and the timeline without pretending any one clue is definitive.
  4. How deep might the pigment be? Brown suggests a stronger epidermal component; grey-brown or blue-grey raises the possibility of dermal pigment.
  5. Is PIH a safe assumption? New, changing, irregular, raised, bleeding, itchy, painful or unexplained lesions need medical assessment.[1, 13]

Also record previous PIH, hypopigmentation or scarring; current medication; pregnancy where relevant to products; sun and visible-light exposure; recent procedures; home routines; and the client’s expectations. Fitzpatrick phototype adds context, but does not replace this history.

Prevent new pigment before treating old pigment#

The most reliable management principle is cause first. International consensus places control of the underlying condition at the centre of the PIH algorithm.[1, 4]

That may mean:

  • stabilising acne rather than repeatedly treating each residual mark;
  • removing a sensitising or irritating product;
  • changing a hair-removal or picking behaviour;
  • reducing friction;
  • restoring tolerance before introducing pigment-directed actives;
  • using appropriate photoprotection to reduce darkening and support treatment.

MSTA’s underarm hyperpigmentation guide shows this sequence in practice: distinguish hair shadow and follicular marks from diffuse PIH, remove the trigger, settle inflammation, then reassess remaining pigment.

Relevant topical and medical approaches#

Systematic reviews find evidence across retinoids, hydroxy acids, sunscreen and several other topical strategies, but the studies differ in trigger, skin population, formulation, duration and outcome measure.[2, 3, 9]The correct conclusion is that some topicals improve PIH — not that one universal ranking applies to every mark.

For professional reasoning, useful categories include:

  • Photoprotection: helps prevent UV- and light-associated darkening and supports other management.
  • Inflammation and trigger control: prevents new pigment at its source.
  • Melanogenesis-modulating actives: may reduce new pigment production where the finished product and condition have supporting evidence.
  • Retinoids and controlled turnover: can improve epidermal PIH but can also irritate; tolerance is part of efficacy.
  • Hydroxy acids: have evidence in some PIH studies, but stronger or more frequent is not automatically better.

Hydroquinone requires especially precise language. In the UK it is prohibited as an ingredient in cosmetic products in Great Britain. Where a medicinal route is lawful it must be managed by an appropriately authorised prescriberworking within their competence — a wider category than “a doctor” — and it needs supervision, because irritation and paradoxical darkening are recognised risks. Northern Ireland follows a separate cosmetics regime and should be checked separately.[11, 12]“Hydroquinone is illegal in the UK” is too broad; “it is an ordinary professional cosmetic active” is also wrong.

Relevant professional treatments#

Chemical peels, lasers and light-based treatments can improve selected PIH, especially when the diagnosis, pigment depth, device or formulation and practitioner expertise align. They also create inflammation, which means they can worsen the condition they are intended to treat.

A 2024 systematic review of 41 studies covering 877 patients found complete clearance to be uncommon: 18.1% with laser and energy-based devices, 5.4% with topicals and 2.4% with combination therapy.[2] In the same review, PIH worsened in 2.6% of patients treated with laser and energy-based devices.[1, 2, 3, 10] Most included studies concerned acne-related PIH, limiting generalisation to every cause.

The professional decision is therefore not “which treatment hits pigment hardest?” It is:

  • Is the trigger controlled?
  • Is the pigment likely epidermal, dermal or mixed?
  • Does evidence exist for this indication and skin population?
  • Can the procedure be delivered within scope and with an appropriate test process?
  • Would a slower, tolerable plan carry less risk than another inflammatory event?

Where treatment is appropriate, use the relevant canonical MSTA guide for procedure detail: this entry explains the condition, and does not duplicate the full chemical peels guide or IPL guide.

Contraindications and cautions#

Pause aesthetic PIH treatment when:

  • there is no convincing inflammatory or injury-related history;
  • a lesion is changing, irregular, raised, bleeding, crusted, painful or itchy;
  • active infection, dermatitis, acne excoriée or barrier impairment is present;
  • pigment appeared or worsened after an earlier procedure and the mechanism is unclear;
  • the proposed treatment is outside the practitioner’s scope;
  • the client expects guaranteed clearance or a fixed deadline;
  • a prescription medicine is being presented as a cosmetic product.

Treat active inflammation before escalating pigment correction. Refer when the diagnosis, medical cause or safe scope is uncertain.

What the evidence currently supports#

The evidence supports PIH as an inflammatory pigment sequela with epidermal and dermal patterns. Consensus supports treating the underlying trigger and including photoprotection.

Topical treatments can improve PIH, with the most substantial study support among reviewed options for retinoids, hydroxy acids and sunscreen. However, systematic reviews also show heterogeneous methods, low complete-clearance rates and a strong bias towards acne-related PIH.

Procedures are not excluded, but their evidence and risk vary. The same inflammatory capacity that allows remodelling or pigment removal can create new PIH.

What remains uncertain#

  • The exact contribution of each inflammatory mediator in an individual episode of PIH.
  • A reliable universal method for estimating pigment depth without specialist assessment.
  • A universal clearance timeline. The often-cited long persistence data come from a selected Asian acne-clinic population.[2, 4, 6]i
  • Which intervention is best across different triggers and skin populations; study outcomes are too heterogeneous for one league table.
  • The best way to treat mixed PIE and PIH.
  • Long-term recurrence and maintenance outcomes after many procedures.

Common misconceptions#

“Every post-acne mark is PIH.”

No. Pink, red or purple marks may be vascular PIE, and a mark may be mixed.[7, 8]i

“Darker colour means the pigment is deeper.”

Not necessarily. Hue can suggest a pattern, but lighting, background colour and mixed inflammation complicate the assessment.

“PIH always clears in a set number of weeks.”

No universal deadline is supported. Trigger, depth, skin response, new inflammation and light exposure all matter.[2, 4, 6]i

“A stronger peel or laser clears PIH faster.”

Greater injury can create greater inflammation and more pigment. Clinical improvement and treatment-induced dyschromia both appear in the evidence.[1, 2, 3, 10]

“Phototype tells you who will get PIH.”

Phototype informs caution. It does not predict the outcome of a particular person, trigger or treatment by itself.

Frequently asked questions#

Is PIH a scar?

No. PIH is a colour change after inflammation. A person can have PIH with or without textural scarring; the two need different assessment and treatment logic.

Can PIH and PIE occur together?

Yes. Inflammation can leave both pigmentary and vascular change. Treating one while ignoring the other can make results appear incomplete.[7, 8]i

Does PIH affect only darker skin?

No. It can occur in any skin. It is often more visible or persistent in darker skin, and the consequences of another inflammatory treatment may be greater.[3, 4]

Should PIH be treated while acne is active?

The acne and its inflammatory behaviour must be addressed because every new lesion can create another mark. Pigment support may form part of the plan, but it should not distract from control of the trigger.[1, 4]

Can a beauty professional use hydroquinone for PIH in the UK?

Not as a cosmetic skin-lightening product. Hydroquinone is prohibited in that cosmetic category, and medical use requires a doctor’s prescription.[11, 12]

When should a client be referred?

Refer when the diagnosis is uncertain, there is no clear preceding inflammation, the lesion is new or changing, or there is asymmetry, elevation, scale, bleeding, pain, itch or another feature inconsistent with straightforward PIH. In England the operative source is NICE NG12 — a weighted seven-point checklist scoring 3 or more, or dermoscopy suggesting melanoma — rather than any pigment-treatment review.[1, 13]

Two things that checklist will not do for you. It has no site criterion, so treat a new or changing lesion on a palm, sole or nail unit as needing assessment whatever it scores. And PIH by definition follows an identifiable inflammatory event — where there is no clear preceding inflammation, the pigment is not PIH until somebody has established what it is.[13]i

References#

Each source is graded by evidence tier. Tier 4 material (manufacturer documents, expert consensus, practitioner experience) is useful for protocol and context, and is never presented as equivalent to independent clinical evidence.

  1. Passeron T, Desai SR, Abdallah M, et al. Global consensus on the management of melanin hyperpigmentation disorders. Journal of the European Academy of Dermatology and Venereology. 2026;40(5):760–772. doi:10.1111/jdv.70185.Tier 4Supports: Classification, control of the underlying condition, photoprotection and diagnosis-specific treatment algorithms. TIER 4: this is a consensus process, not systematic evidence — the same record is carried at tier 4 in every entry that cites it. It is a pigment-management consensus and NOT a suspected-cancer referral source.Funding / interest: 'Editorial assistance was provided by Beiersdorf. The sponsor had no role in the study design, data collection, analysis, interpretation or decision to submit the manuscript.' Nine of the ten authors report conflicts of interest — consulting honoraria, lecture payments, meeting support and investigator roles across Beiersdorf, Pfizer, Incyte, AbbVie, Janssen, L'Oréal, Pierre Fabre, Novartis and others; one author declares none.
  2. Kashetsky N, Feschuk A, Pratt ME. Post-inflammatory hyperpigmentation: A systematic review of treatment outcomes. Journal of the European Academy of Dermatology and Venereology. 2024;38(3):470–479. doi:10.1111/jdv.19566.Tier 1Supports: 41 studies representing 877 patients. Complete clearance was reached in 18.1% with laser and energy-based devices, 5.4% with topicals and 2.4% with combination therapy; PIH worsened in 2.6% (8/309) of those treated with laser and energy-based devices.
  3. Mar K, Khalid B, Maazi M, et al. Treatment of Post-Inflammatory Hyperpigmentation in Skin of Colour: A Systematic Review. Journal of Cutaneous Medicine and Surgery. 2024;28(5):473–480. doi:10.1177/12034754241265716.Tier 1Supports: The limited and heterogeneous treatment evidence in skin of colour, including topical and laser outcomes.
  4. Davis EC, Callender VD. Postinflammatory Hyperpigmentation: A Review of the Epidemiology, Clinical Features, and Treatment Options in Skin of Color. Journal of Clinical and Aesthetic Dermatology. 2010;3(7):20–31.Tier 4Supports: Clinical features, epidermal-versus-dermal pigment, common triggers and cause-first management.
  5. Maghfour J, Olayinka J, Hamzavi IH, Mohammad TF. A focused review on the pathophysiology of post-inflammatory hyperpigmentation. Pigment Cell & Melanoma Research. 2022;35(3):320–327. doi:10.1111/pcmr.13038.Tier 4Supports: Proposed inflammatory and pigment mechanisms and the limits of current pathophysiological knowledge.
  6. Abad-Casintahan F, Chow SKW, Goh CL, et al. Frequency and characteristics of acne-related post-inflammatory hyperpigmentation. Journal of Dermatology. 2016;43(7):826–828. doi:10.1111/1346-8138.13263.Tier 3Supports: Frequency and reported persistence of PIH in a selected Asian acne-clinic population. Not a general-population estimate.
  7. Bae-Harboe YSC, Graber EM. Easy as PIE (Postinflammatory Erythema). Journal of Clinical and Aesthetic Dermatology. 2013;6(9):46–47.Tier 4Supports: A brief TWO-CASE commentary proposing post-inflammatory erythema terminology for persistent pink-to-red post-acne macules. It is a terminology paper, not an observational cohort and not a consensus statement: two cases cannot define frequency or every colour presentation. Typed narrative-review as the most conservative available fit, and described here so the type does not have to carry the caveat.
  8. Kalantari Y, Dadkhahfar S, Etesami I. Post-acne erythema treatment: A systematic review of the literature. Journal of Cosmetic Dermatology. 2022;21(4):1379–1392. doi:10.1111/jocd.14804.Tier 1Supports: The vascular character of post-acne erythema and the absence of a gold-standard treatment.
  9. Tan MG, Kim WB, Jo CE, et al. Topical treatment for postinflammatory hyperpigmentation: a systematic review. Journal of Dermatological Treatment. 2022;33(5):2518–2526. doi:10.1080/09546634.2021.1981814.Tier 1Supports: Comparative evidence for topical approaches, including retinoids, hydroxy acids and broad-spectrum sunscreen.
  10. Sowash M, Alster T. Review of Laser Treatments for Post-Inflammatory Hyperpigmentation in Skin of Color. American Journal of Clinical Dermatology. 2023;24(3):381–396. doi:10.1007/s40257-023-00759-7.Tier 4Supports: Variable laser outcomes, cost and risk considerations in skin of colour.
  11. British Association of Dermatologists. Melasma: Patient Information Leaflet. Updated June 2024; next review June 2027.Tier 1Supports: UK medical-prescribing boundary for hydroquinone: “Hydroquinone can only be prescribed by doctors.”
  12. Office for Product Safety and Standards. Product Safety Report: GDK Akagni Skin Toning Cream (2312-0062). Published 19 March 2024.Tier 1Supports: Enforcement finding that hydroquinone “is prohibited in this type of product” (a cosmetic skin-toning cream), citing Regulation (EC) 1223/2009 and the Cosmetic Products Enforcement Regulations 2013.
  13. National Institute for Health and Care Excellence. Suspected cancer: recognition and referral. NICE guideline NG12.Tier 1Supports: The operative suspected-cancer referral source FOR ENGLAND — pigment-treatment reviews are not. 1.7.1: refer using a suspected cancer pathway referral for melanoma if there is a suspicious pigmented skin lesion with a weighted seven-point checklist score of 3 or more. MAJOR features, 2 points each: change in size; irregular shape; irregular colour. MINOR features, 1 point each: largest diameter 7 mm or more; inflammation; oozing; change in sensation. 1.7.2: refer if dermoscopy suggests melanoma. 1.7.3: consider referral for a lesion that suggests nodular melanoma. NOTE WHAT IT DOES NOT DO: the checklist contains no site criterion, so it does not by itself prompt scrutiny of palms, soles or nail units. Wales, Scotland and Northern Ireland have their own pathways.

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Skinipedia is written by the educators at MSTA, the medic-led skincare training academy in Liverpool.