Post-inflammatory hyperpigmentation

[1] [2]

Definition and clinical frame

PIH is an acquired hypermelanosis that follows endogenous inflammation, an external injury or an iatrogenic insult. Common settings include acne, eczema, lichenoid or blistering disease, burns, scratching and procedures. The pigment should arise after the event and broadly reproduce its distribution. If there is no credible precursor, the diagnosis must be reconsidered.[3][5]

PIH can occur in any skin tone, but it is often more conspicuous and persistent in darker phototypes and may be more distressing than the original eruption. This is a population tendency, not a diagnostic criterion: skin tone does not prove PIH, and Fitzpatrick type is a sun-response scale rather than a proxy for race or ethnicity.[1][4]

The recent treatment literature is dominated by acne-associated facial PIH. In the 2024 skin-of-colour systematic review, 89% of reported cases had an inflammatory precipitant and acne accounted for most of those studied cases. Those proportions describe the included studies, not the prevalence of every cause in every population.[1]

Classification by pigment depth

The epidermal, dermal and mixed categories are clinically useful but not perfectly measured at the bedside. Colour and Wood's lamp can suggest depth; absence of enhancement does not prove dermal pigment, and Wood's lamp is less informative in very deeply pigmented skin. Histology is not routinely required solely to label depth.[5][7]

Pathophysiology

Inflammation alters communication among keratinocytes, inflammatory cells, fibroblasts and melanocytes. Cytokines, eicosanoids and growth-factor signalling can increase melanogenesis and melanosome transfer. The literature supports a multifactorial network, not one proven linear pathway, and the precise mechanisms that determine persistence remain incomplete.[3]

When the dermo-epidermal junction remains intact, excess melanin is retained in epidermal keratinocytes and can gradually leave with epidermal turnover. When interface or deeper inflammation damages the junction, melanin enters the dermis and is taken up by macrophages, producing long-lived melanophages. This explains why dermal pigment is commonly slower and less responsive to topical therapy.[3][5]

Ultraviolet radiation can darken PIH. Visible light can also induce pigmentation, especially in darker skin, although the magnitude varies by exposure and formulation. Conventional broad-spectrum sunscreen addresses ultraviolet radiation; tint produced with iron oxides or pigmentary titanium dioxide can add visible-light attenuation.[6][8]

Clinical assessment

Confirm PIH before treating pigment

1. Identify the precursor and chronology. Ask about acne, eczema, itch and scratching, infection, drug eruption, trauma, burn, hair removal or a procedure. The mark should follow the event at the same site.
2. Decide whether inflammation is still active. Erythema, scale, itch, tenderness or new primary lesions require treatment of the active dermatosis.
3. Describe morphology and distribution. PIH is usually macular. Record colour, borders and whether lesions are localised, patterned, symmetrical or generalised.
4. Estimate depth cautiously. Brown suggests an epidermal component; grey-brown or blue-grey suggests dermal pigment. Wood's lamp is optional supportive information, not a confirmatory test.
5. Ask what has already been applied. Irritating acids, retinoids, unlabelled lighteners, potent topical steroids and prolonged hydroquinone exposure can perpetuate inflammation or create another diagnosis.[4][5][7]

Dermoscopy or photography can document morphology and change, but neither replaces the history. Biopsy is reserved for an atypical, solitary, changing or otherwise concerning lesion, or when histology is needed to distinguish ochronosis, interface disease or a tumour. Routine blood tests are unnecessary for typical localised PIH; investigations follow the suspected alternative diagnosis.[5][7]

What if a brown mark does not enhance with Wood's lamp?

Do not relabel it automatically as dermal PIH. Recheck the precursor and distribution, examine in good light, consider mixed pigment and remember that Wood's lamp has limited utility in deeply pigmented skin. Use the whole clinical picture; biopsy only when the lesion is atypical or the diagnosis remains consequentially uncertain.

[5] [7]

Differential diagnosis

Management principles

1. Stop new pigment formation

Treat the active cause and reduce avoidable irritation. In acne-associated PIH, a tolerable acne regimen is more important than repeatedly adding lighteners; excessive dryness or dermatitis can create further pigment. Address picking, scratching and friction without blaming the patient.[4][6]

2. Photoprotect

Use a broad-spectrum sunscreen that the patient will apply consistently, together with shade and clothing. A tinted product containing iron oxides is a reasonable option where visible-light-induced pigmentation is a concern, but shade match, tolerability, access and adherence matter. Avoid the absolute claim that one sunscreen makes every other treatment succeed or fail.[6][8]

3. Select topical therapy with a low-irritation plan

Common clinician-selected options include hydroquinone, topical retinoids and azelaic acid. Hydroquinone inhibits melanin synthesis; retinoids increase epidermal turnover and can simultaneously treat acne; azelaic acid combines pigment-directed and anti-acne effects. Niacinamide and other cosmeceutical agents are alternatives, but product quality and PIH-specific evidence vary.[1][2][6]

Start one compatible regimen gently, use a bland moisturiser when needed and review tolerability before escalation. Hydroquinone availability and permitted concentration differ by jurisdiction; use should be time-limited and clinician-supervised. Prolonged or high-concentration misuse is associated with exogenous ochronosis. Retinoids and any agent that causes dermatitis can worsen pigmentation through renewed inflammation.[6][7]

Fixed triple-combination products and many lightening ingredients are better studied in melasma than PIH. They should not be presented as universally superior PIH therapy. Oral tranexamic acid has reported efficacy in melasma, but this does not establish routine systemic treatment for PIH; its potential thromboembolic risk makes casual extrapolation unsafe.[1][2][11]

4. Reserve procedures for selected patients

Chemical peels, laser and energy-based devices may produce partial improvement, but results depend on cause, depth, device, operator and skin response. Procedures can also induce or worsen PIH. Use an experienced clinician, conservative parameters, test areas where appropriate and clear counselling rather than a fixed device hierarchy.[1][2][6]

In the 2024 systematic review of 41 studies and 877 patients, complete response was reported in 18.1% after laser or energy-based treatment, 5.4% after topical treatment and 2.4% after combination therapy; laser or energy-based treatment worsened PIH in 2.6%. Most included cases were acne-associated, outcomes were heterogeneous and these pooled proportions should not be promised to an individual patient.[2]

Follow-up and prognosis

Photographs under consistent lighting are more useful than promises tied to a fixed month. Review the active dermatosis, adherence, irritation, new exposures and change in pigment. Epidermal PIH often improves over months; dermal pigment can persist for years. Treatment studies report much more partial than complete response, so shared goals may be lightening, prevention of new marks and reduced distress rather than complete eradication.[1][2]

No improvement should trigger a check of diagnosis, continuing inflammation, adherence and exposure rather than automatic laser escalation. A changing morphology, no credible precursor or systemic distribution requires a different diagnostic pathway.[5][7][10]

Special populations

• Pregnancy or lactation: prioritise treatment of the underlying dermatosis and photoprotection. Hydroquinone and topical retinoids are generally avoided because of limited pregnancy safety data; discuss a locally accepted alternative such as azelaic acid with the treating clinician.
• Children: treat the cause, minimise friction and use age-appropriate photoprotection. Potent or compounded lighteners should not be started without specialist advice.
• Darker phototypes: acknowledge higher visibility, persistence and procedural dyspigmentation risk without treating skin tone as a diagnosis. Use tolerable regimens and conservative procedures.
• Prior unlabelled lighteners: inspect products when possible. Consider irritant dermatitis, topical-steroid damage, mercury exposure and ochronosis rather than simply adding another depigmenting agent.[1][6][7]

Evidence limits

The two 2024 systematic reviews found heterogeneous study designs, causes, outcome measures and follow-up. Complete clearance was uncommon, much of the evidence concerned acne-associated facial PIH, and adverse darkening occurred after some procedures. Therefore, a source-first answer should describe options and trade-offs rather than a universal ladder, fixed clearance time or guaranteed response.[1][2]

[1] [2] [5] [8] [11]

Red Flags

[5] [7] [10]

Exam application bank

Worked stem 1 — classic acne-associated PIH

A patient with darker phototype has brown macules exactly where acne papules healed. Diagnose PIH clinically, document whether acne remains active, use colour and optional Wood's lamp only as supportive depth clues, review products and light exposure, then treat acne, minimise irritation, photoprotect and discuss a topical option with realistic expectations.[4][5][6]

Worked stem 2 — apparent treatment failure

At review, first confirm use and tolerability, look for ongoing acne or dermatitis, check whether the lightener itself is irritating the skin and reconsider the diagnosis. Do not convert “no early response” into a guaranteed indication for a peel or laser.[1][2]

Worked stem 3 — differential trap

Symmetric facial patches without prior inflammation suggest melasma; blue-black facial change after prolonged lightener use suggests ochronosis; generalised pigment with oral-mucosal or palmar-crease involvement and systemic symptoms suggests a systemic disorder such as adrenal insufficiency; a solitary changing lesion requires tumour assessment.[7][10]

[1] [2]

References

1. [1]Mar K, Khalid B, Maazi M, et al. Treatment of Post-Inflammatory Hyperpigmentation in Skin of Colour: A Systematic Review. J Cutan Med Surg, 2024.PMID 39075672
2. [2]Kashetsky N, Feschuk A, Pratt ME. Post-inflammatory hyperpigmentation: A systematic review of treatment outcomes. J Eur Acad Dermatol Venereol, 2024.PMID 37843491
3. [3]Maghfour J, Olayinka J, Hamzavi IH, et al. A Focused review on the pathophysiology of post-inflammatory hyperpigmentation. Pigment Cell Melanoma Res, 2022.PMID 35306737
4. [4]Elbuluk N, Grimes P, Chien A, et al. The Pathogenesis and Management of Acne-Induced Post-inflammatory Hyperpigmentation. Am J Clin Dermatol, 2021.PMID 34468934
5. [5]Silpa-Archa N, Kohli I, Chaowattanapanit S, et al. Postinflammatory hyperpigmentation: A comprehensive overview: Epidemiology, pathogenesis, clinical presentation, and noninvasive assessment technique. J Am Acad Dermatol, 2017.PMID 28917451
6. [6]Chaowattanapanit S, Silpa-Archa N, Kohli I, et al. Postinflammatory hyperpigmentation: A comprehensive overview: Treatment options and prevention. J Am Acad Dermatol, 2017.PMID 28917452
7. [7]Wang RF, Ko D, Friedman BJ, et al. Disorders of hyperpigmentation. Part I. Pathogenesis and clinical features of common pigmentary disorders. J Am Acad Dermatol, 2023.PMID 35151757
8. [8]Lyons AB, Trullas C, Kohli I, et al. Photoprotection beyond ultraviolet radiation: A review of tinted sunscreens. J Am Acad Dermatol, 2021.PMID 32335182
9. [9]Narayan R V, Thakur V, Bishnoi A, et al. Acquired dermal macular hyperpigmentation: a unified spectrum of dermal pigmentary dermatoses. Clin Exp Dermatol, 2026.PMID 41700520
10. [10]Bornstein SR, Allolio B, Arlt W, et al. Diagnosis and Treatment of Primary Adrenal Insufficiency: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab, 2016.PMID 26760044
11. [11]Sheu SL. Treatment of melasma using tranexamic acid: what's known and what's next. Cutis, 2018.PMID 29554171