Post-inflammatory hyperpigmentation (PIH) and post-inflammatory erythema (PIE) are distinct sequelae of skin inflammation. PIH results from excess melanin deposition and presents as brown, tan, or grey marks that do not change under pressure. PIE is vascular in origin, presenting as pink or red patches that blanch when pressed. The treatments diverge significantly, so correct identification before any pigment protocol is essential.
What Is Post-Inflammatory Hyperpigmentation?
Post-inflammatory hyperpigmentation develops when skin inflammation stimulates excess melanin production, leaving persistent discolouration after the primary lesion resolves. The JAAD's comprehensive review describes it as one of the most common pigmentary disorders seen in clinical practice, with disproportionate representation in Fitzpatrick types III–VI.
The clinical picture ranges from light tan to dark brown or slate grey, depending on where the melanin has accumulated. Epidermal PIH, confined to the upper skin layers, responds well to depigmenting protocols. Dermal PIH, where melanin has migrated into the dermis and been phagocytosed by macrophages, is considerably more resistant to topical treatment. The distinction matters because it shapes the intervention plan before the first product is chosen.
Common triggers include acne, eczema, psoriasis, contact dermatitis, and procedural injury from lasers, chemical peels, or microneedling. In susceptible patients, even a mild cutaneous insult can leave marks that outlast the original problem by months or, in dermal presentations, years.
What Is Post-Inflammatory Erythema?
Post-inflammatory erythema is not a pigmentation disorder. It is a vascular sequela. Residual dilation or damage to superficial dermal capillaries after inflammation leaves pink, red, or mauve marks once the active lesion has cleared. PIE is most commonly seen after acne, and its red-mark phase is often the presenting complaint, sometimes mislabelled by patients as scarring or hyperpigmentation.
PIE occurs across all Fitzpatrick types but is easiest to appreciate visually in types I–III, where the contrast against a lighter baseline is most obvious. In darker skin types, active erythema can be harder to identify and more easily confused with early PIH. That is precisely why a structured assessment step matters before treatment planning begins.
How to Differentiate PIH from PIE in Consultation
The blanch test is the most practical bedside tool. Press a glass slide or a clean fingertip firmly against the mark for two to three seconds. A mark that turns white or significantly fades under pressure is vascular. That is PIE. A mark that holds its colour is melanin-based. That is PIH. The test is reliable across skin types and requires no specialist equipment.
Dermoscopy adds a useful second layer. A 2025 study in JEADV Clinical Practice found dermoscopic evaluation reliably differentiated erythema from PIH in skin of colour patients, with the two conditions showing distinct vascular versus pigmented patterns. Under dermoscopy, PIE characteristically shows dotted or linear vessels without a pigmented background. PIH presents as diffuse brown-to-grey pigmentation without significant vascular architecture.
Wood's lamp examination helps stratify PIH by depth. Epidermal PIH becomes more pronounced under Wood's lamp; dermal PIH does not enhance. This directly shapes the treatment plan, since dermal presentations need a different and often more cautious approach. Wood's lamp adds little for PIE, because vascular marks do not respond to melanin-targeted illumination.
A workable clinical sequence:
- Blanch test. Blanches: PIE. Does not blanch: PIH.
- For PIH: Wood's lamp to assess epidermal versus dermal depth.
- Standardised photography at each visit to track response over time.
Where both conditions coexist, as happens after severe inflammatory acne where deep lesions cause simultaneous vascular injury and melanocyte stimulation, sequential management tends to produce better outcomes than attempting to treat both at once. Addressing the vascular component first, then the pigment, gives each intervention a cleaner baseline to work from.
Why the Distinction Determines the Treatment Plan
Applying the wrong pathway adds consultation cycles, frustrates the patient, and misses windows for early resolution.
PIE responds to approaches targeting the vasculature: pulsed dye laser, Nd:YAG, and intense pulsed light with appropriate cut-off filters. Topical options include niacinamide and azelaic acid, the latter carrying both anti-inflammatory and mild vascular effects. Early PIE, addressed within the first six to twelve weeks, often responds better than established vascular marks where the capillaries have become more fixed.
PIH requires melanin-targeted intervention. The evidence base covers retinoids (which accelerate epidermal turnover and suppress post-inflammatory melanocyte activity), tyrosinase inhibitors including azelaic acid, kojic acid, and niacinamide, and carefully timed chemical exfoliation. Evidence on tranexamic acid for PIH has grown substantially in recent years. The full evidence review covers what the clinical literature currently supports.
In both PIH and PIE, photoprotection is non-negotiable. Ultraviolet exposure drives ongoing melanogenesis in PIH and sustains the vasodilation that maintains PIE. Broad-spectrum SPF 30 or higher, reapplied throughout the day, is not optional for either pathway.
PIH Assessment in Skin of Colour
Practitioners working with Fitzpatrick types IV–VI encounter a higher background rate of PIH, more severe clinical presentations, and a narrower margin for procedural error. Before any energy-based or ablative procedure in these skin types, risk stratification should include current pigmentation status, personal history of PIH, and an honest assessment of whether the planned intervention threshold is appropriate.
Wood's lamp is less reliable for depth stratification in darker skin types because high baseline melanin content reduces the contrast needed to localise epidermal pigment. In those cases, clinical response to a four-to-six-week topical retinoid trial can give more useful depth information than the lamp alone.
Dermoscopy, as noted in the JEADV paper, remains valuable across skin types. The blanch test is equally valid regardless of baseline skin tone, since it relies on vascular physiology rather than visual contrast. These are the tools that make consistent clinical decisions possible across a diverse patient population.
The free pigmentation quiz is a useful structured starting point before a detailed clinical pigment assessment. It maps the pattern and helps identify where the evaluation should focus.
Hyperpigmentation presentations, PIH included, are among the most frequent concerns the clinic sees week in, week out. Hyperpigmentation Decoded is the four-module programme built from the same assessment and sequencing framework used in clinical practice, covering the full picture from initial assessment through to protocol design across Fitzpatrick types. At £150 with lifetime access, it is the reference to return to when a new pigment presentation arrives in clinic.
FAQ
How do I quickly tell PIH and PIE apart at the point of care? Use the blanch test. Press a clean glass or fingertip firmly against the mark for two to three seconds. A mark that fades or turns white under pressure is vascular (PIE). A mark that holds its colour is melanin-based (PIH). The test works reliably across all Fitzpatrick types and needs no equipment.
Can a patient have PIH and PIE at the same time? Yes, particularly after severe inflammatory acne where deep lesions cause both vascular injury and melanocyte stimulation. Standardised photography and a clear record of which marks blanch and which do not keeps the two pathways separate. Sequential treatment, vascular first then pigment, tends to give cleaner results than treating both simultaneously.
Does PIH always respond to topical depigmenting agents? Epidermal PIH generally does, given time and consistent photoprotection. Dermal PIH is much more resistant because melanin has migrated below the reach of most topical agents. Wood's lamp assessment, where reliable, helps distinguish the two. Poor response to a three-to-four-month topical programme should prompt consideration of dermal deposition and an adjusted strategy.
How long does PIE typically take to resolve without treatment? PIE can persist for three to twenty-four months without intervention. Vascular laser treatment, pulsed dye laser in particular, significantly accelerates resolution in most patients, with meaningful improvement often seen after one to three sessions. The earlier treatment begins, before the capillaries become more fixed, the better the response tends to be.
Is sunscreen relevant for PIE or just PIH? For both. Ultraviolet exposure drives melanogenesis in PIH directly. In PIE, sun exposure causes cutaneous vasodilation and sustains the inflammation that keeps vascular marks active. Broad-spectrum SPF 30 or higher is relevant regardless of whether the presentation is PIH, PIE, or mixed.
What role does Fitzpatrick type play in PIH assessment? Fitzpatrick type shapes both the likelihood of PIH and the tools available to assess it. Higher Fitzpatrick types face greater risk of PIH after any cutaneous insult, and visual assessment of erythema can be harder in darker skin. The blanch test remains valid across all types; Wood's lamp has more limited utility in types V–VI. A structured clinical approach, as outlined by Bernadette Tobin RN, MSc, helps practitioners make consistent decisions regardless of baseline skin tone.