PIH vs Melasma: Differentiating & Treating
How to reliably separate post-inflammatory hyperpigmentation from melasma using history, distribution, Wood's lamp and trigger pattern — and why the distinction redirects treatment, because PIH can resolve while melasma must be managed for life.
Distinguishing post-inflammatory hyperpigmentation (PIH) from melasma is one of the highest-yield decisions in pigmentary dermatology, because the two look similar in Fitzpatrick IV–VI skin yet carry different causes, different prognoses and partly different treatments. PIH is pigment laid down in response to a prior inflammatory insult and tends to resolve once that trigger is removed and the skin is protected. Melasma is a chronic, symmetric, photo-hormonal disorder that must be managed indefinitely. Getting this right changes both the plan you write and the prognosis you give — and the two frequently coexist, so the real skill is recognising both at once.
The four discriminators
Most cases separate cleanly on history, distribution, Wood's lamp and trigger pattern.
History does most of the work. A patient who points to spots exactly where pimples healed has PIH; a patient with a symmetric brown patch across both cheeks that worsens every summer and appeared in pregnancy has melasma. Distribution confirms it: PIH follows the footprint of the original inflammation and is often asymmetric, while melasma is strikingly symmetric and patterned. Wood's lamp then grades depth — epidermal pigment brightens under the lamp, dermal pigment does not — which matters for both conditions but is classically used to characterise melasma. Finally, the course is diagnostic in retrospect: PIH improves once you control its driver; melasma keeps flaring with sun, light and hormones.
Side-by-side
| Feature | Post-inflammatory hyperpigmentation (PIH) | Melasma |
|---|---|---|
| Cause | A prior inflammatory insult (acne, injury, procedure, dermatosis) | Chronic photo-hormonal; UV, visible light, hormones |
| Distribution | Maps to prior inflammation; often asymmetric/scattered | Symmetric, patterned (malar/centrofacial/mandibular) |
| Onset clue | Spots where lesions/injury healed | Patches appearing/worsening with sun, pregnancy, OCPs |
| Wood's lamp | Used to grade epidermal vs dermal depth | Accentuation indicates epidermal; no change indicates dermal |
| Natural course | Tends to resolve once trigger removed + protected | Chronic, relapsing — does not self-resolve |
| Prognosis to give | "This should fade with control and time" | "We manage this long-term to keep it suppressed" |
Why the distinction redirects treatment
The shared ground is large — both are treated with gentle, low-inflammation superficial approaches, tyrosinase inhibition, turnover acceleration and strict photoprotection, and both are made worse by aggressive procedures in skin of color. But the emphasis and the prognosis diverge:
- For PIH, the first move is to switch off the source of inflammation. Treating the active acne, eczema or trigger is the actual treatment; the pigment then fades with topical tyrosinase inhibition, gentle resurfacing and protection. Because PIH is self-limiting once the driver stops, you can promise genuine fading over months — and you must avoid causing new PIH with over-aggressive treatment.
- For melasma, there is no upstream lesion to switch off — the "trigger" is UV, visible light and hormones, which persist. So treatment is a continuous multi-pathway management programme (see the protocols lesson) with lifelong photoprotection, and the prognosis is honest stabilisation, not cure.
When they coexist — very common in acne-prone Fitzpatrick IV–VI skin — treat the inflammatory driver of the PIH and run the melasma management in parallel, keeping the whole regimen low-inflammation so you do not generate fresh PIH on top of the melasma.
A practical note on a third mimic: drug-induced or lichenoid pigmentation and exogenous ochronosis (from prolonged high-strength hydroquinone misuse) can imitate refractory melasma. If pigment is worsening despite appropriate treatment, reconsider the diagnosis before escalating.
Key takeaway
Separate PIH from melasma on history, distribution, Wood's lamp and course: PIH follows a prior inflammatory insult, maps to where it was, and fades once the trigger stops; melasma is symmetric, patterned, photo-hormonal and chronic. The distinction redirects treatment — switch off the inflammation driving PIH and reassure that it will fade, but manage melasma continuously with multi-pathway therapy and lifelong photoprotection. When both are present, treat the PIH trigger and stabilise the melasma together, keeping everything low-inflammation so you do not create the very pigment you are trying to clear.
Frequently asked questions
How do I tell PIH and melasma apart in clinic?
Start with history and distribution: PIH follows a prior inflammatory event (acne, injury, a procedure) and maps to where that was, often asymmetrically; melasma is symmetric and patterned across the cheeks, central face or jawline and worsens with sun and hormones. Use Wood's lamp to grade depth, and consider the course — PIH fades once its trigger is controlled, while melasma keeps relapsing. The two also frequently coexist.
Does Wood's lamp diagnose melasma?
Wood's lamp does not diagnose melasma by itself, but it characterises pigment depth in both conditions: epidermal pigment accentuates under the lamp while dermal pigment does not. That information helps set expectations — epidermal pigment responds better to topicals and gentle peels, dermal pigment is more resistant — and supports the clinical picture built from history and distribution.
Why does it matter whether pigment is PIH or melasma?
Because the prognosis and emphasis differ. PIH is driven by a prior inflammatory insult and tends to resolve once that driver is switched off and the skin is protected, so you can promise gradual fading. Melasma is chronic and photo-hormonal with no single upstream lesion to remove, so it needs continuous multi-pathway management and lifelong photoprotection. Treating one as the other wastes months and can provoke flares.
Can a patient have both PIH and melasma at the same time?
Yes, very commonly — especially in acne-prone Fitzpatrick IV–VI skin. The approach is to treat the inflammatory driver of the PIH (for example, control the acne) while running melasma management in parallel, keeping the whole regimen gentle and low-inflammation so that treatment itself does not generate new post-inflammatory pigment on top of the melasma.