What Is PIH and How Is It Different from Melasma?
Share
If you've ever had acne and been left with dark marks, or developed brown patches on your face that appeared gradually over months — you've encountered either PIH or melasma, or possibly both at the same time.
These two conditions are frequently confused with each other. They both produce darker patches on the skin. They both respond to similar brightening actives. And on Indian skin, they both tend to be more intense and more persistent than on lighter skin types.
But they have completely different causes, different patterns, different timelines, and different underlying drivers — which means effective treatment for one doesn't automatically mean effective treatment for the other.
Quick Answer
Post-inflammatory hyperpigmentation (PIH) is a flat, dark mark left on the skin after an inflammatory event — acne, rash, insect bite, scratch, or any skin trauma. It results from cytokines released during inflammation stimulating melanocytes to produce excess melanin at the site. Melasma is a chronic condition driven by hormones, UV exposure, and heat — not by a specific inflammatory event. It presents as symmetrical patches across both cheeks, forehead, and upper lip. PIH appears asymmetrically at the site of injury and may be one-sided; melasma is almost always bilateral and symmetrical. Both are treated with similar brightening actives, but melasma requires longer treatment and ongoing trigger management that PIH does not.
What Is PIH — The Complete Definition
Post-inflammatory hyperpigmentation (PIH) is a form of acquired hyperpigmentation that occurs as a consequence of skin inflammation. As documented in a PubMed-indexed systematic review on PIH treatment in skin of colour (PMC11514325), PIH is characterised by an excess production or deposition of melanin in the epidermis and/or dermis, resulting from inflammation. The darkening is attributed to activation of melanocytes by inflammatory mediators — specifically cytokines released during the inflammatory response that signal melanocytes to produce more melanin as part of the healing process.
The same review specifically notes that PIH tends to be more prominent and enduring in individuals with darker skin tones, particularly Fitzpatrick types III–VI — who have an increased size of melanosomes, quantity of melanin, and increased eumelanin.
In practical terms: any time the skin experiences inflammation — from acne, eczema, psoriasis, rash, insect bite, scratch, friction, or even aggressive skincare — the inflammatory cytokines activate nearby melanocytes. Those melanocytes produce excess melanin at the inflammation site. When the inflammation resolves, the excess melanin remains — visible as a flat, dark mark at exactly the location where the original inflammatory event occurred.
What Is Melasma — The Complete Definition
Melasma is a specific, chronic form of facial hyperpigmentation driven primarily by three simultaneous triggers: UV radiation, hormonal changes (estrogen, progesterone), and heat. It is not caused by a specific inflammatory event — it develops gradually over weeks as an ongoing hormonal-UV-heat interaction continuously overstimulates melanocytes in certain facial zones.
The characteristic presentation is symmetrical. Melasma almost always appears on both sides of the face simultaneously — bilateral patches on the cheeks, forehead, upper lip, and occasionally the jawline. A strictly one-sided patch is clinically unlikely to be melasma; asymmetric pigmentation is far more characteristic of PIH or localised sun damage.
Melasma is more common in women — accounting for approximately 90% of cases — and is particularly prevalent during periods of hormonal change: pregnancy (where it's called chloasma or the "mask of pregnancy"), use of oral contraceptives, thyroid disorders, and PCOS. It affects darker skin phototypes more frequently and more intensely — including Indian Fitzpatrick III–V skin — because eumelanin-dominant skin responds more intensely to the UV and hormonal triggers driving it.
The Critical Differences — Side by Side
| Parameter | PIH | Melasma |
|---|---|---|
| Cause | Specific inflammatory event (acne, injury, rash) | Hormones + UV + heat — chronic, ongoing triggers |
| Pattern | Asymmetric; appears at exact site of inflammation | Symmetric; bilateral — both cheeks, forehead, upper lip |
| Onset | Appears directly after or during healing of inflammation | Develops gradually over weeks to months |
| Borders | Irregular, following the shape of the original lesion | More defined, can be reticulated (lacy) pattern |
| Self-resolution | Fades in 6–12 months without treatment on lighter skin; longer on Indian skin | Does not self-resolve; persists and worsens with ongoing triggers |
| Affected population | Any skin type, any age | Predominantly women; more common and severe in Fitzpatrick III–VI |
| Primary driver | Cytokine-mediated melanocyte activation during inflammation | Hormonal stimulation + UV + heat |
| Treatment duration | 8–12 weeks typically sufficient for post-acne PIH | 3–6 months for initial clearing; requires ongoing maintenance |
| Recurrence risk | Low — if the original trigger (acne, friction) is managed | High — melasma recurs with UV, heat, or hormonal changes even after clearing |
How to Tell Them Apart — The Clinical Tests
The Symmetry Test
This is the fastest clinical distinction. Look at both sides of your face simultaneously.
If the pigmentation is on both cheeks in approximately the same areas — symmetrical, bilateral — melasma is far more likely. The centrofacial pattern (both cheeks, nose, and forehead in a butterfly shape) accounts for 50–80% of melasma cases.
If the pigmentation is on one side only, or asymmetric — more on the right than left, or in an irregular pattern that doesn't mirror — PIH or localised photodamage is more likely. A strictly one-sided patch is clinically unlikely to be melasma.
The Origin Test
Can you trace the dark spot back to a specific event? A pimple that healed. A rash. A scratch. An insect bite. A burn. If the answer is yes, and the dark mark appeared in that exact location shortly after the event — it's PIH.
Did the patches appear gradually, without a specific triggering skin event, often during pregnancy, contraceptive use, or after moving to a sunnier climate? That pattern is consistent with melasma.
The Wood's Lamp Test (Clinical)
A Wood's lamp (UV lamp) helps dermatologists determine whether hyperpigmentation is epidermal or dermal. Under UV light, epidermal pigmentation enhances (appears darker) while dermal pigmentation doesn't enhance clearly. This distinction matters for both PIH and melasma because deeper, dermal pigmentation is harder to treat topically and may require additional clinical procedures.
Why Both Are More Severe on Indian Skin
The systematic review on PIH in skin of colour (PMC11514325) specifically documents that individuals with Fitzpatrick types III–VI have larger melanosomes, more melanin quantity per cell, and more eumelanin — all of which make both PIH and melasma more visually intense and longer-lasting on Indian skin than on lighter skin types.
For PIH specifically: the same acne pimple that leaves no visible mark on Fitzpatrick II skin can leave a dark mark lasting 6–12 months on Fitzpatrick V skin. This isn't because Indian skin heals poorly — it's because Indian skin's melanocytes respond more intensely to the inflammatory signal, producing more melanin per inflammatory event.
For melasma specifically: Indian skin's higher eumelanin density means that when hormonal and UV triggers overstimulate melanocytes, the resulting pigmentation is denser, appears darker, and takes longer to clear than the same triggers would produce on lighter skin.
PIH and PIE — Another Distinction Worth Knowing
PIH is sometimes confused with a related but different condition: Post-Inflammatory Erythema (PIE).
PIH — excess melanin deposition — appears as flat brown, dark brown, or grey-black marks. More common in Fitzpatrick III–VI skin (Indian skin).
PIE — dilated blood vessels (erythema) — appears as flat red or pink marks. More common in Fitzpatrick I–II skin (lighter skin types).
On Indian skin, PIH is more common than PIE because the melanin response to inflammation is more intense than the vascular response. However, some Indian skin types — particularly those in the lighter Fitzpatrick III range — can have both simultaneously, with a reddish-pink mark that also has a brown undertone.
The distinction matters because PIE responds to anti-vascular ingredients (niacinamide's redness-reduction action is particularly relevant here) and certain laser treatments, while PIH responds to tyrosinase inhibitors and melanin transfer blockers.
What PIH and Melasma Both Respond To — The Shared Treatment Layer
Despite their different causes, the downstream mechanism that makes both conditions visible is the same: excess melanin produced by melanocytes and transferred to surface skin cells. This means the same brightening actives address both conditions, though for different durations and with different additional steps.
Alpha Arbutin (1%) — inhibits tyrosinase, slowing melanin production. Directly applicable to PIH (where inflammation upregulated tyrosinase) and melasma (where hormones and UV upregulated it). The 2025 Indian women clinical trial (PMC11822242) showed 16.3% melanin reduction and 18.4% melasma improvement in 90 days with zero irritation.
TYROSTAT-09 (1%) — second tyrosinase inhibitor through a different molecular mechanism. Particularly strong evidence for melasma — a published RCT found it comparable to hydroquinone 4% for melasma.
Niacinamide (3%) — blocks melanosome transfer downstream. Addresses the step that makes excess melanin visible at the surface. Equally relevant for PIH (blocking transfer of inflammation-triggered melanin) and melasma (blocking transfer of hormonally-triggered melanin).
Ethyl Ascorbic Acid (0.5%) — neutralises UV-triggered oxidative stress that re-activates melanocytes daily. More critical for melasma (where UV is a primary ongoing trigger) but also prevents UV from extending PIH duration.
Daily SPF 50+ — the most important concurrent step for both conditions. UV keeps both PIH darker and melasma continuously active.
Ocevia Skin Brightening Cream combines all four actives — covering the shared treatment layer for both PIH and melasma. Used twice daily with daily SPF, it is appropriate for both conditions — with the understanding that PIH typically responds in 8–12 weeks while melasma requires 3–6 months and ongoing maintenance.
What PIH Needs That Melasma Doesn't
Treat the active trigger. For PIH, the original inflammatory trigger (usually acne) must be treated to prevent new PIH from forming while existing marks are being faded. Brightening cream fades existing PIH — acne management prevents new PIH. Without both, the routine is always playing catch-up.
Don't pick. Picking inflamed skin increases the depth and intensity of the inflammatory event, producing darker, longer-lasting PIH. On Indian skin, the difference between a pimple that heals as a light mark vs one that heals as a deep dark mark is often picking vs not picking.
What Melasma Needs That PIH Doesn't
Hormonal trigger management. Melasma's primary driver is hormonal — estrogen and progesterone stimulating melanocytes. Topical treatment manages the visible result, but if the hormonal trigger is untreated (unmanaged thyroid, PCOS, contraceptive use, stress), melasma will continue reforming. A dermatologist or endocrinologist consultation alongside topical treatment produces significantly better long-term outcomes for hormonal melasma.
Heat management. Heat independently activates melanocytes in melasma-prone skin — independent of UV. Avoiding facial steaming, hot showers on the face, and direct heat exposure reduces a trigger that PIH skin doesn't respond to in the same way.
Tinted SPF with iron oxide. For melasma patients, visible light is an additional trigger that standard SPF doesn't block. Iron oxide in tinted SPF specifically blocks visible light — a meaningful additional protection for melasma that standard clear SPF doesn't provide.
Myth vs Fact
Myth: PIH and melasma are the same condition — just different words for dark spots. Fact: They share a common endpoint (excess melanin) but have completely different causes, patterns, timelines, and management needs. PIH is caused by a specific inflammatory event; melasma is driven by chronic hormonal, UV, and heat triggers. PIH is asymmetric; melasma is bilateral and symmetrical. PIH is effectively managed in 8–12 weeks; melasma requires months of treatment and ongoing maintenance. Treating both identically produces suboptimal results for melasma specifically.
Myth: If a brightening cream worked for PIH, it will work equally well and equally fast for melasma. Fact: The same actives work for both, but melasma responds more slowly because its triggers are ongoing rather than resolved. PIH has a resolved past trigger — the inflammation ended and the treatment has a clear target. Melasma's triggers (hormones, UV, heat) remain active throughout treatment. This is why PIH typically shows significant improvement in 8–12 weeks while melasma requires 3–6 months and maintenance.
Myth: Once melasma is cleared, it won't come back. Fact: Melasma is a chronic condition driven by melanocyte sensitivity to hormonal and UV triggers. Those triggers don't disappear when the visible patches lighten. Without ongoing maintenance — daily SPF, continued brightening treatment at maintenance frequency, and trigger management — melasma recurs in most patients within months of stopping treatment. This is a management condition, not a one-time cure.
Quick Tips
- Use symmetry as your first diagnostic tool — bilateral, both-cheeks-simultaneously patches strongly suggest melasma; asymmetric, one-sided, or spot-specific marks strongly suggest PIH
- If you have active acne alongside PIH, treat both simultaneously — a brightening cream fades existing marks but won't stop new ones from forming if active acne continues; both problems need concurrent treatment
- For melasma, upgrade to tinted SPF with iron oxide — visible light is a specific melasma trigger that standard SPF doesn't block; this single change makes a meaningful difference in melasma management without changing any other part of the routine
- Give PIH 8–12 weeks and melasma 3–6 months — switching products before these timelines provides no useful information about efficacy; the biology of clearing melanin takes this long regardless of which valid brightening active is used
- If melasma is hormonally driven, address the underlying cause alongside topical treatment — PCOS, thyroid disorders, and specific contraceptive choices all affect how well melasma responds to topical brightening; topical treatment alone is less effective when the hormonal signal continues unchecked.
