Post-Inflammatory Pigmentation vs Melasma: How to Tell the Difference and Treat Each Correctly

Post-inflammatory pigmentation (PIH) is the skin's response to injury. A pimple, a rash, a burn, a bout of eczema, any of these can trigger localised melanin overproduction as the skin tries to repair itself. The result is a flat, darkened mark that sits exactly where the original wound was. Melasma is different. It is a chronic pigmentation disorder driven by a combination of hormonal activity, UV exposure, and genetic susceptibility. It appears in symmetrical patches, both cheeks, the forehead, the upper lip, and it tends to be diffuse rather than spot-specific.
On deeper Indian skin tones, both conditions show up as brown to greyish-brown discolouration, which is why they get conflated so often. The confusion is not cosmetic vanity. It has treatment consequences.
Location is the first clue. PIH follows the injury, a cluster of old acne marks on the jaw, a dark streak where a burn healed, a patch where contact dermatitis settled. It does not respect symmetry. Melasma, by contrast, is almost always bilateral. If you see matching patches on both cheekbones, or a band across the forehead, melasma is more likely.
Onset history matters too. PIH has a clear predecessor, the patient can usually point to the wound that caused it. Melasma often begins or worsens during pregnancy (the reason it was once called the mask of pregnancy), after starting oral contraceptives, or after prolonged sun exposure without adequate protection. A dermatologist will ask about both hormonal history and skin injury history before making a call.

Under a Wood's lamp, an ultraviolet light device used in clinical settings, epidermal PIH appears more defined and darker, while melasma can show both epidermal and dermal involvement. Dermal melasma, where the excess melanin has settled into deeper skin layers, is significantly harder to treat and does not respond well to surface-level products. This distinction alone changes the entire approach to treatment.
PIH is caused by inflammation triggering melanocytes, the cells that produce melanin, to overproduce as part of the healing cascade. Once the inflammation is resolved, the melanin overproduction stops. What remains is essentially a stain. The treatment goal is to fade existing hyperpigmentation and prevent new inflammation from creating new marks.

Melasma is a regulation problem. The melanocytes are not responding to injury; they are responding to oestrogen, progesterone, and UV radiation in a way that healthy melanocytes do not. This is why melasma can return within days of sun exposure even after successful treatment. Clearing the visible pigmentation does not fix the underlying sensitivity. A 2022 review published in the Journal of the American Academy of Dermatology confirmed that melasma recurrence rates remain high even with combination therapy, because the trigger, hormonal sensitivity amplified by UV, is not eliminated by topical agents alone.
This is the core reason treating PIH with melasma protocols, or vice versa, produces poor results. Aggressive chemical peels used for melasma can worsen PIH by creating new inflammation. Gentle brightening serums adequate for mild PIH will barely touch dermal melasma.

For PIH, the treatment sequence is: resolve the source of inflammation first, then address the pigmentation. If the PIH comes from acne, uncontrolled acne means new PIH will keep forming regardless of how many brightening products are applied. Niacinamide (at 5 to 10%) inhibits the transfer of melanin to skin cells and has a strong safety record across skin tones. Azelaic acid addresses both residual inflammation and pigmentation simultaneously, making it particularly useful for post-acne PIH. Vitamin C serums help with surface-level brightening. For stubborn marks, a dermatologist may recommend a low-strength retinoid to accelerate cell turnover.
For melasma, the standard first-line treatment remains a combination of hydroquinone, a retinoid, and a mild topical corticosteroid, a formulation often called the Kligman formula. Tranexamic acid, available both topically and as an oral supplement under medical supervision, has shown strong results specifically for melasma in studies on Asian and South Asian skin. A 2020 study in the Indian Journal of Dermatology, Venereology and Leprology found oral tranexamic acid at 250mg twice daily produced significant lightening in patients with recalcitrant melasma. Chemical peels, glycolic acid or salicylic acid at appropriate concentrations, can be used for melasma but require careful management to avoid triggering rebound inflammation, especially in Indian skin tones that are more prone to post-procedure PIH.
For PIH, sunscreen prevents UV from darkening existing marks further. Melanin in a healing patch oxidises and deepens with sun exposure, which is why a mark that might have faded in a few months can persist for years without consistent sun protection. A broad-spectrum SPF 50 applied every morning, and reapplied if outdoors, is standard advice from any dermatologist managing PIH in Indian patients.
For melasma, sunscreen is closer to the actual treatment. UV exposure is one of the primary triggers that activates the hormonal-melanin pathway. Without daily, rigorous sunscreen use, no topical treatment will hold its results. Tinted sunscreens that also block visible light are preferred for melasma, because visible light, not just UV, has been shown to stimulate melanin production in people with the condition.
The patch on your skin carries its own history in its location, its edges, and when it appeared. Reading that history correctly, ideally with a dermatologist rather than a skincare algorithm, determines whether the next step forward is anti-inflammatory, hormonal, or purely protective.