PIH is the footprint inflammation leaves in pigmented skin: a flat brown, grey or slate mark exactly where a pimple, bite, rash or overly aggressive treatment used to be. The insult is gone; the pigment it provoked remains. In Fitzpatrick III–V skin — most of Singapore — PIH routinely outlasts and outbothers the problem that caused it.
WhatsApp Dr Sin Yong →Inflammation is a megaphone aimed at melanocytes: cytokines released during any skin insult stimulate pigment production, and in darker skin types the response is brisk and generous. When the pigment stays in the epidermis, the mark is brown and fades as skin turns over. When inflammation disrupts the basement membrane, pigment drops into the dermis, where immune cells hold it — those marks read grey-slate and can sit for years [1]. Depth, not darkness, is what determines how long you will be looking at it — and depth is assessable in clinic.
Three different leftovers get called “acne marks”. A flat brown-grey mark is PIH — pigment. A flat pink-red mark that blanches under a pressed glass is post-inflammatory erythema — vessels, not pigment, treated on vascular principles like thread veins. A dent or dip you can feel is a true acne scar — a structural problem needing structural treatment. Mixing these up wastes months: pigment treatment does nothing for redness, and neither does anything for a dent. One examination sorts all three — and where active acne is still seeding new marks, the acne itself gets treated first, or the tail never ends.
The systematic reviews converge on a sequence [1,2]. First, stop the inflammation — active acne, eczema or picking makes PIH a moving target. Second, strict photoprotection: UV and visible light deepen existing marks, so tinted sunscreen is baseline treatment, not an accessory. Third, evidence-based lightening topicals — retinoids, azelaic acid, hydroquinone-class and newer agents under supervision. Fourth, where topicals plateau, conservative laser work: low-fluence pigment protocols such as laser toning and picosecond systems on the T2 platform — with the reviews of laser treatment in skin of colour emphasising restraint, because the same devices set aggressively cause the condition they treat [2]. The overlapping differential with other browns is covered in which brown is yours.
Scrubbing the marks — friction is inflammation, and inflammation is the disease. Lemon juice and DIY acids — chemical irritation on pigment-prone skin is a PIH recipe. Bleaching creams from unregulated sources — unsupervised strong agents can leave lasting damage including paradoxical darkening. Picking the next pimple — every squeezed lesion is a PIH order form. And impatience: dermal pigment clears on biology's schedule, and any clinic promising erasure in a fortnight is selling the calendar, not the outcome.
“In Singapore skin, the pimple is rarely the problem — the three-month brown souvenir it leaves is, and every squeeze places another order.”
— Dr Sin Yong
Epidermal (brown) marks typically fade over several months. Dermal (grey-slate) pigment can persist for years without treatment. Depth decides the timeline, and assessment reads the depth.
Melanocyte reactivity scales with constitutive pigment — Fitzpatrick III–V skin answers inflammation with more melanin, faster. It is biology, not fragility.
No — PIH is flat pigment; a scar is a texture change you can feel. They often coexist after acne, and each needs its own treatment plan.
Conservative, low-energy pigment protocols have supporting evidence — but aggressive settings cause PIH, so device restraint is the entire art in darker skin. This is a physician's-judgement treatment.
Yes — UV and visible light actively deepen existing PIH. Strict photoprotection is the difference between a mark that fades and one that entrenches.
Treatment-induced PIH — the inflammation from an aggressive procedure triggered the same pathway as a pimple. It usually fades, and it is precisely why settings are chosen conservatively for your skin type here.