Key facts
- Mechanism
- Inflammation stimulates melanocytes; excess pigment stays in the epidermis or drops into the dermis
- Epidermal vs dermal
- Brown, sharper marks sit high and fade sooner; grey-slate marks sit deep and are slow to clear
- Who is prone
- Fitzpatrick III–V skin, where the melanocyte response to inflammation is brisk
- Typical causes
- Acne and picked spots, insect bites, eczema, friction, and mis-set lasers or aggressive peels
- Backbone of management
- Treat the cause, photoprotect strictly, then lightening topicals and, where needed, conservative laser
What PIH is, and why the mark outlasts the pimple
Any inflammation in the skin releases chemical signals that stimulate melanocytes, and in darker skin types the response is brisk and generous. When the extra pigment stays in the epidermis the mark is brown and fades as the skin turns over. When the inflammation disrupts the basement membrane, pigment drops into the dermis, where immune cells hold it; those marks read grey or slate and can persist for years. Depth, not darkness, is what decides how long a mark lasts, and depth can be assessed in clinic.
In Fitzpatrick III–V skin, which describes most of Singapore, PIH routinely outlasts and outbothers the problem that caused it. A pimple resolves in days; the mark it leaves can take months. The full condition page on post-inflammatory hyperpigmentation covers the biology and the evidence.
How PIH is managed in aesthetic medicine
The sequence matters more than any single product. First, the inflammation is stopped: active acne, eczema or picking makes PIH a moving target, which is why acne treatment comes before any work on the marks it leaves. Second, strict photoprotection, since ultraviolet and visible light deepen existing marks; a tinted sunscreen is baseline treatment, not an accessory.
Third, evidence-based lightening topicals such as azelaic acid, retinoids and hydroquinone-class agents, used under supervision because unsupervised strong agents can cause lasting damage, including paradoxical darkening. Fourth, where topicals plateau, conservative in-clinic work: low-fluence protocols such as laser toning or picosecond treatment, with settings chosen for the skin type, because the reviews of laser in skin of colour emphasise restraint for a reason.
“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 YongOn acne marks in Singapore skin
What PIH is often confused with
Three different leftovers are called acne marks. A flat brown or grey mark is PIH, which is pigment. A flat pink or red mark that blanches when a clear glass is pressed on it is post-inflammatory erythema, which is dilated blood vessels and is treated on vascular principles; brightening serums do nothing for it. A dent or dip that can be felt is a true acne scar, a structural problem that needs structural treatment. Mixing them up wastes months, and most acne-prone faces carry more than one.
PIH is also mistaken for melasma, which forms symmetrical soft-edged patches without a single insult behind them and is driven by hormones, light and heat; melasma relapses where PIH, once the inflammation stops, fades. Which brown is which is set out on the page on pigmentation types.
When a laser is not the answer
The same devices that treat PIH cause it when set aggressively. A peel or laser that is too strong for the skin type triggers the same pathway as a pimple, and treatment-induced PIH is a common reason patients present after sessions elsewhere. Heat is the problem, so in darker skin device restraint is the whole art, and a mark that darkened after a session calls for reassessment rather than more of the same setting.
A laser is also not the answer while the acne that is seeding new marks is still active, and it is no substitute for the habits that decide the outcome: no squeezing, no scrubbing, no lemon juice or DIY acids, and daily photoprotection. Dermal pigment clears on biology's schedule, and any clinic promising erasure in a fortnight is selling the calendar rather than the outcome.
