Red vs Dark Acne Marks: PIE and PIH Explained — Why the Colour Decides the Treatment

After a pimple heals, the skin often keeps a flat mark where it was. In lighter skin the mark tends to be red or pink; in medium to dark Asian skin it is more often brown, grey-brown or nearly black; many people have both. These are commonly called 'red acne scars' and 'dark acne scars', but neither is a scar — a scar is a change in contour — and, more importantly, they are not the same problem wearing two colours.

A red mark is post-inflammatory erythema (PIE): the inflammation of the pimple dilated and damaged the tiny blood vessels in the upper dermis, and they have not yet recovered. The colour you see is blood. A dark mark is post-inflammatory hyperpigmentation (PIH): the same inflammation stimulated melanocytes to overproduce melanin, which has been deposited in the epidermis and sometimes dropped into the dermis. The colour you see is pigment. Everything about treating them follows from that difference.

Press a clear glass slide — or simply a fingertip — firmly onto the mark for a second and look as you release. A red PIE mark blanches: the pressure empties the dilated vessels and the colour fades, then returns. A dark PIH mark does not change, because melanin does not move under pressure. Where a mark is purplish or brownish-red, it is often both, and you will see partial blanching.

Then check for contour. Stretch the skin gently in good side-lighting. If the colour disappears and the surface is smooth, it is a mark alone. If a dip or shadow remains after the colour fades, there is a scar beneath the mark, and the scar will need its own structural treatment regardless of what you do about the colour.

Because PIE is a blood-vessel problem, pigment-brightening products do little for it — a common frustration for people who buy 'dark spot' serums for red marks. What helps: time, since damaged capillaries recover over months; avoiding triggers that dilate vessels further (heat, hot showers, aggressive scrubbing, picking, alcohol); anti-inflammatory and barrier-repairing skincare (niacinamide, azelaic acid, centella); and, for persistent redness, vascular-targeted treatment at a clinic. Pulsed-dye and certain other vascular lasers target haemoglobin in the vessels; some pico and fractional devices also improve PIE indirectly by remodelling the upper dermis. Sunscreen still matters, because UV prolongs inflammation.

Retinoids help by thickening the dermis over time so vessels show less, but they can increase redness initially — introduce them slowly. Vitamin C is a reasonable supporting ingredient for both PIE and PIH. Give any topical routine three months.

PIH is a pigment problem, and the first treatment is prevention of more: daily broad-spectrum sunscreen (SPF 30 or above, reapplied), because UV directly stimulates the melanocytes that are already over-producing. Without it, every other step is undermined. Then brightening and turnover: retinoids to speed shedding of pigmented cells; azelaic acid, niacinamide, vitamin C, tranexamic acid and alpha-hydroxy acids to suppress pigment transfer and lift what is there. Over three to six months these fade epidermal PIH substantially in most people.

Where pigment has dropped into the dermis — typically the greyer, more stubborn marks on darker skin — topicals plateau, and this is where pico laser earns its place: picosecond pulses shatter melanin into fragments the body clears, with lower heat and lower risk of worsening the pigment than older lasers. Gentle chemical peels can help epidermal PIH. The one thing to avoid is aggressive treatment: strong peels, high-energy lasers or harsh home remedies on darker skin can produce new PIH on top of the old. Results vary by individual, and the goal is fading over months, not disappearance in weeks.

Most faces with post-acne marks carry a mixture: fresher red marks from recent lesions and older brown marks from earlier ones, sometimes with dents beneath. The sequence that works is to stop new lesions, protect from UV, run a brightening routine that also calms inflammation, and let time do what it will for the red marks. Then reassess at three months: persistent red marks may warrant vascular treatment; stubborn brown marks may warrant pico; any dents need structural treatment — subcision, resurfacing or TCA CROSS — planned separately from the colour.

DrPlus assesses post-acne marks and scars at the Johor Bahru clinic in Iskandar Puteri and at three Singapore clinics — Tanjong Pagar, East Coast and Novena. A doctor distinguishes PIE from PIH from scar under magnification, and the plan treats each on its own terms, with no obligation to proceed.