Post-inflammatory hyperpigmentation (PIH) is a flat brown, grey or slate mark left where a pimple, rash, bite or injury inflamed the skin. PIH treatment in Singapore follows an order: calm the inflammation, protect from UV and visible light, add lightening topicals under supervision, and consider low-fluence laser last. Dr Sin Yong assesses the depth of the pigment first.
What does post-inflammatory hyperpigmentation look like?
Why does the dark mark outlast the pimple?
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.
PIH, PIE, or a scar?
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.
Post-inflammatory hyperpigmentation on the body: legs, underarms and insect bites
Post-inflammatory hyperpigmentation on the body follows the same rule as on the face: inflammation came first, pigment followed. On the body the triggers are different, the skin renews more slowly, and the marks are easier to mistake for other conditions, so they are worth understanding on their own.
Common causes on the body
- Insect bites on the legs and arms, especially when scratched.
- Eczema in the elbow and knee folds, neck and wrists.
- Friction from bra lines, waistbands, inner thighs and underarms.
- Shaving, waxing and plucking, which can inflame hair follicles and leave dark dots.
- Acne on the back and chest, and minor burns, cuts and grazes.
Lookalikes a doctor rules out
- Acanthosis nigricans: velvety, thickened dark skin on the neck or in the armpits, linked with insulin resistance, so it prompts a check of blood sugar rather than a lightening cream.
- Fixed drug eruption: a round dusky patch that flares in the same place each time a particular medicine is taken.
- Pityriasis versicolor: a yeast infection causing fine, scaly patches that can be lighter or darker than the skin.
- Lichen planus pigmentosus: grey-brown patches, often in skin folds, reported more often in Asian skin.
What you can do at home, and what you cannot
Stop the trigger first: treat bites and eczema early so they are not scratched, wear loose, breathable clothing, and avoid harsh scrubs, loofahs and lemon juice. Use sunscreen on legs and arms that are exposed. What you should not do is buy body whitening creams of unknown content, because some contain undeclared strong agents; hydroquinone is a prescription medicine in Singapore. Grey-slate marks that sit deep in the dermis do not respond to anything applied at home.
In Asian skin
Fitzpatrick III to V skin answers inflammation with more pigment, and marks on the lower legs often last longer than marks on the face. Laser on the body is therefore used conservatively and only after the trigger is controlled.
See a doctor if the skin is velvety or thickened, a patch keeps returning in the same spot, patches are scaly or spreading, itching continues, or marks appeared after a laser or peel. Back and chest marks are covered under back acne treatment, and the pigment laser approach under pico laser for PIH.
What actually works for PIH?
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.
PIH treatment in Singapore: the order that avoids a second mark
PIH treatment in Singapore goes wrong most often through sequence, not through choice of product. The mark is the footprint of inflammation, so anything that inflames the skin again, from scrubbing to an aggressive laser, can add a mark rather than remove one. The four stages below are the order Dr Sin Yong works in, and each stage is only moved past when the one before it is in place.
The laser is the last step in PIH treatment, not the first, because the same device set aggressively causes the mark it is meant to clear.— Dr Sin Yong
| Stage | What is done | Why it comes here | Read more |
|---|---|---|---|
| 1. Barrier first | Stop the trigger: active acne is controlled medically, eczema is settled, picking stops, and scrubs and DIY acids are dropped | While inflammation continues, PIH is a moving target and every new lesion can leave another mark | Acne treatment |
| 2. Photoprotection | Daily broad-spectrum sunscreen, tinted where possible, with shade and hats | UV and visible light deepen existing marks, so protection is treatment, not an accessory | Which brown is yours |
| 3. Supervised topicals | Retinoids, azelaic acid, hydroquinone-class agents and newer lightening agents, prescribed and reviewed | They lighten epidermal pigment and suppress new pigment without adding inflammation when used correctly | Pigmentation guide |
| 4. Low-fluence laser | Where topicals plateau and the depth has been assessed: laser toning or picosecond settings on the T2 platform, conservative and reviewed | Last because the same devices set aggressively cause the condition they treat, particularly in darker skin | Pico laser for PIH |
Depth decides how far down the list a mark needs to go. Brown, sharper-edged epidermal PIH often clears with the first three stages. Grey-slate dermal PIH, where pigment has dropped through the basement membrane, is the one more likely to need conservative laser work, and it is also the one most easily made worse. That is why the assessment separates the two before any device is switched on, and why post-inflammatory erythema, which is red and blanches under pressed glass, is sent down a vascular route instead.
Darkening after a peel or laser elsewhere is treated as the same problem: the cause is reviewed, the barrier is restored, and the sequence starts again from stage one rather than repeating the treatment that caused it. The CO2 laser in Asian skin page and laser toning explain how energy settings are kept conservative in pigment-prone skin.
What doesn't work for PIH?
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
Laser for PIH: who should wait, and the risks
Laser has a place in post-inflammatory hyperpigmentation only after the inflammation has been controlled and topical treatment has been tried, because any heat or injury can add a new mark to skin that already darkens easily.
Who should wait: anyone with active acne, eczema or other inflammation in the area; a recent tan; pregnancy or breastfeeding; photosensitising medicines; recent isotretinoin, where the doctor advises on timing; a history of keloid scarring; and anyone whose dark marks have not yet been diagnosed, since melasma, Hori’s naevus and pigmented lesions can look similar.
Common and expected: brief redness and warmth; treated pigment can look darker before it flakes. The risks that matter: rebound darkening if the energy is too high or treatments are too close together; pale or mottled spots after frequent repeated toning; and, rarely, blistering or crusting. These risks are higher in darker skin and after sun exposure, which is why settings are conservative, intervals are set at review, and strict sun protection continues throughout.
Before any laser, tell the doctor about all creams and medicines, recent procedures and sun exposure. The pico approach to PIH is on pico laser for PIH.
Dr Sin Yong’s Viewpoint
In our skin, the pimple is rarely the real enemy — the three-month brown souvenir is. I spend more consult time on PIH than on the acne that caused it, and my first prescription is always the same: stop the picking, start the photoprotection, and let restraint do what aggression cannot. Every squeeze is an order form for another mark.
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