PIH or PIE? Why Your Acne Marks Are Not Responding

The marks left behind by acne are not all the same substance. Brown marks are melanin and red marks are haemoglobin — two different chromophores in two different layers, requiring opposite treatment. The red ones are routinely lasered as though they were pigment, which is the single commonest reason a mark that should have faded in months is still there after two years.

Two Pigments Wearing The Same Name

When an inflamed lesion resolves, it can leave behind either of two things. Post-inflammatory hyperpigmentation is excess melanin, deposited in the epidermis, the dermis, or both, by melanocytes that were stimulated by the inflammation. Post-inflammatory erythema is not pigment at all — it is capillary dilatation and vessel damage in the papillary dermis, left behind by the same inflammatory process.

They look different once you know what to look for. PIH is brown, tan, grey-brown or slate depending on depth. PIE is pink, red, or in deeper-toned skin a dusky purple. But patients describe both as dark marks, and on a face carrying twenty of them in various stages, the two frequently sit side by side.

Neither is a scar. This distinction is worth making early, because it changes the entire prognosis. A scar is a change in tissue architecture — a depression, an elevation, a tether. A mark is a change in colour on skin that is still structurally normal. Run a fingertip across it with your eyes closed: if you feel nothing, it is a mark. The types of acne scar are a separate problem with a separate answer.

The Blanch Test Settles It In Seconds

Press a clear glass slide, or simply a fingertip, firmly onto the mark and watch what happens as you press. PIE blanches — the redness lightens or disappears under pressure because you have emptied the dilated capillaries producing it, and returns as soon as you release. PIH does not blanch, because melanin sitting in tissue does not move when compressed.

The test can be done at home with the flat edge of a phone screen and reasonable light, and it is more reliable than judging by colour alone. In Fitzpatrick type IV and V skin the two can appear deceptively similar — a deep PIE can read as brown-purple, and a superficial PIH can read as reddish-brown under warm indoor lighting.

Stretching the skin achieves the same thing by a different route. Pull the skin taut between two fingers: vascular marks fade as the vessels are flattened, pigmented marks stay exactly as they were. Patients who run both tests across their own face usually find they have both conditions simultaneously, in different regions.

Why PIE Is Routinely Mistreated

Red marks are described as pigmentation by patients, recorded as pigmentation on intake forms, and treated as pigmentation with pigment-directed lasers. A Q-switched or picosecond laser is tuned to be absorbed by melanin. Directed at a vascular lesion it is largely wasted energy — but it is not inert energy. It is heat, delivered into a dermis whose capillaries are already dilated and whose inflammatory cascade has not fully settled.

Heat provokes vasodilatation and can reactivate inflammation, which in turn recruits more melanocyte activity. The common outcome is a mark that is no lighter, sometimes redder for weeks, and which has now acquired a brown component it did not have before. The patient reasonably concludes that the laser was underpowered and a stronger setting is used, and the cycle repeats.

The same logic applies to aggressive resurfacing and heat-based facials on active or recently active acne. Inflammation is the thing driving both sequelae, and anything that adds to it prolongs both. Post-inflammatory erythema is often the condition that has been treated longest and improved least.

What PIH Is And How It Clears

Epidermal PIH sits in the keratinocytes of the upper layers and turns over with them — it fades on its own over months, faster with photoprotection and with topical agents that slow melanin transfer. Dermal PIH sits in melanophages below the basement membrane, has no turnover route available to it, and can persist for years without treatment.

Depth is what determines the timeline and the approach, and it is assessed rather than assumed. Lasering dermal pigment with settings intended for epidermal pigment achieves little. Treating epidermal pigment with unnecessarily aggressive settings risks producing more of the inflammation that caused the pigment in the first place — a particular concern in the skin types common in Singapore.

Consistent daily photoprotection is not an accessory to this treatment, it is most of it. Ultraviolet and visible light both stimulate melanocytes that are already primed, and a single unprotected weekend can undo a month of careful work. The full approach to post-inflammatory hyperpigmentation is built around that fact rather than around any one device.

What PIE Needs Instead

PIE needs a wavelength absorbed by haemoglobin rather than by melanin. A vascular laser coagulates the dilated capillaries selectively, leaving the surrounding tissue intact, and the redness resolves as those vessels are cleared and replaced. It is a different physical target and a different machine setting from anything used on pigment.

The second half of PIE management is controlling whatever is still inflaming the skin. Persistent erythema over a face with ongoing active lesions will keep being regenerated, and clearing it while new inflammation continues is treating the smoke rather than the fire. Effective acne treatment comes first in sequence, not after.

PIE also responds, more slowly, to time and to anything that reduces chronic low-grade inflammation in the skin — gentle barrier repair, avoiding heat, avoiding physical scrubs, and not picking. The instruction not to pick is not cosmetic advice. Each episode of manipulation restarts the inflammatory process that produced the mark, in the same spot, on skin that has not yet recovered from the last one.

When Both Are Present Together

Most faces carry both, and the mixture changes the sequence. Vascular work is generally done first, because clearing the erythema reveals how much genuine pigment is underneath — and because a red background makes accurate assessment of pigment depth harder for both patient and doctor.

Sessions are not combined casually. Stacking a vascular pass and a pigment pass in the same appointment doubles the thermal load on skin that is demonstrably prone to reacting to thermal load with more pigment. Spacing treatments is not commercial caution, it is the specific precaution that prevents the treatment from producing the condition it was booked to clear.

Where texture change is also present — a shallow depression, a visible tether, an icepick tract — that is a third problem again, and it does not respond to either approach. Colour and architecture are addressed separately, and the order matters. Acne scar treatment follows the clearance of active inflammation rather than preceding it.

Timelines And The Honest Answer

Epidermal PIH treated properly and protected properly improves steadily over months. Dermal PIH improves more slowly and to a lower ceiling. PIE treated with the correct wavelength clears reasonably well, though deep-seated erythema on the cheeks can be stubborn and may need a course rather than a session.

The honest limit is that none of this is fast, and no device shortens the biology. What treatment does is remove the obstacles — clearing the vessels, reducing the melanin load, and stopping the inflammation that keeps regenerating both. What it cannot do is compensate for sun exposure, ongoing active acne, or picking.

Anyone whose marks have not moved in two years of treatment should ask a single question at the next appointment: which of these marks blanch. If nobody has checked, the answer to why nothing has worked is probably in that test.