Pico laser gone wrong:
PIH, hypopigmentation, rebound melasma and burns

Why does skin darken after pico laser, and when does it appear?

Skin darkens after pico laser because injured skin makes more melanin, and Fitzpatrick III to V skin makes it readily. A picosecond pulse fragments pigment mainly by a pressure effect, with less heat than a nanosecond pulse, but it is not heat-free: when fluence is too high for the skin, passes are repeated too soon, or sun reaches freshly treated skin, the epidermis is inflamed and melanocytes answer with pigment. The result is post-inflammatory hyperpigmentation, and the pico laser page lists it as the main risk of the treatment.

The darkening usually appears with a delay. Skin can look cleaner in the days after treatment and then darken over the following weeks, which is why a calm appearance the next morning does not mean the risk has passed, and why a test spot is read after that delay rather than straight away. The post-inflammatory hyperpigmentation page explains why the mark often outlasts the inflammation that caused it, and the guide to pico laser on Asian skin sets out why fluence, spot size, wavelength and interval matter more than the device.

Why do pale or mottled spots appear, and are they reversible?

Pale spots appear when melanocytes are depleted rather than merely inflamed. Repeated low-energy toning of the same area, visit after visit on an open-ended schedule, has been linked to punctate or confetti-like hypopigmentation, and a 2025 case series described hypopigmentation following picosecond laser treatment for melasma. The mechanism is cumulative: each pass removes a little pigment-producing capacity, and in melasma, where the surrounding skin is already unstable, the contrast shows.

Recovery is uncertain and cannot be promised. Some pale spots repigment slowly once treatment stops; in published reports others persist. That is the reason laser toning is not run on an open-ended schedule at this practice, and why the interval between visits and the decision to stop are set by reading the skin, not by a package count.

“Pigment already deposited is a deposit. Inflammation is what keeps producing it.”

Dr Sin YongOn the T2 Frax Radiance pico laser page

What is rebound melasma, and why does laser provoke it?

Rebound melasma is melasma that returns darker after a treatment that temporarily lightened it. Melasma is a chronic condition driven by hormones, vessels, visible light, heat and ultraviolet exposure, and heat is a trigger in its own right. A laser setting that clears a sun spot decisively deposits exactly the inflammation and warmth that melasma responds to, so the pigment can come back deeper and wider than before, often with post-inflammatory darkening added to it.

Rebound follows misdiagnosis as often as it follows dose. Melasma and sun spots look alike, and treating one as the other is the most common route to this outcome. Where laser has any role in melasma it is conservative, at low fluence and usually at 1064 nm, within a plan built on photoprotection and topical therapy; the melasma treatment page sets out that plan and why turning the energy up backfires.

How do burns, blisters and crusting go wrong?

Burns follow fluence that is too high for the skin, a small spot size concentrating energy near the surface, fractional mode run at aggressive settings, or any setting applied to tanned skin, which absorbs more energy than the operator planned for. Some crusting is expected: a treated sun spot darkens and forms a fine crust that flakes away on its own, and fractional mode leaves pinpoint redness and a rough texture while the skin renews.

The line between expected and wrong is crossed when blisters appear, crusts become thick, yellow or oozing, or pain, swelling and warmth increase instead of settling. Those signs point to a burn or an infection, and a burn in Fitzpatrick III to V skin carries its own risk of pigmentation or scarring as it heals. The article on pico laser downtime and side effects describes what each mode normally looks like afterwards, so that a departure from it is recognised early.

What does the assessment check before any pico laser is switched on?

The assessment identifies the pigment first. Dr Sin Yong examines the skin in appropriate light, with a dermatoscope where needed, and separates sun spots, freckles, post-inflammatory marks, melasma and dermal pigment, because each is treated differently and one of them is barely treated with laser at all. Any lesion that is changing, bleeding or unlike the others is referred for dermatological assessment before laser is considered.

The skin is then matched to the settings: Fitzpatrick type, recent sun exposure, photosensitising medicines and recent isotretinoin all change the wavelength, fluence and pacing, and a test spot is advised where the reaction is uncertain. Sun protection begins before the first visit. None of this removes the risks on this page; it is what makes them less likely.

When should you call, and what happens next?

Call the same day for blisters, thick yellow or oozing crusts, or pain, swelling or warmth that is increasing rather than settling. Dark or pale patches that appear weeks after treatment are not emergencies but should be reviewed rather than treated over, and strict sun protection matters in the meantime. The complication care page lists the signs that need same-day attention and what to do outside clinic hours.

What happens next follows a fixed order: stop adding energy, protect the skin from the sun, and reassess the pigment. Post-inflammatory darkening is usually managed with photoprotection and topical therapy and given time; a burn is treated to limit scarring; pale spots are observed with treatment stopped. If you were treated elsewhere, the assessment proceeds the same way, and what you are told is what is found on examination, not a verdict on the other clinic.