Darkening is not one diagnosis
PIH usually appears in the same area as an inflammatory injury and may become clearer as initial redness settles. It can be light brown, dark brown, grey-brown or patchy depending on pigment depth and skin tone. A doctor may need the timeline, photographs and examination to distinguish it from residual pigment that was never removed, a bruise, contact irritation, infection, treatment-pattern marks or melasma.
Do not immediately repeat the laser because the pigment “did not clear.” More inflammation can worsen some pigment problems, while a change of diagnosis may be more important than a higher setting.
Expected healing vs PIH
| Finding | Can occur in expected healing | Reason for review |
|---|---|---|
| Redness and warmth | Mild and steadily improving as the clinic explained | Increasing, sharply painful or spreading |
| Bronzing or tiny crusts | Can follow selected fractional or pigment protocols | Thick black eschar, open wound or pattern beyond what was explained |
| Brown/grey marks | May be PIH as inflammation settles | Rapid worsening, blistering or uncertain diagnosis |
| Swelling | Mild and trending down | Increasing, one-sided with severe pain, or involving the eye |
| Fluid, pus or fever | Not routine recovery | Prompt medical assessment for infection or another complication |
| Vision or neurological symptoms | Not routine recovery | Emergency care |
A clinic should give procedure-specific expectations. A generic “darkness is normal” is not enough if pain, blistering, discharge or a wound is getting worse.
What changes PIH risk
Fitzpatrick phototype describes how skin responds to ultraviolet exposure; it is not a complete measurement of ethnicity or PIH risk. People with darker phototypes often have more noticeable pigment responses, but recent tanning, melasma, previous PIH, active inflammation, eczema, acne, aggressive settings, treatment density, repeated passes, aftercare irritation and sun exposure also matter.
A randomized study of non-ablative fractional laser in phototypes IV–VI found self-limited PIH was common and occurred more often on higher-density treated sides. That does not mean one “safe density” applies across machines. It shows that treatment pattern—not just wavelength—can change risk.
Why the device name is not enough
A picosecond laser can be used with a focused or fractional optic for scars, or with other settings for pigment. A fractional CO₂ device is ablative; a fractional erbium device and non-ablative fractional laser create different injuries. Q-switched devices also vary by wavelength and target. Comparing only “Pico vs CO₂” misses energy, spot, density, pulse behavior, passes, endpoint and operator technique.
In a Thai split-face acne-scar trial, fractional 1064-nm picosecond treatment and fractional CO₂ produced comparable scar-volume improvement after a single session; mild PIH appeared on six of 25 CO₂-treated sides and none of the picosecond-treated sides in that protocol. It is useful comparative evidence, not proof that every Pico setting has zero PIH risk or that CO₂ is always unsuitable for Asian skin.
Before treatment
- Confirm the diagnosis: melasma, solar lentigines, PIH and acne scars need different plans
- Disclose previous PIH, keloid or hypertrophic scar, eczema, herpes and active acne
- List retinoids, photosensitising medicines, recent peels and other procedures
- Tell the doctor about recent tanning or unavoidable sun exposure
- Ask for the exact device, wavelength, handpiece or fractional optic and planned endpoint
- Ask how the plan changes for your pigment history—not simply your ethnicity
A test spot can provide information for selected treatments but cannot guarantee the response to a larger area, different density or repeated sessions.
General aftercare principles
Follow the treating doctor’s instructions for the exact procedure. In general, protecting a healing barrier means gentle cleansing, avoiding picking or scrubbing, and using sun protection that the treated skin can tolerate. Do not apply a strong acid, retinoid, bleach, steroid, essential oil or home peel because an online routine says it prevents PIH. Irritation itself can add inflammation.
Take photographs in similar lighting and note whether redness, pain, swelling and colour are improving. Contact the clinic before starting a new active ingredient. A treatment for established PIH is not automatically appropriate during the open-wound stage or for melasma.
When to contact a doctor
Contact the treating doctor promptly for worsening rather than improving pain, blisters, grey or black tissue, an open or draining wound, spreading redness, pus, fever, a cold-sore outbreak near the treated area, severe swelling or pigment that follows a sharply abnormal treatment pattern. Sudden visual change, eye pain, facial weakness, speech difficulty or another acute neurological symptom requires emergency care.
Even without an emergency, arrange review if darkening continues to spread, new pigment appears outside the treated area, or the clinic cannot explain whether the original diagnosis was pigment, melasma or a scar.
What prevention studies can tell us
A Thai randomized study of solar lentigines treated with a 532-nm Q-switched laser found that one topical ingredient used for two weeks before treatment reduced PIH incidence in the twice-daily study arm compared with no application. It studied 24 participants, one diagnosis, one laser protocol and one product regimen. It should not be copied as a universal prescription.
Other Asian split-face trials show that fractional picosecond devices can have less downtime or pigment change than selected ablative comparators while providing similar average scar improvement. These trials help with informed discussion, but device-specific results cannot replace a doctor’s settings and diagnosis.
The bottom line
Dark skin after laser may be expected bronzing, PIH, residual pigment, melasma, bruising or a complication. The trend and accompanying symptoms matter. Do not repeat treatment or start a bleaching regimen before the diagnosis is clear. Choose a doctor who records the exact device and settings, plans for your pigment history, and provides a route for prompt review if healing worsens.