The clinical approach
PIH happens because inflammation revs up the melanocytes sitting in the basal layer of the epidermis. Those cells overproduce melanin, and depending on how deep the injury went, that pigment lands in the epidermis, drifts down into the dermis, or both. Where the pigment sits changes everything about how you treat it. Surface pigment responds faster. Dermal pigment is stubborn and slow.
The physics behind selective treatment was described by Anderson and Parrish in 1983, the theory of selective photothermolysis. Pick a wavelength the target absorbs more strongly than surrounding tissue, deliver it in a pulse short enough that the heat stays put, and you damage the pigment while sparing the skin around it. Melanin absorbs across a wide band, and the 1064nm wavelength of a Q-switched Nd:YAG penetrates deep with relatively low melanin absorption up top. That last part matters. In darker skin, a wavelength the epidermis grabs too eagerly can cook the very cells you're trying to calm, and you get more PIH, not less.
So the logic runs backward from most pigment work. You're not chasing the fastest clearance. You pick parameters gentle enough to never re-injure the skin: low fluence, larger spot, generous cooling, letting a series of light passes do slowly what one hot pass would ruin.
Treatment protocol
A realistic PIH course is patient. Plan for four to eight sessions spaced roughly three to four weeks apart, and tell the patient upfront that dermal pigment may need more. Before any device touches skin, the underlying inflammation has to be under control. Treating active acne while the breakouts keep coming just feeds new pigment into the same spots. A sensible sequence:
- Confirm the trigger has settled and the marks are stable, not actively spreading.
- Do a test spot, especially on Fitzpatrick IV to VI skin, and watch how it reacts over a week or two.
- Start low. A low-fluence, large-spot Q-switched pass is safer than an aggressive setting that risks a fresh burn.
- Pair the device with daily broad-spectrum sunscreen and, where appropriate, a topical such as hydroquinone under practitioner guidance.
Aftercare is mostly about sun. UV exposure is the fastest way to undo your progress and darken PIH again, so strict photoprotection isn't optional. Expect gradual lightening across the series, not a dramatic before-and-after. One caution worth repeating: darker skin carries a real risk of paradoxical darkening from over-treatment, so when you're unsure, dial down and add a session instead of pushing power. This is professional equipment for trained operators who can read skin response.
Recommended equipment
For PIH the workhorse is the Q-switched Nd:YAG. Our QN-03 Q-Switched Nd:YAG delivers the 1064nm wavelength that reaches pigment at depth while keeping upper-layer melanin absorption modest, which is what you want when you're treating skin that scars easily. Its short nanosecond pulses target pigment without dumping heat into surrounding tissue, and a frequency-doubled 532nm option covers the more superficial marks.
Where you need finer control, the QE-01 EO Q-Switched Nd:YAG uses electro-optic switching for a stable pulse, keeping every pass predictable across a long series. Consistency is a safety feature here, not a luxury. If a patient's pigment overlaps with a mixed condition like melasma, the same low-and-slow discipline applies. Match the platform to your typical patient skin types and case mix.
Frequently asked questions
Will laser treatment cure my PIH completely?
No honest clinic will promise a cure. Energy-based treatment helps fade the pigment and can speed up an otherwise slow natural process, but results vary with how deep the pigment sits and your skin type. Epidermal marks tend to clear well. Dermal pigment is slower and may only partly resolve. Sun protection during and after strongly affects the outcome.
Is it safe for darker skin tones?
It can be, with the right settings and an experienced operator. Darker skin holds more active melanocytes, so aggressive energy can trigger fresh pigment instead of clearing it. That's why we favor a 1064nm wavelength, low fluence, a test spot first, and extra sessions over higher power. Choosing the wrong parameters is the main risk, and it's an avoidable one.
How many sessions will I need?
Most people need between four and eight sessions, spaced about three to four weeks apart. Stubborn dermal pigment can take more. Your practitioner judges the pace by how your skin responds, and rushing the interval doesn't speed the result, it just raises the risk.
Can I treat PIH while my acne is still active?
Better not to. If the inflammation that caused the marks is still flaring, treatment chases pigment that keeps regenerating. Getting the acne under control first gives you a stable target and a cleaner result. Your clinician may combine pigment work with an acne plan once the breakouts calm down.