When pico lasers leave pale spots
Picosecond Lasers and Hypopigmentation: Translating Histologic Insights Into Clinical Caution
Picosecond lasers are routinely described as the safe option for pigment. In a series of 796 patients treated for melasma, a small number developed pale spots that had not repigmented six months later — and the reason is not what most people assume.
Four numbers worth knowing
What we found
The pigment cells were still there.
Histology and electron microscopy showed melanocyte density preserved, with markedly reduced melanosome content. The cells had not been destroyed; they had stopped producing and delivering pigment. That is dysfunction, not depletion — and it is a different problem with different implications.
"Structurally preserved" is not the same as "safe".
Picosecond lasers are perceived as safer than nanosecond devices because of their shorter pulses and reduced heat spread, and the histology supports that at the level of individual cells. But preserving melanocyte structure does not guarantee pigmentary safety under cumulative exposure.
Melasma is where this matters, because of how melasma is treated.
Lentigines are treated with single passes over discrete spots. Melasma is treated with repeated low-fluence passes over broad areas, session after session. The ultrastructural evidence is most relevant precisely in that second pattern.
The clinical picture is confetti-like pale spots.
Pinpoint to speckled pale macules appearing within treated areas after repeated low-fluence treatments — well-demarcated focal lightening, confirmed on serial standardised photography.
Specific technique factors are implicated.
Treatment density and overlap, repeated passes over the same area within one session, slow hand speed causing pulse stacking, higher pulse repetition rates, and repeated treatment of the same anatomical site across sessions.
Photothermal effects occur even in a "photoacoustic" device.
Picosecond lasers are described as predominantly photoacoustic or photomechanical. In routine practice, with repeated pulses and cumulative treatments, clinically meaningful photothermal effects may still occur.
What this means for you
"Low risk" is not "no risk"
The reputation of pico lasers as uniformly low-risk may inadvertently obscure the importance of conservative technique and careful titration. Ask what density and how many passes, not just which machine.
Fewer passes, faster hand
Pulse stacking — overlapping pulses in the same spot because the handpiece moved slowly — is one of the implicated factors. It is a technique variable, not a device limitation.
Watch for early focal lightening
Early recognition of evolving hypopigmentation is what stops it progressing. Standardised photography between sessions is how you see it while it is still small.
Melasma deserves extra caution
Repeated low-fluence passes over a broad area is the exact exposure pattern these findings are about. Patients already prone to dyspigmentation carry more of this risk, not less.
Why this matters
Pigment lasers have improved steadily, and picosecond technology is a genuine advance — shorter pulses, less collateral heat, lower rates of the post-inflammatory darkening that used to follow Q-switched treatment.
That reputation has hardened into a belief that they are uniformly low-risk. This communication, written in response to a systematic review of the histology, argues that the ultrastructural evidence actually supports a more measured position: melanocytes can be left structurally intact and functionally impaired, and the pale spots that follow are the visible consequence of that.
The argument
Melanocyte survival is not the same as pigment safety. Counselling, conservative technique and early recognition of focal lightening remain the things that manage this risk — not the choice of device alone.
What this study cannot tell you
Every study has a boundary, and it is fairer to state it than to leave you to guess.
- The clinical figure comes from a single case series of 796 treated patients at one Australian centre.
- Three patients developed persistent hypopigmentation. Very small numbers, and the paper presents them as a signal rather than a rate to rely on.
- Follow-up was six months. Whether these spots eventually repigment over longer periods is not known.
- The link between the histological findings and the clinical hypopigmentation is a reasoned interpretation, not a demonstrated causal chain.
- This is a communication responding to a review, not original experimental work.
Questions people actually ask
Can laser treatment cause white spots?
Yes, though uncommonly. In a series of 796 melasma patients treated with picosecond laser, persistent pale spots occurred in 0.38% and had not repigmented at six months.
They appear as pinpoint to speckled pale marks within the treated area, typically after repeated low-fluence sessions rather than after a single treatment.
Are picosecond lasers safe for melasma?
They are widely used for melasma and generally well tolerated, with lower rates of post-inflammatory darkening than older Q-switched devices.
The caution this paper raises is about cumulative exposure: melasma is treated with repeated broad-area passes over many sessions, and that pattern of exposure is where the hypopigmentation risk appears to sit.
Does hypopigmentation after laser go away?
In the cases described here, it had not repigmented at six months. Longer-term outcomes are not known.
Because the melanocytes appear to survive but stop functioning, repigmentation is at least biologically plausible — but that is a mechanism, not a promise, and it should be treated as potentially permanent when you are consenting to treatment.
Cite this paper
Hang X, Lim DS. Picosecond Lasers and Hypopigmentation: Translating Histologic Insights Into Clinical Caution. Dermatologic Surgery. 2026. doi:10.1097/DSS.0000000000005097
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Published 2026 · Summary written and reviewed by Dr Davin Lim, FACD · General information, not personal medical advice.
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