Pico laser for dark skin:
the fluence logic, and when to say no

Why does fluence matter more than the device on dark skin?

Fluence is the energy delivered per unit area of skin, and it is the setting that most directly decides how much heat a pulse leaves behind. A picosecond laser earns its reputation on dark skin because its pulse is short enough that a pigment particle is fragmented mainly by a pressure effect before much heat spreads into the surrounding tissue. That is a property of the pulse, not a licence for the energy: raise the fluence far enough and the epidermis, which in Fitzpatrick IV to VI skin holds a great deal of melanin, absorbs enough of the pulse to inflame, and inflammation is the signal that drives post-inflammatory hyperpigmentation. The margin between clearing a sun spot and darkening the skin around it is narrower in darker skin, and fluence is the dial that moves across it.

The published series show both sides. A retrospective review in the Journal of the American Academy of Dermatology of a picosecond laser with a diffractive lens array in Fitzpatrick IV to VI skin found it workable at the settings used, with a low rate of pigment change. A retrospective analysis of a 755 nm picosecond laser for pigmented lesions in Asian patients recorded post-inflammatory hyperpigmentation in a proportion of them, and a later Asian series with a dual-wavelength picosecond laser reported transient darkening at some settings. The device was the same category in each; the fluence, wavelength, spot size and interval were what differed. No figure is quoted on this page because the right one depends on the pigment, its depth, the phototype and the skin's own history, and is set by Dr Sin Yong for the face in front of him.

Which wavelength and mode are used for darker skin?

Wavelength sets how strongly melanin absorbs the light and how deep it travels. At 532 nm absorption is strong and shallow, which clears a superficial freckle decisively in fair skin and heats the epidermis in dark skin; 1064 nm is absorbed far less by epidermal melanin and travels deeper, which makes it the conservative choice for Fitzpatrick IV to VI and for pigment that has dropped into the dermis; 785 nm sits between the two. On the DEKA TORO used for Dr Sin Yong's T2 Frax Radiance protocol, the 785 nm picosecond emission and the 1064 nm nanosecond emission are the darker-skin tools, and 532 nm is reserved for superficial pigment in lighter skin.

Mode matters as much. Low-energy toning passes a larger spot across a field at gentle fluence and is how diffuse pigment and post-inflammatory marks are approached in darker skin; high-energy spot treatment of a single sun spot delivers more heat to a small area and is used sparingly and after a test. Fractional delivery, in which a diffractive optic creates small zones of tissue breakdown with intact skin between them, is a different exposure again and is run at conservative density. A larger spot size lets the beam reach deeper before it scatters and spreads the energy over more skin; a smaller spot concentrates it near the surface. The pico laser for PIH page applies this logic to a mark that exists because the skin already over-reacted once.

“On dark skin I set the fluence for the skin first and the spot second. A pico pulse buys me margin. It does not buy me permission to be aggressive.”

Dr Sin YongOn picosecond settings in Fitzpatrick IV to VI skin

How is PIH prevented before, during and after pico laser on dark skin?

Before: no tan. A recent tan or sunburn means more active melanocytes, so treatment is deferred until it has fully faded, and daily broad-spectrum sunscreen starts before the first visit rather than after it. Active acne, eczema or any inflamed area in the field is settled first, because new marks would replace treated ones. Exfoliating acids and retinoids are paused if advised. The skin's history is taken: darkening after any earlier laser, peel or injury predicts the reaction and lowers the starting fluence. Where the reaction is uncertain, a small test patch is treated and read after the delay in which darkening appears, which is a delay of some length rather than overnight; a patch that looks calm the next morning has told the doctor little.

During: the longer wavelength, a low fluence, a larger spot and toning across a field rather than high-energy spots, with the endpoint read on the skin rather than taken from a chart. After: sun protection every morning and reapplied outdoors, shade in the middle of the day, no picking at a darkened spot while it sheds, bland skincare until the skin settles, and a long interval before the next pass. The stop rule is part of the plan: an area that darkens after a treatment is reviewed and rested, not treated again, because a second pass on inflamed skin adds the very signal that caused it. Toning is not run on an open-ended schedule, because frequent repeated toning of the same area is linked to pale mottled spots, which in darker skin are more visible than the pigment they replaced. The pico laser on Asian skin article lists the questions worth asking any clinic.

Why is melasma on dark skin treated with particular caution?

Melasma is common in Fitzpatrick IV to VI skin, is often mistaken for sun spots on the cheeks, and is a chronic condition with hormonal, vascular and ultraviolet drivers that heat provokes. A fluence that clears a sun spot can leave melasma darker, and in darker skin that rebound is harder to reverse. Where a laser has a role it is conservative: low-fluence 1064 nm toning as one component of a plan built on photoprotection, including tinted sunscreens with iron oxides for visible light, and topical therapy, with the melasma treatment page setting out the full sequence and the pico laser for melasma page explaining when it helps and when it worsens.

Telling melasma from a sun spot, from post-inflammatory hyperpigmentation and from Hori's naevus, which is dermal and sits in the same place, is the first step, and it is done by history, distribution and examination in appropriate light rather than by trying a laser and seeing. The pigment can be reduced, but the mechanism producing it continues, which is why melasma tends to return and why a plan that is only laser fails in darker skin more visibly than in lighter.

Who should not have pico laser on dark skin, and how does Dr Sin Yong plan it?

Some people should wait and some should be directed elsewhere. Recently tanned or sunburnt skin waits until the tan has faded. Active acne, eczema, infection or a cold sore in the field is treated first. Photosensitising medicines and recent isotretinoin are discussed before any pulse. Pregnancy is a reason to defer. A keloid tendency calls for caution with fractional mode. Anyone whose skin darkened badly after a previous laser is treated, if at all, from a test patch at a lower starting point. A mark that is changing, bleeding or irregular is examined and may be referred to a dermatologist rather than lasered. Melasma is not treated as a sun spot, and a red mark, which is vessels rather than pigment, is not a picosecond target at all; the pressing-glass test on the PIE page separates the two.

Dr Sin Yong performs every pico laser treatment himself after examining the skin in appropriate light, with a dermatoscope where needed. In darker skin he starts from the wavelength the epidermis absorbs least, a low fluence and toning mode, uses a test patch where the reaction is uncertain, spaces visits so that the pigment response can be read before the next step, and stops if an area darkens. What decides the plan is the pigment and its depth, the phototype and the skin's own history of darkening, whether melasma or inflammation is present, and the sun the skin sees between visits. Aftercare is explained on the day and follows the pattern above: sun protection, no picking, bland skincare, a long interval and a review timed to when darkening would appear. Fees follow the plan and are set out in writing after assessment, as explained on how fees are quoted.