Pico Toning Results: What Three Picosecond Laser Studies Actually Measured
Two time values sit inside the papers behind picotoning. One is a pulse width of 750 picoseconds. The other is the stress relaxation time of a melanin granule, 200 to 400 picoseconds. That the first number is longer than the second is where the explanation for picotoning starts.
Three papers cover the same broad category, but no two of them used the same equipment. One worked with a 1064nm Nd:YAG platform, another with a 755nm alexandrite, and a third with a 1064nm picosecond device paired with a 350-microsecond mode in the same session. “Picotoning” is a single word stretched over three different setups.
Where 750 picoseconds sits
The theory of selective photothermolysis holds that when exposure time is shorter than a target’s thermal relaxation time, heat destroys the target before it can spread to surrounding tissue. Papers working in the picosecond range describe something further: at this pulse width, the character of the tissue response changes. Photothermal effects recede and photomechanical effects take over, with plasma formation from optical breakdown and the resulting shockwave splitting tissue apart.
A histology paper states that 750 picoseconds is shorter than the thermal relaxation time of a melanosome, yet longer than the melanin granule’s stress relaxation time of 200 to 400 picoseconds. On that basis, it argues melanocyte damage may be lower. But the claim comes with a condition attached: it holds only when irradiation isn’t repeated often at an output high enough to cause intradermal hemorrhage.
The thermal relaxation time itself is never given in usable form. The parenthetical value attached to that sentence is 50 nanometers, a unit of length, not time. The 755nm paper does the same thing, describing its pulse as “much shorter than the melanosome’s thermal relaxation time” without ever supplying a number.
An experiment on necrosis that never matched its variables
An ex vivo model using abdominal skin from Korean women was irradiated three ways. A 755nm picosecond device used a 4.5mm spot at 1.26 J/cm². A 532nm Q-switched device used a 7mm spot at 1 J/cm². A 1064nm Q-switched device used a 7mm spot at 3 J/cm². Nitroblue tetrazolium staining four hours after irradiation showed less epidermal keratinocyte necrosis at the picosecond site than at the 532nm Q-switched site.
The three arms differ in wavelength, fluence, and spot size all at once. That the picosecond arm ran at a higher fluence than the 532nm arm and still produced less necrosis is stated plainly in the paper, but nothing in this design isolates which variable actually drove the difference.
Melanin was measured seven days later using Fontana-Masson staining, and it had decreased in both the 755nm picosecond group and the 1064nm Q-switched group. Which group decreased more, and by how much, is not given as a number.
The clinical portion covers three patients. All had Korean skin type IV and had stopped responding to low-fluence Q-switched toning. Two melasma patients received 6mm spots at 0.57 J/cm², for six and fourteen sessions respectively. One patient with post-inflammatory hyperpigmentation received a 2mm spot at 5.25 J/cm² for seven sessions, spaced two weeks apart. Over eight weeks of follow-up, no pigmentation occurred, and improvement was recorded only as descriptive grades of good and fair.
What one biopsy showed in the dermis
The volar forearm of a 61-year-old man was divided into three 20-square-centimeter zones. Each was treated with an 8mm spot at 10Hz, roughly 400 shots, 9 passes, at 0.7, 0.9, and 1.1 J/cm² respectively, over six sessions spaced two weeks apart. Two weeks after the final session, a 2mm punch biopsy was taken from the center of each zone.
Hematoxylin-eosin staining showed collagen fibers in the papillary dermis, previously fragmented, now appearing as continuous fine fibers. In the reticular dermis, thick collagen bundles had increased, and the fiber layer grew thicker as fluence rose.
Elastic fiber staining split by fluence level. At 0.7 J/cm² there was no difference from the control site. At 0.9 J/cm², elastin appeared in the papillary dermis. At 1.1 J/cm², thick elastic fibers branched toward the epidermis. Capillary proliferation was confirmed by hematoxylin-eosin staining at 0.7 and 0.9 J/cm². At 1.1 J/cm², the same stain showed nothing, and proliferation only became visible under elastic fiber staining.
Clinical assessment relied on the practitioner’s palpation and visual observation. Skin elasticity improved, more markedly at higher fluence, with no change in tone. The subject count is one, and the comparison is against that same person’s pre-treatment tissue.
The numbers from a trial that enrolled only poor responders
Between August 2018 and October 2019, 108 Central Military Hospital in Vietnam treated 20 women with skin type IV. All had dermal or mixed-type severe melasma. After at least eight sessions of 1064nm picotoning at four-week intervals, MASI fell from 16.24 to 15.12, a 7.44 percent decrease.
That 7.44 percent is both a result and an entry requirement. The study defined a poor responder as anyone whose MASI dropped less than 15 percent after eight sessions, and enrolled only patients who met that bar. It isn’t a figure that can be carried over as a general picotoning outcome.
Adding three more sessions that combined the same setup with a 350-microsecond mode in a single session brought MASI down to 9.77, a 35.15 percent drop from the prior measurement and 40.17 percent from baseline. The fractional pass used a PicoWay at 1064nm, 8mm spot, 0.6 to 0.8 J/cm². The mode that followed used a Clarity device at 15mm, 2.6 J/cm², with cooling switched off. The endpoint was a surface temperature of 40 to 42 degrees Celsius, which the paper cites as corresponding to a dermal temperature of 55 to 65 degrees.
The same paper notes that microsecond Nd:YAG doesn’t directly target melanosomes and hasn’t been shown effective for melasma on its own. There is no comparison group. The authors themselves consider it unlikely that picotoning alone produced a drop this large, while also calling for larger studies with objective measurement.
The sentences that set fluence and intervals
The histology paper’s recommendation is brief: irradiate once a month, or at a level that doesn’t cause intradermal hemorrhage, to avoid leukoderma. It notes that higher fluence may increase the effect, while still recommending a fluence that doesn’t draw blood.
The fractional condition in the same paper points the other way. A micro-lens array with 200 convex lenses raises the fluence at the skin’s surface to 2.5 times the value shown on the device. At 0.7 J/cm², the condition that produced clear intradermal hemorrhage, histologic improvement was better, and downtime followed accordingly.
The evidence on intervals is indirect. The recommendation the paper cites is simply not to repeat Q-switched treatment as often as weekly, or beyond five sessions up to ten. How long it takes for fragmented pigment to clear the skin isn’t given a number in any of the three papers. Collagen fiber half-life is reported at 15 years; elastic fiber half-life is listed as unknown.
When a number like 750 picoseconds or 40 percent comes up in a consultation, there’s one thing worth tracing back: which of the three papers it came from, and whether that paper’s device, wavelength, and fluence actually match the conditions being proposed.
Sources checked
- Histological investigation of picosecond laser-toning and fractional laser therapy
- Treatment of Melasma and Post-Inflammatory Hyperpigmentation by a Picosecond 755-nm Alexandrite Laser in Asian Patients
- Dual Toning Method with the Combination of Picosecond and Microsecond Nd:YAG in Refractory Melasma Unresponsive to Picosecond Alone
Scope — This article explains devices and technology. It does not provide individual diagnosis or treatment advice.