Just by the irradiation time becoming "a thousandth," the destructive power on spots and the gentleness on the skin change dramatically. "I went many times but the spots just won't disappear," "the laser made it worse instead"... Have you had such a painful experience? In fact,most people for whom Q-switched (the conventional laser) had no effect have a certain thing in common. In this article, we thoroughly explain the power of the latest pico laser along with research data.
[What you will learn from this article]
- The decisive difference in irradiation time between picoseconds and nanoseconds
- How to choose the 755 nm, 532 nm, and 1064 nm wavelengths
- The realistic number of treatment sessions based on research data
- Side-effect risks such as depigmentation and vitiligo
- Who is suited and who is not suited for a pico laser
Picoseconds vs. nanoseconds—why the irradiation time of the laser is important
The conventional Q-switched laser is irradiated in "nanoseconds (10⁻⁹ seconds: a billionth of a second)," while a pico laser is irradiated in even shorter "picoseconds (10⁻¹² seconds: a trillionth of a second)."The 3-order-of-magnitude difference between nanoseconds and picoseconds greatly changes the result of spot treatment.
The Q-switched laser mainly utilizes the "photothermal effect (thermal action)" and destroys the pigment of the spot with heat. On the other hand, because the pico laser's irradiation time is extremely short, thermal damage is small, and it generates a powerful shock wave called the "photoacoustic effect."
What people for whom Q-switched had no effect have in common—it is that large pigment particles like "rocks" that thermal destruction cannot break up remain in the skin. According to the study by Gang Ma et al. (2024, Plastic and Reconstructive Surgery), whereas the nanosecond laser leaves the pigment as clumps of 300–500 nm, the picosecond laser can pulverize it down to a "sand-like" extremely small size of 50–100 nm. The finely pulverized pigment comes to be smoothly excreted from the body by the body's immune cells (macrophages).
The effect on spots—which of 755 nm, 532 nm, and 1064 nm to choose?
In spot treatment, using the "wavelength" of the laser differently according to the cause and depth is the key to success.
- 755 nm (alexandrite): High absorption rate for melanin, optimal for shallow-layer spots such as senile pigment spots (common spots) and freckles.
- 532 nm (Nd:YAG): Like 755 nm, it reacts strongly to epidermal pigmented lesions.
- 1064 nm (Nd:YAG): Because the laser reaches deep into the skin, it is suited to treating deep-layer ADM (acquired dermal melanocytosis), nevus of Ota, and the like.
For those who wonder "will it really disappear?", we introduce concrete figures. In the comparative trial by Gang Ma et al. (2024, Plastic and Reconstructive Surgery), when the 755 nm wavelength was used, only23.3%achieved sufficient clearance (70% or more disappearance) with the nanosecond laser, whereas the picosecond laser recorded an overwhelming disappearance rate of73.3%.
Treatment sessions and intervals—the realistic guideline shown by papers
"The spot completely disappears with one laser session" tends to be expected, but the research data shows a more realistic guideline. In the paper by Gang Ma et al. (2024),a total of 5 treatments at 3-month intervalswere performed. As a result, those that "completely disappeared (100% cleared)" on the picosecond laser side were 10% of the total (0% on the nanosecond side). In other words,although 73.3% of people obtain a satisfying result, completely erasing it often requires multiple treatmentsin many cases.
The biggest factor for it not disappearing in one session is that the pigment of the spot extends to the deep layer, or that it takes time for the pulverized pigment to be carried out of the body by macrophages. To wait for the skin's turnover and excretion cycle, observing an interval of several months is recommended.
Side-effect risks—data on depigmentation, recurrence, and vitiligo
The pico laser is said to be gentle on the skin, but side effects are not zero. According to the data of Gang Ma et al. (2024), because picoseconds have less thermal damage than nanoseconds, it has been proven that the incidence of blisters (7.33% vs. 15.33%) and scabs (7.33% vs. 15.33%) is significantly lower.
However, because the shock wave is strong, there is also the unexpected data that"post-inflammatory hyperpigmentation (PIH)," the temporary darkening of spots after laser, occurs more with picoseconds (21.33% vs. 12%). In addition, the risk of "depigmentation (hypopigmentation)," in which color is lost like vitiligo, is also reported at 9.33% (4.67% for nanoseconds).
Furthermore, regarding the recurrence risk, according to the 2-year follow-up survey by Yanjun Zhou et al. (2024, Lasers in Surgery and Medicine), recurrence or worsening of spots (especially melasma) was seen in about 52.9%–58.8% of patients after treatment. Continuous care such as UV protection after laser is also indispensable.
Who is suited and who is not suited for a pico laser
From these data, the indications for a pico laser become visible.
- Who is suited: Those who want to erase common spots (senile pigment spots), freckles, ADM, or tattoos. It is especially recommended for those who treated with a Q-switched laser in the past but the effect plateaued because a large clump of pigment remained.
- Who is not suited / who needs caution: Those who have melasma (a hazy, symmetric spot). In the study by Yanjun Zhou et al. (2024, Lasers in Surgery and Medicine), it is shown that for melasma, Q-switched (1064 nm) has a higher short-term degree of improvement. Because the strong shock wave of the pico laser has the risk of stimulating melanocytes and causing reactive melanogenesis (PIH), melasma treatment requires a very careful output setting (pico toning, etc.).
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Summary
- The 3-order-of-magnitude difference in irradiation time: The pico laser finely pulverizes melanin into a sand-like form with "shock waves" rather than heat, so it is easily excreted.
- High effectiveness: The 755 nm pico laser boasts a high satisfaction (disappearance rate) of 73.3%, greatly surpassing Q-switched.
- The realistic number of sessions: It is not magic that perfectly erases in one session; in many cases multiple treatments at 3-month intervals (about 5 as a guideline, etc.) are needed.
- Understanding side effects: The risk of blisters from heat decreases, but because the risk of temporary pigmentation (PIH) from the shock wave exists, complacency is forbidden.
- Caution for melasma: For melasma, Q-switched is sometimes more suitable, and "discernment of the spot" by a specialist is more important than anything.
The optimal laser device and wavelength differ depending on the type of spot and skin quality. Whether your own spot is suited to a pico laser, or whether another treatment is better. Before worsening it with self-judgment, please feel free to consult us first.
References
- Yanjun Zhou, et al. (2023). An update on fractional picosecond laser treatment: histology and clinical applications. Lasers in Medical Science.
- Gang Ma, et al. (2024). 755-nm Picosecond vs. Nanosecond Alexandrite Lasers for Tattoo Removal: A Randomized, Split-Tattoo Clinical Trial. Plastic and Reconstructive Surgery.
- Yanjun Zhou, et al. (2024). Comparison of 755-nm picosecond alexandrite laser versus 1064-nm Q-switched Nd:YAG laser for melasma: A randomized, split-face controlled, 2-year follow-up study. Lasers in Surgery and Medicine.
The author of this article
Hiromitsu Nakamura Physician
Zetith Beauty Clinic Ginza / Osaka / Fukuoka
He has a track record of research presentations at domestic and international conferences in Japan and is also involved in technical guidance and education across the entire Zetith Beauty Clinic. Specializing in precise procedures based on anatomical grounds, he pursues natural results tailored to each individual's skin condition.