Picosecond lasers, with a pulse duration of 10–12 seconds, are considered a fast and effective method for tattoo removal because most tattoo pigment size ranges from 30 to 300 nm with short thermal relaxation time (< 10 ns) [7]. Therefore, a picosecond laser can provide greater thermal stress in targeted tattoos [8]. In addition to photoacoustic effects within targeted tattoos leading to the mechanical dissolution of the ink particles, an endothermic steam carbon reaction occurs, which changes the properties of inks, reducing their visibility [9, 10]. Furthermore, picosecond technology could permit lower fluences to be delivered, which theoretically lower the risk of adverse effect [11].

In a study by Park et al. 2021, they included only nine patients for tattoo removal in their study (using picosecond Nd: YAG laser). They reported that the mean clearance was 86.6% after receiving 6–8 sessions with 4–8 weeks in-between, they used fluence 2.5–4.8 j/cm2, repetition rate 6–10 Hz). This was in accordance with the current study with more patients (20 patients) and better results (we reported that 40% of patients showed excellent improvement, the mean of clearance was 61 ± 24.6) with only two sessions 8 weeks apart [12].

Ross et al. were the first to report the better effect of the picosecond laser comparing nanosecond laser in human patients using a 1,064-nm Nd: YAG laser with a pulse duration of either 35 picoseconds or 10 nanoseconds. The parameters included a fluence of 0.65 J/cm2 and a spot size of 1.4 mm [4]. Choi et al. compared picosecond and nanosecond lasers in their ability to remove multi-colored tattoos using Hartley guinea pig. They first compared a nanosecond quality-switched Nd: YAG laser with picosecond alexandrite and quality-switched Nd: YAG lasers and then the picosecond quality-switched Nd: YAG laser with the picosecond alexandrite laser and concluded that picosecond lasers are more effective and safer than nanosecond laser [14].

Adverse effects of pico-laser included pain, swelling, and blistering, but resolved within a few days. Also, hyperpigmentation or hypopigmentation can occur, as reported as 20% of hypopigmentation and 13% of hyperpigmentation in a previous study using picosecond alexandrite laser [15]. In the present study, pain, erythema, petechiae, and swelling were the only reported side effects which resolved within one to three days.

The main mechanism of picosecond laser tattoo removal involves the fragmentation of the chromophore through both photothermal and photoacoustic effects. Picosecond lasers transmit light pulse lengths that are closer to the TRT of tattoo pigment molecules; therefore, they can deliver heat radiation more efficiently and can be destructively focused on the target area. For example, the average size of carbon black in Indian ink is approximately 40 nm in diameter, while the TRT for 40 nm particles is approximately one nanosecond. The picosecond pulse can be thermally confined to the target because it is irradiated with a pulse duration of less than 1 nanosecond [14].

Bennardo et al. conducted their study on 34 patients, The patients received seven sessions (mean 3.3 + 2.0 sessions), more sessions were done for the professional admixed colored tattoos in extremities while facial tattoos and one colored black tattoo responded to fewer sessions, the sessions were done with 8 weeks interval, they reported over 40% of patients showing complete removal (80–100%) of tattoos and the rest were with 60–80% removal. No severe side effects were reported. No patients left the study. In three cases, a final “ghost effect” was reported; six participants developed petechiae after treatment and were medicated with an occlusive dressing, hydrolytic enzymes, and antibiotics, with the disappearance of the vascular manifestations in one to two weeks [16]. This was in agreement with the current study but without the ghost effect.

Picosecond pulses seem to guarantee higher effectiveness than longer nanosecond pulses, thus reducing the number of treatment sessions and improving cosmetic outcomes. The picosecond Nd: YAG laser is reported as the optimal tattoo removal device because it can obtain excellent cosmetic results with minimal skin damage, low scarring risk, and lower incidence of hypopigmentation than the picosecond alexandrite which causes more side effects. A two-month interval between sessions permits the removal of tattoo-pigmented particles via the phagocytic cells, and it is necessary before carrying out any other session or procedure. The results, however, may not be always cosmetically acceptable [18, 19]. However, these results may be biased because picosecond sources are often used for harder-to-treat tattoos, such as professional tattoos with mixed colors [16].