The prevalence of tattoos has increased in recent years, but tattooed individuals are still negatively stigmatized as being less inhibited, competent, sociable, and more sexually promiscuous [1]. Therefore, an increasing number of patients are seeking effective tattoo removal [2]. Historically, the removal of undesired tattoos included destructive techniques, such as dermabrasion, chemical destruction, and surgery; however, significant scarring and residual pigmentation have led to their discontinuation [3,4]. Since 1966 when a ruby laser was first introduced as a safer and more effective tattoo removing modality, laser has become the cornerstone of tattoo treatment [5]. The basic principle of tattoo removal with a laser is selective photothermolysis: when a chromophore is heated for less than its thermal relaxation time (TRT), chromophore destruction without damage to the surroundings will occur. The size of tattoo ink particle varies from 30 to 300 nm, corresponding to about 10 ns (10^–9 s) of TRT. Therefore, lasers with pulses of nanoseconds or shorter are required for optimal tattoo clearing [5]. Currently, picosecond (10^–12 s) lasers are increasingly replacing conventional Q-switched nanosecond lasers and have been developed at wavelengths of 532, 730, 755, 785, and 1,064 nm, all of which have been reported to be effective at clearing almost every color of tattoo ink, as well as paradoxically darkening the tattoo [6].

Multiple treatment sessions are necessary to achieve satisfactory tattoo lightening: 5-10 treatments for amateur tattoos and up to 25 sessions for professional tattoos [3,7]. Conventional therapy involves a single laser pass every month, making it lengthy, expensive, and impractical, and causing patient frustration and desertion [7,8]. Multiple passes per session fade tattoos better than single passes, although this is impeded by immediate whitening owing to thermally induced cavitation bubbles. Using topical perfluorodecalin (PFD) after each pass (the R0 method), cutaneous whitening resolved within 5 seconds, reducing the total treatment time to 5 minutes and effectively removing tattoos [8].

Previous studies evaluating the efficacy of R0 technique on tattoo treatment has been conducted using nanosecond lasers, whereas studies on picosecond lasers are still lacking. In this study, we aimed to evaluate the efficacy and effectiveness of the R0 method for tattoo removal in Korean patients.

We conducted a retrospective chart review of Korean patients who underwent laser tattoo removal at the Yonsei Star Skin and Laser Clinic in Seoul, Republic of Korea from January, 2021 to July, 2022. The exclusion criteria included a history of keloid or hypertrophic scars, skin infection around the tattoo area, pregnancy, lactation, history of previous laser treatment, dermabrasion, chemical peeling of the tattooed skin, or any photosensitivity medication history.

Before the laser procedure, 9.6% topical lidocaine (SM Cream 9.6%; CellBion Co., Ltd.) was applied to all tattoos for 30 minutes with occlusion. The ointment was washed off with soap and water, and the target area was prepped with alcohol swap before the procedure. Both patients and physicians wore protective eyewear throughout the treatment session. All patients were treated with picosecond Nd:YAG laser (PicoWay) at wavelengths of 532, 730, 785, and 1,064 nm at each session, with spot size 3-5 mm and fluence ranging from 1.0 to 3.4 J/cm² until the whitening was observed. All tattoos were treated with medical-grade topical sterile PFD (DESCRIBE^® PFD Patch; Merz North America) after each pass. Four laser passes were performed on each treatment session, and a total of 4 treatments at 4-week interval were done. All adverse events, such as blisters, crusting, pain, pinpoint hemorrhage, dyspigmentation, and local allergic reactions, were recorded throughout all treatment sessions. Immediately after each session, ice bag was applied to the treatment site for 10 minutes and occlusive dressing was done after applying antibiotic ointments. We instructed all patients to avoid direct sun exposure and use sunscreen during the treatment duration.

Two dermatologists who were not involved in the study examined each tattoo using photographs taken before the first and final treatment sessions. The following parameters were used to evaluate treatment response: 0%-9% clearance as grade 0-1 (no response), 10%-34% clearance as grade 2-3 (poor response), 35%-69% clearance as grade 4-7 (fair response), 70%-90% clearance as grade 8-9 (good response), and >90% clearance as grade 10 (excellent response).

Twenty Korean patients with twenty tattoos were included in this study. Fifteen females (75%) and 5 males (25%) were treated using the R0 method, and their ages ranged from 17 to 53 years (mean age, 30.7 years). Most patients were categorized as having Fitzpatrick skin type III or IV. Of the 20 tattoos, 17 (85%) were multicolored, with black and blue being the most common ink colors (14 tattoos, 70%); only three tattoos were single-colored (two black tattoos and one skyblue tattoo). The specific information for each patient is presented in Table 1, and specific laser parameters used on each treatment session are presented in Table 2.

Table 1 . Specific demographics of each patient

Patient	Sex	Age (yr)	Fitzpatrick skin type	Location	Color
1	Male	25	III	Flank	Black, blue
2	Male	45	IV	Posterior neck	Black, blue
3	Female	53	IV	Arm	Black, blue
4	Female	23	IV	Lateral neck	Black, blue
5	Female	25	III	Chest	Black, blue
6	Female	30	IV	Posterior neck	Black, blue
7	Male	17	IV	Dorsum of hand	Black, blue
8	Female	28	IV	Wrist	Black, blue
9	Female	24	IV	Arm	Black, blue, red
10	Female	37	III	Arm	Black, blue, white
11	Female	25	IV	Arm	Black, blue
12	Female	33	IV	Ankle	Black, blue
13	Female	24	IV	Lateral neck	Skyblue
14	Male	30	IV	Arm	Black, blue
15	Female	31	IV	Earlobe	Black, blue
16	Male	29	IV	Arm	Blue, skyblue
17	Female	34	IV	Arm	Black
18	Female	52	IV	Arm	Black, blue
19	Female	20	IV	Arm	Black
20	Female	29	IV	Wrist	Black, blue

Table 2 . Specific laser parameters used on each treatment session

Patient	Wavelength (nm)	Fluence (J/cm2)
		Session 1	Session 2	Session 3	Session 4
1	1,064	1.4-1.8	1.8	2.0	2.0
2	1,064	1.8-2.4	2.2	3.2	3.2
3	1,064	1.8	2.8	2.8	3.4
4	1,064	2.0	2.4	2.4	2.4-2.8
5	1,064	1.2	2.0	2.0	2.4
6	1,064	1.2-2.6	1.4-2.6	1.4-3.4	3.4
7	1,064	1.9-2.2	2.4	3.4	3.4
8	1,064	1.6-2.0	2.0-2.4	3.1	3.4
9	1,064	1.6	1.6	3.1	3.4
10	1,064	1.2-2.2	1.2-2.2	1.4-2.2	1.9-2.4
11	1,064	1.2-1.6	2.0-2.4	3.4	3.1-3.4
12	1,064	1.9-2.5	3.1-3.4	3.4	2.4
13	730	1.4	1.4-1.7	1.7	1.7
14	1,064	1.6-2.2	2.0-2.4	2.4-3.0	3.0-3.4
15	1,064	2.0	2.4	3.0	3.4
16	1,064	2.0	2.5-2.8	2.8	3.0
17	1,064	1.4-2.4	2.0-2.4	2.5-3.1	3.4
18	1,064	1.9-3.1	2.4-3.2	3.2	3.4
19	1,064	1.0-2.2	1.0-1.8	1.4-2.4	2.2-2.8
20	1,064	1.2-1.6	1.4	1.8-2.2	2.6

Both dermatologists evaluated all patients as having either a good or excellent response (Figs. 1-3): dermatologist A graded 4 patients (20%) as having a good response and 16 patients (80%) as having an excellent response; dermatologist B graded 14 patients (70%) as having a good response and 6 patients (30%) as having an excellent response (Table 3). Hyperpigmentation and blister formation have been reported; however, these side effects resolve spontaneously before the final treatment. No other long-term adverse effects were observed after the final treatment session.

Table 3 . Treatment response of each patient after the last session

Patient	Dermatologist
	A	B
1	9	8
2	10	10
3	10	9
4	10	9
5	10	10
6	9	8
7	8	8
8	10	9
9	10	8
10	10	9
11	10	9
12	10	10
13	10	10
14	10	9
15	10	10
16	10	8
17	10	8
18	10	10
19	9	8
20	10	9

0%-9% clearing is defined as grade 0-1 (no response); 10%-34% clearing is defined as grade 2-3 (poor response); 35%-69% clearing is defined as grade 4-7 (fair response); 70%-90% clearing is defined as grade 8-9 (good response); and more than 90% clearing is defined as grade 10 (excellent response).

Figure 1. Clinical photographs of a 37-year-old female patient with a tattoo on right arm (patient 10). (A) Before the laser treatment. (B) After 4 treatment sessions. Both dermatologists rated as having more than 70% clearance (dermatologist A rated as 10 and B rated as 9).

Figure 2. Clinical photographs of a 31-year-old female patient with a tattoo on right earlobe (patient 15). (A) Before the laser treatment. (B) Both dermatologists graded as having an excellent response (10) after 4 treatment sessions.

Figure 3. Clinical photographs of a 29-year-old male patient with a tattoo on right arm (patient 16). (A) Before the laser treatment. (B) After 4 treatment sessions, the tattoo almost faded away, and both dermatologists evaluated as having more than 70% response (dermatologist A rated as 10 and B rated as 8).

Effective tattoo removal involves three broad aspects: the laser(s) used, skin phenotype, and tattoo-dependent factors such as the type, depth, and size of the tattoo. A substantial part of tattoo-removal research is directed towards modulating laser parameters to maximize results [3].

Most tattoo particles have a diameter of 100 nm with a TRT of less than 10 ns. Thus, theoretically, picosecond lasers are expected to be superior to nanosecond lasers in terms of tattoo clearance because of greater temperature-induced changes [3,5]. In 1998, Ross et al. [9] treated the same tattoos with 35-picosecond and 10-nanosecond Nd:YAG lasers and proved that picosecond pulses were more effective than nanosecond pulses in clearing black tattoos. Since then, many other studies have proved effective clearance with picosecond lasers, especially in blue-black tattoos, but also with more resistant pigments such as blue, green, red and yellow [10]. Bernstein et al. [4] effectively treated 36 multicolored tattoos with picosecond-domain Nd:YAG lasers, achieving an average removal of 79% after an average of 6.5 treatments. Brauer et al. [11] successfully treated 12 tattoos containing blue and/or green pigments with picosecond 755-nm alexandrite lasers, demonstrating at least 75% clearance after one or two treatments.

Conventional laser tattoo removal involves a single pass, owing to whitening immediately after treatment. This is due to the interaction of the laser with the tattoo pigment; ink particles transmit energy from the lasers to the surrounding tissue, resulting in the production of small cavitation bubbles that appear as an opaque white layer. This optical scattering prevents lasers from effectively penetrating and interacting with the pigment [7,12]. The R20 method, whereby a patient waits for 20 minutes for whitening to fade between each pass, enables multiple passes in one treatment session [7]. However, this method is clinically impractical and carries the risk of increased epidermal injury [7,12]. PFD, a liquid fluorocarbon, has a high gas solubility and acts as an optical clearing agent. Previous in vitro experiments have shown that infrared laser radiation in an aqueous environment produces water vapor bubbles, inducing a pressure gradient between the treated surface and the PFD. Water bubbles then rise from the treatment surface toward the PFD, enhancing the optical clarity [8]. Reddy et al. [8] also proved that hyper-reflective bubbles disappear after 10 minutes of PFD application but at 20 minutes without intervention in optical coherence tomography imaging. Thus, the PFD enables multiple passes per session (R0 method), making laser tattoo treatment faster and more efficient.

Previous research has shown that the combination of PFD and picosecond lasers is excellent for tattoo removal. Vangipuram et al. [12] proved the effectiveness and safety of PFD patches and liquid PFD in combination with picosecond- and Q-switched Nd:YAG lasers for treating tattoos containing blue, black, red, green, purple, and pink ink. Feng et al. [13] studied 45 patients who received picosecond laser tattoo treatment with PFD patches. All treatments were well tolerated, safe, and effective; adverse events such as dyspigmentation, scarring, and textural changes were not observed, and no patient discontinued treatment due to discomfort. Moustafa et al. [14] used 532 nm and 1,064 nm picosecond Nd:YAG lasers and PFD patches to treat cosmetic eyebrow tattoos. All patients achieved 75%-100% clearance after 1-3 sessions without any significant adverse events.

In this study, four treatment sessions at 4-week intervals were conducted, and the same treatment response parameters were used as in the Ross et al. [9]’s study. All patients responded well to treatment, and only temporary blistering and hyperpigmentation were reported without any long-term side effects. Unlike Ross et al. [9]’s study, which was only effective with black ink, the R0 method permitted multiple passes with different wavelengths within one treatment session. Thus, tattoos with blue, sky blue, white, and red ink were treated effectively.

Our study had a few limitations. First, because the dermatologist’s subjective photographic evaluation forms the basis of our therapy assessment parameters, objectivity may be limited. Secondly, our study had a small sample size and included only Korean patients. Thus, further research with a larger sample size and various ethnicities and skin types should be conducted. In addition, our study did not include follow-up for long-term side effects. Finally, because our study lacked a control group, it is anticipated that a prospective, randomized, controlled trial comparing a group treated with picosecond lasers alone and a group treated with picosecond lasers and PFD will be required in the future. In conclusion, our study demonstrated that the R0 method using picosecond lasers is a time-preserving, effective, and safe modality for tattoo removal in Korean patients.

None.

Conceptualization: SJL. Data curation: SJL. Formal analysis: JL, SJL. Investigation: JL, SJL. Methodology: SJL. Project administration: SJL, HKC. Software: SJL. Validation: SJL. Visualization: JL, SJL. Writing–original draft: JL, SJL, JK. Writing–review & editing: all authors.

Jihee Kim is an editorial board member of the journal, but was not involved in the review process of this manuscript. Otherwise, there is no conflict of interest to declare.

None.

Contact the corresponding author for data availability.

Contact the corresponding author for data availability.