Is multiple wavelength diode laser for facial contouring safe?

The multiple wavelength diode laser (MWDL) is a sophisticated device designed to target deeper skin layers by emitting various wavelengths. Its unique feature is the ability to deliver heat to specific depths within the tissue using different wavelengths while simultaneously cooling the skin surface. Recent research by Choi et al. suggests that wavelengths of 755 and 810 nm can induce carbonization in hair follicles, while the 1064 nm wavelength penetrates deeper into tissues. MWDL has been proposed for fat redistribution in aging, but concerns have been raised regarding ocular safety and potential tissue damage, particularly when used near the eyes. Studies have shown ocular injuries during cosmetic laser procedures, emphasizing the need for robust ocular protection and safety protocols. Additionally, there are reports of internal ischemic necrosis and burns, highlighting the importance of precise energy settings and parameter management. While MWDL shows promise, further research and comprehensive guidelines are needed to ensure safe and effective usage in clinical practice.

The multiple wavelength diode laser (MWDL) stands out as a sophisticated and versatile device meticulously designed to target deeper skin layers through its adept emission of an array of wavelengths.Its unique capability lies in the multifaceted delivery of heat to specific depths within the subcutaneous tissue, achieved by emitting varied wavelengths that penetrate deeper layers.One of the distinctive features of the MWDL is its concurrent provision of skin surface cooling while effectively delivering therapeutic wavelengths.This simultaneous cooling mechanism not only ensures patient comfort during the procedure but also helps in safeguarding the surface layers of the skin from potential thermal impact, thereby enhancing the overall safety and efficacy of the treatment.
As indicated in a recent publication authored by Choi and colleagues, it has been established that wavelengths of 755 and 810 nm possess the capability to induce carbonization within the hair follicle, while the 1064 nm wavelength exhibits a superior ability to penetrate deeper into the tissue.Moreover, the natural aging process leads to the accumulation and redistribution of fat in specific regions of the face.To address this issue, they proposed the use of a multiple wavelength diode laser and advocated for fat redistribution through MWDL (Figure 1).Therefore, they argue that by elevating and relocating volume-increasing areas due to aging, such as the nasolabial fat pad or jowl fat, using energy, fat repositioning could be achieved.
Despite the numerous advantages of this equipment, reported issues of the following nature have been identified. 1,2e crucial issue lies in the absence of a protocol and endpoint for these equipment.Upon examining patients' primary complaints, it has been noted that despite using an eye shield around the eyes when placing the probe nearby, there is still penetration of the laser, particularly with the 1064 laser, due to its simultaneous deep penetration.This poses significant risks and could potentially have a substantial impact on ocular health. 3e review of Huang et al. 3 investigates ocular injuries during cosmetic laser procedures targeting the face, revealing the eye's vulnerability, especially in periocular areas.Over 62% of cases reported inadequate or removed ocular protection during treatment close to the eye, resulting in injuries.Even with intraocular shields and wavelength-specific goggles, accidents occurred in 33% of cases.High fluence, long-wavelength lasers, and insufficient cooling between pulses were identified as exacerbating factors.The findings stress the pivotal role of robust ocular protection and careful laser parameter management to prevent ocular injuries during cosmetic laser treatments, emphasizing the critical need for stringent safety protocols in such procedures.Furthermore, in South Korea, instances of internal ischemic necrosis have been documented, leading to debates about the safety of employing MWDL.(Figure 2).It appears that practitioners are overlooking extravascular bleeding occurring post-injection and proceeding to use lasers, resulting in burns.The author conducted an experiment by injecting a blood-like dye into cadavers and examining them with lasers.The observations made through thermal imaging cameras revealed that the energy did not penetrate deeply but was absorbed by the dye (Figure 3).5][6] Furthermore, it has been observed that when the energy is elevated too high and statically applied, it can result in reaching the periosteal layer, leading to reported pain sensations.Particularly near the zygomatic or mandibular bones where the fat layer is thin, nerve endings in the periosteum might not be adequately protected by surface cooling, thus causing sensations of discomfort or pain.Additionally, there is a report on parotid gland inflammation after the MWDL treatment. 7cording to Choi et al., they discuss that wavelengths of 755 and 810 nm could potentially carbonize the hair follicle, facilitating deeper heat transmission through the follicle.However, this remains a hypothesis that requires experimental validation for precise confirmation.Additionally, since the equipment was initially designed for hair removal purposes, reported incidents of burns around the hair follicles have been documented (Figure 4).Therefore, it is crucial to ascertain the energy levels, settings such as hertz, and other related parameters concerning this energy.
Considering factors such as skin type (Fitzpatrick Scale), determining the most suitable areas where the laser can penetrate deeply through the hair follicles, and assessing the moisture content on the face will ensure the most precise and accurate procedure. 8,9e 1064-nanometer laser possesses minimal scatter, allowing it to penetrate deeply into tissues and generate controlled heating within the subcutaneous layer.Initially, laser therapy was employed to administer energy within the wavelength range of 900-1000 nm, effectively utilized for long-term hair reduction and the treatment of vascular lesions.Nonetheless, challenges arose in effectively and accurately targeting the chromophores within the specific focal fat area (Figure 5). 10,11Research findings have shown that compared to F I G U R E 1 Diode lasers operating at various wavelengths were initially designed for hair removal owing to their efficiency in pinpointing hair follicles.These diverse wavelengths facilitated the entry of a significant portion of energy into the skin through the hair follicles and to some extent through the skin itself.The continuous pulses of the laser over an extended period allowed for substantial penetration into the fatty tissue while concurrently cooling the surface area.
F I G U R E 2 Instances of internal ischemic necrosis have been documented, leading to significant debate and controversy.
the 980 nm wavelength, the 1064 nm wavelength has proven to penetrate tissues at a deeper level. 12ven the lack of comprehensive research in MWDL, the utilization of these devices poses significant risks.Moreover, multi-  In conclusion, while acknowledging the promising advancements that MWDL offers, it is imperative to address the existing gaps in knowledge and regulation to ensure their safe and efficacious implementation in clinical practice.This calls for a collaborative effort involving clinicians, researchers, and regulatory bodies to establish robust protocols and guidelines that safeguard patient safety and optimize the potential benefits of MWDL.

AUTH O R CO NTR I B UTI O N S
All authors have reviewed and approved the article for submission.

CO N FLI C T O F I NTER E S T S TATEM ENT
I acknowledge that I have considered the conflict of interest statement included in the "Author Guidelines."I hereby certify that, to the best of my knowledge, no aspect of my current personal or professional situation might reasonably be expected to significantly affect my views on the subject I am presenting.

DATA AVA I L A B I L I T Y S TAT E M E N T
Data sharing not applicable to this article as no datasets were generated or analysed during the current study.

E TH I C S S TATEM ENT
This study was conducted in compliance with the Declaration of Helsinki.

FI N A N CI A L D I SCLOS U R E
There is no financial disclosure to report.

R E FE R E N C E S
wavelength devices represent innovative laser technology capable of delivering heat energy to deeper layers without pain.However, observed efficacy varies among individuals, particularly when applied to the body, showing decreased effectiveness.This discrepancy might be attributed to various anatomical structures, including water content between fat layers, hair follicles, scattering phenomena, and the reticular dermis.Thus, conducting further research in these areas is imperative.While the use of MWDL has gained substantial traction in the market, particularly in South Korea, it is imperative to underscore the absence of a comprehensive protocol governing these devices.Specifically, a critical observation highlights the inadequate guidance pertaining to crucial facets such as prescribed energy levels, the modality of energy transmission, and clear-cut indications for usage.Primarily, when employing the laser in proximity to ocular areas, despite the eyes being closed, the visibility of red light persists due to its profound penetration capability.This raises concerns about inadvertent exposure and necessitates a deeper understanding of safety parameters, especially concerning delicate areas like the eyes.Secondly, a potential ischemic effect has been identified, potentially leading to the risk of bruising and the accumulation of energy in tissues.This risk underscores the need for a more nuanced comprehension of the implications of MWDL usage, particularly in relation to tissue response and the potential adverse effects associated with prolonged or intensive use.Moreover, uncertainties loom regarding the safety implications when performing laserF I G U R E 3The diode lasers operating at various wavelengths were applied to the thigh area subsequent to dissection (A).Thermal imaging cameras (B) were utilized for observations, indicating that the energy from the lasers was not deeply penetrating but rather being absorbed by the dye.F I G U R E 4Originally, multiple wavelength diode lasers were designed for hair removal, instances of reported burns in the vicinity of the hair follicles have reported.FI G U R E 5 Penetration depth using different laser wavelengths (A) and absorption spectra of different chromophores (B).

| 1591 YI
et al. examinations in regions where fillers have been administered.The possibility of energy concentration in specific areas or any interaction between the laser and filler materials necessitates thorough investigation and elucidation.Furthermore, the impact of MWDL on individuals who have undergone lifting thread procedures remains largely ambiguous.The potential alteration or effect on these threads due to laser interaction necessitates focused research to determine any potential risks or alterations to the outcomes of such procedures.Lastly, until substantial empirical evidence concerning the criteria for treatment endpoints emerges, a cautious and meticulous approach toward the utilization of MWDL is not only recommended but also vital.This highlights the pressing need for rigorous research, comprehensive clinical trials, and the formulation of detailed guidelines to ensure the safe and effective utilization of MWDL in various clinical scenarios.
Kyu-Ho Yi was involved in conceptualization and writing-original draft preparation.Kyu-Ho Yi and Hyun-Jun Park were involved in writing-review & editing.Kyu-Ho Yi, Hyoung-Moon Kim, and Wook Oh were involved in visualization.Hyun-Jun Park and Kyu-Ho Yi were involved in supervision.