Alopecia, caused by a psychiatric disorder, hereditary factors, and emotional stress, is extremely common in today’s culture, resulting in terrible physical and psychological consequences [1,2]. In all cases, such hair loss can be classified according to cause and symptoms, and in some cases, it can be classified according to the patient’s sex. In general, hair loss in both male and female can be divided into four types of hair loss disorders: androgenetic alopecia (AGA), alopecia areata, telogen effluvium, and scarring alopecia. This paper focuses on AGA [3].

AGA, commonly called male or female pattern hair loss, is a gradual and non-scarring shrinking of hair follicles that follows a distinctive pattern in predisposed male and female. It is one of the most common reasons for hair-related medical consultations. According to epidemiological studies, around 80% of Caucasian male and 40%-50% of Caucasian female experience AGA at some point in their life, with its prevalence increasing as age advances [4-6]. In Asian populations, the occurrence of AGA is comparatively lower, with 14.1% of Korean male exhibiting signs of AGA [7]. Similarly, a study conducted in the African population reported that the prevalence of AGA was 14.6% in male and 3.5% in female [8]. The etiology of AGA is complex, involving multiple factors and genetic predisposition [9,10]. Hair loss is so prevalent in our society, but effective treatments are lacking. Drugs and currently available treatments such as diet and surgical procedures (Fig. 1) cannot satisfy the satisfaction of most patients due to unsatisfactory and permanent consequences or undesirable adverse effects. Hair follicle transplantation accompanied by surgical treatment is limited due to decreased cell viability and a lack of hair from donors. In addition, results often appear temporarily due to the progressive characteristics of hair loss [1,2,11,12].

Figure 1. Currently available treatments for alopecia.

Low-level laser therapy (LLLT) or photobiomodulation therapy (PBMT) has recently been developed as a monotherapy, adjuvant, and alternative treatment for patients who have failed to respond to conventional medical therapy or are unwilling to undergo surgical procedures. LLLT is effective in various clinical settings, including joint rehabilitation [13], tinnitus treatment [14], anti-inflammatory pain [15,16], neuropathic pain [17], and wound healing [18,19], according to numerous published studies. Also, it has been demonstrated that LLLT improves wound healing and encourages fibroblast migration, collagen deposition, and neovascularization [20,21].

In 1967, during research on the potential carcinogenic effects of laser exposure, Endre Mester observed that mice treated with lasers regrew hair in shaved areas at a significantly faster rate than unexposed mice [22]. Later studies conducted by other researchers found that certain patients demonstrated paradoxical hair growth in areas treated with lasers for hair removal or adjacent to lesions treated with laser sources [23,24].

After these initial observations, several studies, ranging from animal studies to clinical trials, have collectively established the benefits of LLLT for hair loss with minimal side effects, thereby providing new treatment options for this condition [25,26]. LLLT appears to stimulate antigen re-entry of telogen hair follicles and prolong the duration of the antigen phase [27-29]. By regulating the hair cycle, LLLT reduces hair loss and enhances hair density and diameter, leading to a significant clinical improvement in hair loss. However, despite the 10 years of experience with LLLT for hair loss treatment, several options remain challenging, such as selecting the most effective light sources, optimal wavelength, and treatment regimen. Therefore, this study aims to review the clinical research conducted in the past decade on using LLLT for alopecia treatment.

This study aimed to review published studies from the past ten years that affirm the positive effects of LLLT or PBMT on AGA.

The authors searched the PubMed database for papers from the last 10 years using the keywords “lowlevel laser therapy or photobiomodulation or LLLT or PBM, and androgenetic alopecia”. As a result of a keyword-related clinical trial search, a total of 17 papers were published, of which 11 were reviewed. Systematic review and meta-analysis were excluded. The authors selected and prepared papers related to this content, including research topics, titles, and methods.

A total of 11 related papers were obtained from the PubMed database, of which 9 were treatment studies using only LLLT (Table 1) [22,30-37], and the remaining 2 were combined with minoxidil (Table 2) [38,39].

Table 1 . Data of selected laser therapy

Reference	Title	Therapy protocol	Result
Lanzafame et al. (2013) [22]	The growth of human scalp hair mediated by visible red light laser and LED sources in males	Source: TOPHAT655 (helmet-type laser & LED array) Wavelength: 655 nm Period: 60 times for 16 wk, 25 min per times for the global scalp	Low level laser treatment for androgenetic alopecia is safe and effective, with a 35% increase in hair counts
Kim et al. (2013) [30]	Low-level light therapy for androgenetic alopecia: a 24-week, randomized, double-blind, sham device-controlled multicenter trial	Source: helmet-type laser & LED array Wavelength: 630 nm, 660 nm, 650 nm Period: every day for 24 wk, 18 min per times	LLLT group showed significantly higher hair density and improved mean hair diameter
Lanzafame et al. (2014) [31]	The growth of human scalp hair in females using visible red light laser and LED sources	Source: TOPHAT655 (helmet-type laser & LED array) Wavelength: 655 nm Period: 60 times for 16 wk, 25 min per times for the global scalp	Low level laser treatment for androgenetic alopecia is safe and effective, with a 37% increase in hair counts
Friedman and Schnoor (2017) [32]	Novel approach to treating androgenetic alopecia in females with photobiomodulation (low-level laser therapy)	Source: helmet-type LD & LED array Wavelength: 650 nm Period: 30 min per every other day for 17 wk	LLLT achieved a 51% increase (p < 0.001) in hair counts as compared with sham-treated control patients
Mai-Yi Fan et al. (2018) [33]	Efficacy and safety of a low-level light therapy for androgenetic alopecia: a 24-week, randomized, double-blind, self-comparison, sham device-controlled trial	Source: helmet-type LED array Wavelength: 660 nm, 650 nm Period: 3 times per wk for 24 wk, 30 min per times	LLLT-treated scalp had significantly greater hair coverage, hiar thickness, hair count and IGA than sham light-treated side at 12- and 24-week visits
Alhattab et al. (2020) [34]	The effect of 1540-nm fractional erbium-glass laser in the treatment of androgenic alopecia	Source: fractional erbium-glass laser Wavelength: 1,540 nm Period: 10 times at 2-wk intervals Parameter: 7 mm tip, 6 mJ energy, 1 Hz frequency	Hair density and thickness were significantly increased in both males and females
Panchaprateep et al. (2019) [35]	Quantitative proteomic analysis of dermal papilla from male androgenetic alopecia comparing before and after treatment with low-level laser therapy	Source: helmet-type laser & LED array Wavelength: 655 nm Period: 24 wk, 25 min per every day	LLLT increased the dermal papilla and clinically improved hair diameter
Suchonwanit et al. (2019) [36]	Low-level laser therapy for the treatment of androgenetic alopecia in Thai men and women: a 24-week, randomized, double-blind, sham device-controlled trial	Source: helmet-type LD Wavelength: 660 nm Period: 3 times per wk for 24 wk, 20 min per session	The laser helmet outperformed in terms of increasing hair density and diameter, as well as showing a significantly greater improvement in global photographic assessment
Yoon et al. (2020) [37]	Low-level light therapy using a helmet-type device for the treatment of androgenetic alopecia: a 16-week, multicenter, randomized, double-blind, sham device-controlled trial	Source: helmet-type LD & LED array Wavelength: 655 nm Period: 56 times for 16 wk, 25 min per every other day	LLLT had a significant effect on enhancing hair density and thickness for males and females

LED, light emitting diode; LD, laser diode; LLLT, low-level laser therapy; IGA, investigator’s global assessment.

Table 2 . Data of selected combination therapy

Reference	Title	Therapy protocol	Result	Combination therapy
Faghihi et al. (2018) [38]	The effectiveness of adding low-level light therapy to minoxidil 5% solution in the treatment of patients with androgenetic alopecia	Source: laser comb Wavelength: 785 nm Period: 2-3 times per wk for 24 wk, 20 min per session	The LLLT group showed a significantly higher increase in hair count and hair diameter	Each group received 20 drops of topical minoxidil 5% solution twice daily to apply to their balding areas at home for 6 mon
Ferrara et al. (2021) [39]	Efficacy of minoxidil combined with photobiomodulation for the treatment of male androgenetic alopecia. A double-blind half-head controlled trial	Source: helmet-type laser & LED array Wavelength: 655 nm Period: 2 times per day for 6 mon, 12 min per session	No further advantage of LLLT in males with AGA using topical minoxidil was shown	Topical minoxidil application (1 ml of 5% solution) after laser treatment

LED, light emitting diode; LLLT, low-level laser therapy; AGA, androgenetic alopecia.

Helmet-type products were utilized in most clinical studies that solely employed LLLT, with laser diodes, light emitting diodes, and lasers serving as the light sources. The most clinical studies used wavelengths ranging from 630 nm to 660 nm; only one study used 1,540 nm, and treatment times per session varied from 10 to 30 minutes [33-35]. In terms of treatment duration, all 16-week treatments involving helmet types resulted in a greater than 35% increase in hair [22,32], density, and thickness [38] in both males and females. Furthermore, hair density, diameter, and coverage [31,34,37], and the effect of increasing hair dermal papilla [36], were confirmed for all 24-week treatments that utilized a helmet type. Moreover, tests conducted after 2 and 17 weeks demonstrated a significant increase in hair number, density, and thickness [33,35].

In addition to LLLT-only treatments, two tests were conducted with a combination of minoxidil and LLLT, and the results varied. Both tests were prescribed for a period of 6 months with a 5% concentration of minoxidil, but the number of LLLT treatments and wavelengths used differed. Tests that received treatment two to three times per week showed a significant increase in hair number and diameter [39], while no significant difference was observed in tests that received treatment twice per day [40].

Oral finasteride and topical minoxidil are currently available treatments for AGA with the highest evidence level. The options for treating AGA are still limited, despite the availability of oral and topical antihormonal medications as well as surgical procedures [40]. LLLT treatment, which is non-invasive and has local effects despite these limitations, can be a new alternative.

Non-invasive and safe, LLLT has demonstrated a significantly lower incidence of adverse events when used for more than 50 years in various medical states and anatomical sites. In addition, it was reported to be convenient for patients to use at home and stimulate hair growth in male and female with AGA, and was approved by the U.S. Food and Drug Administration in 2007 [41-42].

A total of 11 studies were reviewed in this study after reviewing papers published over the past 10 years to verify the effect of LLLT or PBMT on recovery from alopecia. Near-infrared wavelengths were used for LLLT or PBMT, and it was confirmed that they had effects such as increased hair number, density, thickness, and coverage. It has also been confirmed that it works regardless of sex. When using a long-wavelength laser, it was confirmed that there was a significant effect even though the treatment period was short—2 weeks, unlike other studies.

Platelet-rich plasma injection, micro-needling, and stem cell therapy have recently been proposed as new treatments, but there is currently a lack of evidence-based information on related protocols, and more research is needed to become standardized [43-45].

In summary, research is underway to use near-infrared wavelength bands and apply various parameters, and LLLT has confirmed that it has the effect of increasing hair number, density, and patient satisfaction with AGA, and has the potential for treating alopecia through complex treatments combined with various treatments. Furthermore, AGA is used in the majority of current LLLT alopecia studies. There is a need for continuous research on the efficacy of LLLT or PBMT for various alopecia.

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Conceptualization: HSR, PSC, SHW. Data curation: HSR. Funding acquisition: PSC. Investigation: HSR. Validation: CA. Visualization: AP. Writing–original draft: HSR. Writing–review & editing: all authors.

Seung Hoon Woo is the Editor-in-Chief of the journal but was not involved in the review process of this manuscript. Celine Abueva, Andrew Padalhin, and Phil-Sang Chung are editorial board members of the journal but was not involved in the review process of this manuscript. Otherwise, there is no conflict of interest to declare.

This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF), funded by the Ministry of Education (NRF-2020R1I1A3072797 and NRF-2020R1A6A1A 03043283), Leading Foreign Research Institute Recruitment Program through NRF funded by the Ministry of Science and ICT (NRF-2023K1A4A3A02057280), Korea Health Technology R&D Project through the Korea Health Industry Development Institute (KHIDI) funded by the Ministry of Health & Welfare (HI20C2088), Korea Medical Device Development Fund grant funded by the Ministry of Science and ICT, the Ministry of Trade, Industry and Energy, the Ministry of Health & Welfare, the Ministry of Food and Drug Safety (KMDF_PR_20200901_0027-03), Republic of Korea.

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