Androgenetic Alopecia (AGA) is one of the most common causes of hair loss, mediated by androgenic hormones and inflammatory factors. In this pathology, terminal hairs gradually transform into vellus hairs, leading to hair miniaturization and subsequent baldness [1, 2]. Among the treatments for this condition, Minoxidil® and Finasteride are the most commonly used drugs; however, side effects from these medications have been reported by users [3]. Phototherapy, using low-power lasers or LEDs, has been identified as an effective, non-inva- sive treatment for AGA with no side effects, approved by the FDA (Food and Drug Admin- istration) [4]. Red light, with wavelengths ranging from 625 nm to 740 nm, is the wavelength of choice for researchers and works by absorption by Cytochrome C Oxidase, promoting ATP synthesis by the Mitochondria, modulating Reactive Oxygen Species and Nitric Oxide with consequent influence on the Wnt/γ-catenin pathway [5].

Blue light, with wavelengths ranging from 415 nm to 495 nm, has been pointed out as a potential treatment for AGA by researchers who identified photoreceptors in the hair follicle such as OPNS2 and OPSN3 [6] and Cryptochrome 1 [7], enabling the absorption of this wave- length to promote reactions of mesenchymal cells in the dermal papilla, as well as anti.

A prospective, randomized, blind clinical trial was conducted in Campinas, SP, with the approval of the Ethics Committee of Universidade Brasil, under opinion number 5.761.579. An initial anamnesis and clinical evaluation were conducted according to inclusion and ex- clusion criteria, and the selected participants (n=10) were randomly divided into two groups according to the therapeutic intervention: Red Light Group (GLV, n=5) and Blue Light Group (GLA, n=5) (Figure 1). The randomization was performed using a Mobile App Randomizer (GIANNIS MACHERAS). All volunteers were treated using the Vênus equipment (MMOptics, São Carlos, Brazil) applied to the affected area. Both groups received the same light energy density (4J) per point (Table 1).

The interventions were conducted once a week for 90 days, totaling 12 treatment ses- sions. Previously, the volunteers' hair was cleansed with a 0.5% chlorhexidine solution. The applications were made to the upper zone of the head, in areas affected by alopecia, in a

pinpoint manner, at every 1 cm distance, totaling 16 points. All participants and the equip- ment operators wore protective glasses. The emergence of new hairs and the counting of vellus and terminal hairs were conducted using digital trichoscopy imaging (Dino Lite; New Taipei City, Taiwan, China). The Shapiro-Wilk test for normality was used for the statistical evaluation of the treated groups, and the paired T-test was used for comparing the means.

Figure 1: Illustrative image of the interventions. A. Application points.

Table 1: Parameters of irradiation applied. A. Group GLV (Red Light Group). B. Group GLA (Blue Light Group).

The evolution of the hair and the emergence of new strands were observed by comparing the photographic records and digital trichoscopy images, as shown in Figures 2 and 3.

In both treatments, with both red and blue light, it was possible to observe improvements in hair density. All volunteers reported an improvement in the perception of the volume of their hair and none of the volunteers reported discomfort or adverse effects.

In Figure 2, it is possible to observe the evolution of the hair before and after the AGA treatment, through red light. After the 12 treatment sessions, it was possible to notice a reduction in the central hair parting, in all participants treated with red light, in the parameters tested in this study.

Figure 2: Photographic and trichoscopy images, beforeand after interventions with red light.

In Figure 3; it is possible to observe the evolution of the hair before and after the AGA treatment, through blue light. After the 12 treatment sessions, it was possible to notice a reduction in the central hairline, in all participants treated with blue light, in the parameters tested in this study.

Figure 3: Photographic and trichoscopy images, before and after interventions with blue light.

Hair count by trichoscopy, before and after irradiation with red light (Figure 4 A), showed a statistically significant difference in the  Hair count by trichoscopy, before and after irradiation with red light (Figure 4 A), showed a statistically significant difference in the number of terminal hairs (p = 0.0384). While the number of vellus hairs did not show a statistically different difference, after treatment with red light (p = 0.1139). As well as hair count by trichoscopy, before and after irradiation with blue light (Figure 4 B) showed a statistically significant difference in the evaluations of the number of coarse hairs (p = 0.0062). While the number of vellus hairs did not show a statistically different difference, after treatment with red light (p = 0.1586).

Figure 4: Graphical representation of the total number of terminal hairs and vellus hairs, before and after treatment with red (A) and blue light (B).

Regarding the number of thick terminal hairs before any treatment, Figure 5 A shows that there was no statistically significant difference between the two treated groups (p = 0.269). Likewise, the different wavelengths used in the treatment of AGA did not show any statistically significant difference after the treatments (p = 0.333) (Figure 5 B).

Figure 5: Graphical representation of the total number of terminal hairs, before (A) and after (B) treatment in the comparison of red light with blue light.

Regarding the number of fine terminal hairs/vellus before any treatment, Figure 6 A shows that there was no statistically significant difference between the two treated groups (p = 0.579). Likewise, the different wavelengths used in the treatment of AGA did not show any statistically significant difference after the treatments (p = 0.190) (Figure 6 B).

Figure 6: Graphical representation of the total number of vellus hairs, before (A) and after (B) treatment in the comparison of red light with blue light.

We dedicate this study to seeking options that can promote hair improvement in indi- viduals affected by Androgenetic Alopecia, as it is one of the conditions that most commonly causes hair loss, affecting both men and women and causing psychosocial discomfort and consequently impacting the quality of life of affected individuals. Red light emerges as a fa- vorite for phototherapy treatment; however, new research points to the possibility of treat- ment with blue light with mechanisms like those of photobiomodulation. Through this study, it was possible to observe that both red and blue wavelengths, under the parameters tested here, promoted improvements in the volunteers' hair, with increased density and reduced central parting. Additionally, in this study, we evaluated the thickness of the hair affected by the pathology and observed that phototherapy altered the ratio between terminal and vellus hairs in both groups, thus allowing for the reduction of the central parting of the hair.

We also observed that the volunteers in the group treated with blue light, in addition to improvements in density, also experienced a decrease in scalp erythema and seborrhea, as well as an increase in hair color, findings consistent with those reported by Buscone et al. [6]. Given the benefits found in the results of this study regarding the use of red and blue light in the treatment of Androgenetic Alopecia, further studies are encouraged to evaluate the com- bined use of the two wavelengths. This approach could potentially increase the number of light receptors, thereby triggering simultaneously different mechanisms of action of photo- therapy.

According to the results presented by comparing treatments with different wavelengths of light, it was found that phototherapy is effective, safe, and can be an option in the treatment of Androgenetic Alopecia (AGA). Both red and blue light, under the parameters tested in this study, allowed for increased hair density, reduced central parting, and promoted an increase in the number of terminal hairs after treatments, as well as a reduction in vellus hairs.

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