## 4 Clinical Indications
### Pigmentation Disorders
The literature offers a report about a combination laser therapy using a 1064 nm PS laser and a 1927 nm thulium laser for melasma reduction in a 44-year-old female [47]. During the procedure, both lasers were used simultaneously, first the pigmented lesions were treated with a non-ablative PS laser (1064 nm), and next, the thulium laser, which generates a dense network of microthermal injury zones, followed by pigment migration from the deeper dermis and epidermis, while stimulating controlled healing and dermal remodeling. Erythema, persisting for 3 days, developed immediately after the procedure. The patient also reported transient darkening of the lesions for about 7 days, followed by gradual fading over the course of the next 3-4 weeks. At 4 weeks of follow-up, a noticeable lightening of the pigmentation lesions was observed, indicating the effectiveness of the combined laser approach [47]. Promising results of treating melasma with 755 nm PS lasers have also been reported. [PERSON] et al. [48], compared the efficacy and safety of using the 755 nm PS laser in melasma treatment by applying a fractionated beam (diffractive lens array) on one side and a full beam (flat optics) on the other side of the face. The study included 18 women with Fitzpatrick skin types IV and V and mixed-type melasma. All participants underwent five treatment sessions at monthly intervals. Treatment efficacy was assessed through comparative analysis of the photographs taken at baseline and after therapy completion, as well as at 1, 3, and 6 months post-treatment, and by measuring melanin concentration and size of the melasma-affected area. The physicians observed a 25% reduction in melasma severity with both lasers, which correlated with the improvement reported by the patients. The measurements of melanin concentration and area with melasma revealed a tendency toward improvement on both sides of the face. No statistically significant differences between the results of applying the two laser modalities were observed during the follow-up visits. Objective assessments of melasma severity aligned with the clinical evaluation. However, the full beam (flat optics) treatment was associated with a lower PIH incidence as compared to the fractionated beam [48]. [PERSON] et al. [49] compared the efficacy and safety of three melasma treatment modalities: a non-fractional PS Nd:YAG laser (1064 nm), a non-fractional PS alexandrite laser (755 nm), and a 2% hydroquinone cream among 60 patients with Fitzpatrick skin types III-IV. The participants were randomized into three groups. The laser groups underwent three treatment sessions at 4-week intervals, while the third group applied hydroquinone cream twice daily for 12 weeks. All groups demonstrated a significant decrease in MASI scores from week 4 to week 24 as compared to baseline. The lowest MASI values were observed in the Nd:YAG laser group, while the MASI scores in the alexandrite laser (755 nm) group and the hydroquinone cream group were comparable. At the same time, patient satisfaction scores were highest in the Nd:YAG laser group, followed by the alexandrite laser group, with the hydroquinone group reporting the lowest satisfaction levels. Melasma recurrence was reported in only four patients (6.8%). Other adverse events were transient, resolving within 1 week to 6 months. These findings suggest that the non-fractional PS Nd:YAG laser is more effective in the reduction of melasma than the non-fractional PS alexandrite laser, whose efficacy was comparable to that of 2% hydroquinone cream therapy [49]. Apart from melasma, other common hyperpigmentation disorders include freckles, lentigines, and post-inflammatory hyperpigmentation. [PERSON] et al. [50] investigated the long-term efficacy of the 755 nm PS alexandrite laser in reducing PIH. They analyzed two cases of post-traumatic PIH in individuals with Fitzpatrick skin type III, treated with a combination of the 755 nm PS alexandrite laser and either a diffractive lens array or a zoom handpiece.