## 4 Clinical Indications
### Pigmentation Disorders  
The picosecond laser is an advanced technology which proved to be beneficial in treating benign pigmentation disorders, including freckles, solar lentigines, melasma, Hori's nevus, Ota's nevus, and post-inflammatory hyperpigmentation [38]. These skin lesions constitute a common aesthetic concern and can negatively impact the well-being and self-esteem of the affected individuals [39]. The treatment of pigmentation disorders poses a challenge, especially in individuals with higher skin types (III-IV) as compared to those with lighter skin tones [40]. Apart from genetically determined skin phototype, the depth of the pigmentary lesions plays a crucial role as far as the success of laser therapy is concerned. Dermal pigmentation disorders, in contrast to epidermal lesions, are more resistant to medical interventions, tend to be chronic in nature, are associated with a higher risk of PIH, and usually require a higher number of treatment sessions [41]. Extensive photothermal damage, which may be induced by lasers, is a common cause of complications in patients with darker skin types. That fact contributed to the development of PS laser technology, which relies on photoacoustic destruction rather than photothermolysis [6]. PS lasers, emitting wavelengths of 532 nm, 755 nm, and 1064 nm, which effectively fragment pigment clusters into smaller particles with minimal thermal effects, thus reducing the risk of inflammation and PIH, are used [42; 43]. Melasma, which manifests as irregular, light-to-dark brown patches on the face, is one of the most prevalent and recurrent pigmentation disorders in women [44]. The Nd:YAG (1064 nm) PS laser is often used for treating melasma. [PERSON] et al. [45], conducted a study using this laser, equipped with a fractional handpiece with microlens array, among 20 adult individuals of both sexes (Fitzpatrick I-IV) with facial melasma. The participants underwent a series of four monthly treatments. Skin reaction was assessed immediately after the session, and therapy efficacy was evaluated by dermatologists through photographic analysis at 3 and 8 months after treatment completion using the Modified Melasma Area and Severity Index (mMASI). Also, the patients rated their discomfort and satisfaction level after each session. Significant improvement of the skin condition and less visible melasma was found at 3 and 8 months post-treatment, which was consistent with the patient-reported outcomes. All treatments were well-tolerated by the patients, with only  
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mild and transient side effects (erythema and edema), and low pain scores (mean: 3.8 \(\pm\) 2.3 on an 11-point scale) [45]. [PERSON] et al. [46] also used a fractional Nd:YAG (1064 nm) PS laser in Asian women with Fitzpatrick skin types III-IV and facial melasma. The participants underwent nine treatment sessions every 4-6 weeks. The efficacy of the therapy was assessed using the mMASI score, based on photographs taken at 6 and 12 weeks post-treatment. The total mMASI score decreased by 75% at 6 weeks and by 66.7% at 12 weeks after therapy completion. Furthermore, 75% of the women reported visible skin improvement as compared to baseline within 6 weeks of treatment, which was consistent with high levels of satisfaction with the outcome. The main objective of that study was not only to evaluate the efficacy of fractional Nd:YAG PS laser therapy for melasma, but also to assess its safety for darker skin types. Mild erythema (84.4%) and edema (1.1%), both of which resolved within one week, were the most common adverse events. No cases of hypo- or hyperpigmentation were observed, and the procedure was described as'minimally painful' by the participants. These findings suggest that the fractional Nd:YAG PS laser is an effective, well-tolerated, and, most importantly, safe treatment option for treating melasma in Asian skin types [46].