Melasma is a common and refractory pigmentary skin disorder manifested as light to dark brown patches on the facial skin. It belongs to disfiguring dermatoses and significantly affects the physical and mental well-being of patients. Conventional treatments for melasma, including pharmacological and photoelectric therapies, have high recurrence rates and suboptimal clinical efficacy. Preliminary evaluations of the therapeutic effects of human umbilical cord mesenchymal stem cells (MSCs) in melasma mouse models have shown that MSCs can significantly improve skin pigmentation, reduce malondialdehyde (MDA) levels indicating anti-aging effects, ameliorate skin inflammatory cell infiltration, and promote skin repair in these models. This study is a single-center, randomized controlled clinical trial aiming to build on previous experimental findings by combining MSCs with photoelectric therapy for the treatment of melasma. Patients will be divided into three groups of 10 each: Stem Cell Treatment Group 1, Stem Cell Treatment Group 2, and a Control Group. Group 1 will receive intravenous infusion of MSCs followed by multi-point injection into the melasma area in combination with 755nm picosecond laser treatment. Group 2 will receive multi-point injection of MSCs into the melasma area in combination with 755nm picosecond laser treatment. The Control Group will only receive 755nm picosecond laser treatment. Efficacy will be initially assessed based on parameters such as the Melasma Area and Severity Index (MASI), VISIA skin analysis, and patient satisfaction. The study aims to evaluate the efficacy and safety of MSCs combined with photoelectric therapy for melasma and to investigate the underlying mechanisms.

Inclusion Criteria:

1. Subjects must voluntarily participate in this study and sign a written informed consent form.
2. Subjects are female patients with melasma aged between 18 and 60 years. Their diagnosis should conform to the "Chinese Expert Consensus on Diagnosis and Treatment of Melasma (2021 Edition)" formulated by the Pigmentary Disorders Subgroup of the Dermatovenereology Committee of the China Association of Integrative Medicine. The skin lesions manifest as light brown or dark brown patches of varying depths and with indistinct borders on the cheeks, forehead, and jaw. Subjects must be excluded from having post-inflammatory hyperpigmentation, naevus of Ota, Riehl's melanosis, pigmented lichen planus, and other skin diseases. Additionally, their melasma should have been in a stable phase for 3 months or more.
3. Subjects have never undergone stem cell therapy or laser treatment for melasma.

Exclusion Criteria:

1. Subjects with a history of photosensitivity or allergies to biological medications.
2. Subjects who are pregnant or lactating.
3. Subjects who have a history of alcohol abuse, drug addiction, or substance abuse in the past 24 months.
4. Subjects with concurrent severe systemic diseases, malignancies, or psychiatric disorders.
5. Subjects with active infections, including bacterial, fungal, and viral infections.
6. Subjects with keloid constitution.
7. Subjects with a history of severe sun exposure within 4 weeks before enrollment.
8. Subjects deemed unsuitable for enrollment by the investigator for various reasons or any other conditions that the investigator believes may compromise the safety or compliance of the subject or hinder the successful completion of the study.