Melasma, also known as “liver spot” and “butterfly spot”, is a common skin disease that occurs on the face with excessive pigmentation. Melasma is common in young and middle-aged women, especially during pregnancy, postpartum and women taking oral contraceptive pills, and the condition is seasonal, heavy in summer and light in winter. It is a light brown or yellowish brown spot with clear but irregularly shaped lesions, symmetrically distributed near the eyes, forehead, eyebrow arch, nose, cheeks, lips and perioral area, etc. It has no conscious symptoms and is chronic and aggravated by sunlight. Due to the impact on aesthetics, chloasma will bring serious psychological burden to patients, and serious cases may affect work and life. The causes and pathogenesis of melasma are complex and have not yet been fully elucidated. The following is a brief description of the common causes and pathogenesis: Melasma and endocrine: 1, sex hormone abnormalities: sex hormone abnormalities are recognized as the primary cause of melasma, among which estrogen and progesterone are the main factors affecting the disease. Estrogen can increase the production of melanin by lifting the inhibitory effect of glutathione or sulfhydryl group on tyrosine. 2, thyroid hormone abnormalities: thyroxine in thyroid hormone can promote the oxidation process of tyrosine and melanin, and reduce the sulfhydryl group in epidermis and increase the formation of melanin. Melasma and sunlight irradiation, thermal stimulation: UV light or thermal stimulation in sunlight can make the oxidation of sulfhydryl groups in the skin and activate and increase the tyrosinase activity of the skin, which in turn activates melanocytes and makes them divide faster and increase their activity, and increases the number of melanocytes per unit area, the secretion of melanin vesicles is strong, and the movement of diffusion is accelerated, causing skin pigmentation. In summer, ultraviolet radiation is strong, but in winter, it becomes weaker, so melasma patients mostly show the change of heavy summer and light winter. Melasma and oxygen free radical damage: The formation and removal of oxygen free radicals in human body are always in a dynamic balance, while free radicals are continuously generated and removed. In melasma patients, the oxidation and antioxidant balance in the body is mostly disrupted. The excessive generation of oxygen free radicals and the decrease of antioxidant enzyme activity in the body can cause lipid peroxidation of biological membranes, so that the structural function of membranes is damaged and melasma is caused. Melasma and blood rheological changes: Modern medicine found that patients with melasma have abnormal blood rheological indexes, and it is believed that qi stagnation and blood stasis are related to increased blood viscosity. Other factors: Genetic factors, microbial imbalance in the lesion area, mental factors, and the influence of certain gynecological diseases may all contribute to the development of melasma.