Gynecomastia (GYN) is a clinical condition in which male breast tissue develops abnormally and the connective tissue of the breast grows abnormally due to an imbalance in the ratio of estrogen to androgen caused by physiological or pathological factors. GYN is physiologic in 50% of cases, most commonly in neonatal and adolescent years, when it is transient and usually benign, but is considered abnormal if it occurs in prepubertal, adolescent, and middle age and requires further testing to rule out the possibility of breast cancer or other neoplastic organisms. Epidemiology: GYN can occur at any age, with most occurring between the ages of 12 and 17. In recent years, as people’s standard of living has improved and their lifestyle has changed, the incidence and consultation rates for this disease have increased significantly. The reported incidence varies from 30% to 70%, and the incidence varies by age. Rohrich reported the incidence of GYN in male population as 32%-65%, Chen Zhangqing et al. reported the incidence of GYN in neonates as 50% or more, in adolescents as 39%, and in the elderly as 40% or more. Pathogenesis: It is believed that GYN is mainly caused by the disturbance of sex hormone levels in blood circulation, and there are basically two kinds of disturbance of sex hormone levels: one is the increase of estrogen, and the other is the increase of estrogen/androgen ratio. On the one hand, elevated estrogen can promote male breast growth and development, on the other hand, increased estrogen/androgen ratio can also stimulate the synthesis of sex hormone binding protein (SHBG), which has a much greater affinity for androgens than estrogen, thus increasing the ratio of biologically active free estrogen/androgen in the blood and promoting breast enlargement. In addition, it is thought that the occurrence of GYN is also related to the local estrogen/androgen ratio in the breast and the response of the breast to hormones. In some cases, the local aromatase activity in the breast increases, resulting in the conversion of more androgens to estrogens, resulting in a local excess of estrogen and causing GYN. The effect of androgens is reduced, while the effect of estrogen is relatively enhanced, resulting in mammary gland hyperplasia. For example, Xu Peiheng et al. reported that there was no significant difference in serum I and water K levels in GYN patients compared with the control group, while the AR binding capacity was significantly lower than that of the control group, suggesting that GYN is caused by a decrease in AR, which prevents the biological effects of testosterone from functioning normally.