Gynecomastia can be seen in men of all ages, including adolescent men and middle-aged and older men. Unilateral breast enlargement is usually common, but sometimes it can be bilateral. Men have the same breast tissue as women, and when the breast tissue is enlarged, the breast will increase in size. There are two types of gynecomastia: physiological and pathological. The former usually heals on its own, while the latter usually requires surgery to resolve. Physiologic and pathologic gynecomastia have different manifestations. 1. Physiological gynecomastia 1. Large breasts in newborns, which disappear about a week after birth, and rarely last for several years, is due to the influence of estrogen produced in the blood circulation and the placenta. 2. Young developing boys, either early or late, have varying degrees of breast development, accounting for about 70% of boys. This may be due to the increased sensitivity of the breast tissue during this period. It lasts for several years and gradually disappears on its own, or may not subside for life, called idiopathic breast development. 3, after middle age, when men begin to decline in sexual function, often have breast development phenomenon, may be due to increased secretion of pituitary gonadotropin, causing an imbalance in the balance of sex hormones. Second, pathological gynecomastia 1, testicular tumors. Such as chorionic epithelial carcinoma, mesenchymal cell tumor. 2.Adrenocortical tumors with feminization. They are often malignant and occur in adolescence or adults. In addition to breast development, they are accompanied by testicular atrophy, penile shrinkage and hypogonadism. Increased urinary ketosteroid and estrogen excretion. 3. Hypothyroidism. It may be accompanied by increased thyroid stimulating hormone, gonadotropin and other pituitary hormones. 4, abnormal gonadal development. Such as male pseudohermaphroditism, testicular dysplasia, accompanied by increased pituitary gonadotropins. 5. Impaired liver function such as cirrhosis, hepatocellular carcinoma and hepatitis. It may be due to the weakened inactivation of estrogen in the body, which increases estrogen levels.