Some young men or men over the age of 50 will find that one or both of their breasts on one side of the chest become enlarged like a woman, and some of them can feel the breast lumps, which is medically known as gynecomastia, or feminization of male breasts. In fact, normal male body can also secrete a small amount of estrogen, male androgen can inhibit breast development. Gynecomastia can be caused when there is a temporary excess of estrogen for some reason, i.e., the androgens in the body are not enough to buffer the intrinsic estrogen or to meet the needs of the vigorous development of the body, and when the breast tissue is sensitive to estrogen. When breast enlargement occurs in adolescent boys (13-15 years of age), it is called idiopathic gynecomastia. This may be related to stimulation of the mammary glands by growth hormone, estrogen and adrenocorticotropic hormone. It is usually not uncomfortable, but can sometimes be accompanied by swelling pressure or tenderness. In addition to the physiological breast enlargement mentioned above, there are also pathologic ones, which are often accompanied by primary diseases. For example, in patients with liver diseases such as cirrhosis, it may be associated with decreased liver function and decreased function of liver cells to process estrogen, resulting in impaired metabolism of androgens in the liver. Other primary diseases, such as adrenal and pituitary diseases can cause an increase in estrogen secretion, resulting in high estrogen levels in the body. Breast enlargement occurs after middle age, which is related to testicular insufficiency, and most of the breasts are proportionate and diffusely enlarged bilaterally, like female breasts, with different sizes, sometimes with nodules; the patients’ voices are shrill and thin, with no whiskers or laryngeal nodes, etc. The patients’ voices are not obvious. Generalized obesity and breast enlargement in adolescent and elderly men without obvious reasons may be due to testicular tumors, liver disease, hyperthyroidism and other systemic diseases, or long-term use of estrogen, spironolactone, metronidazole imipramine and other drugs. This condition is pathological and requires appropriate treatment. Therefore, it must first be differentiated whether it is mammary-type breast hypertrophy due to enlarged mammary tissue, or simple breast hypertrophy due to fat accumulation and obesity only. Clinical examination of the whole body is needed to exclude the above pathologic factors, of which ultrasound examination is of great significance in distinguishing breast tissue hypertrophy from adipose tissue breast hypertrophy.