When the level of estrogen in male body rises or the ratio of estrogen and androgen is imbalanced, the breast tissue will develop and proliferate under the stimulation of estrogen, i.e. gynecomastia. Men in puberty can occur a transient breast enlargement, androgen levels decline in the body of older men, breast hyperplasia will occur, both of which are normal physiological phenomena; if it occurs in other age groups, it is a pathological phenomenon. Diseases or medications that cause an increase in estrogen in the body can lead to male breast enlargement, such as liver dysfunction, testicular tumors, adrenal tumors, chromosomal abnormalities, and long-term use of medications such as estrogen, isoniazid, cimetidine, spironolactone, and so on. Male breast hyperplasia can be felt as firm breast tissue under the areola, and ultrasound can detect thickened and enlarged breast glands. Breast glands also look more prominent in obese men, but ultrasound is only fatty tissue, which can be differentiated from male breast hyperplasia. Patients with male breast enlargement need to find the cause of the condition and treat the disease that is causing the hormonal abnormalities in the body. If the breast enlargement is more serious and affects aesthetics, it can be treated surgically. In addition, men can have breast cancer, only very rarely. If a man finds a localized lump in his breast, he needs to be alerted to the possibility of breast cancer and treated as soon as possible.