Sudden enlargement of male chest may be caused by physiological factors such as fitness and obesity, or it may be related to pathological factors such as decreased secretion of androgens, excessive secretion of estrogens, breast cancer, Crohn’s syndrome and so on. 1. Physiological factors: such as fitness people often chest exercise, chest muscles are relatively developed, the symptoms of chest enlargement can occur. Besides, obese men can also show symptoms of sudden enlargement of chest due to increased accumulation of chest fat. 2. Pathological factors: (1) Decrease in androgen secretion: such as mixed gonadal hypoplasia, insufficient androgen resistance synthesis, viral orchitis and other causes of testicular hypoplasia, decrease in androgen secretion, imbalance in the ratio of male hormones, which can cause the symptoms of sudden enlargement of chest. (2) Excessive secretion of estrogen: such as taking hormone drugs, hepatic hypogonadism, adrenocortical tumors, etc. can cause excessive secretion of estrogen and hormone imbalance in men, which will lead to symptoms such as sudden enlargement of chest, testicular atrophy, hypogonadism, and reduction of semen. (3) Breast Cancer: Breast cancer in men can cause localized lumps in the breast leading to chest enlargement, which may be accompanied by symptoms such as nipple overflow, cellulite-like skin changes and enlarged lymph nodes in the armpits, etc. However, this kind of disease is relatively more common in men. However, this kind of disease is relatively rare in men. (4) Crohn’s syndrome: mainly related to chromosomal disorders, it can cause sexual dysfunction, spermlessness, small testicles and other symptoms in men, and can also be accompanied by enlarged breasts. At the same time, gynecomastia may be associated with taking certain medications (resulting in a decrease in estrogen degradation) that can contribute to breast development. Excluding physiological factors, men whose breasts suddenly become larger are advised to go to the hospital in time to find out the cause of the enlargement of the chest, and actively carry out targeted treatment to avoid delaying the condition.