Gynecomastia is a condition in which the stroma and ducts of the male breast are more numerous than normal and the breast shape is larger than normal. The breast tissue under the areola can be palpated on examination and the diameter is >2 cm or more. About 90% of male breast masses are gynecomastia. However, gynecomastia must be differentiated from the surrounding localized fat. Gynecomastia is still relatively common and can be seen in certain physiologic states or pathologic states. Self-examination is mainly to feel the mammary glands and see if there are any of the above characteristics. If so, go to the endocrinology department as soon as possible to complete the relevant examination to determine the cause of breast development. After determining the cause of the disease, you can formulate a more targeted treatment program.