A hard lump in the chest in your teens can be caused by breast hyperplasia, breast trauma, and growth and development. 1. Mammary gland hyperplasia: Mammary gland hyperplasia will cause the symptoms of breast enlargement and pain when pressed, mainly due to the rapid increase of estrogen level in the body caused by puberty development, resulting in excessive proliferation of the mammary gland, and the vast majority of them will disappear gradually. 2. Breast trauma: Ask the patient if he/she has a history of trauma. When the mammary glands are extruded by external force or damaged due to trauma, the mammary glands will become red, swollen and painful. Sometimes there may be obvious tenderness, local hematoma will appear after chest trauma, and hard lumps will appear in the chest after mechanization, and breast ultrasound is feasible for differential diagnosis. 3. Growth and development: It may be due to abnormal hormonal disorders in the body, which may also lead to the phenomenon of hard lumps in the chest. Generally speaking, if the hardness in the chest is caused by growth and development, it is not necessary to deal with it, and it will be gradually relieved with the growth of age. Hard lumps in the chest in the late teens may also be caused by breast tumors, chest wall diseases, non-lactating mastitis and other reasons, it is recommended to immediately seek medical attention to identify the cause of the disease, and comply with the doctor’s instructions for treatment, to avoid delays in the condition.