Adolescent boys have hard lumps with pain in their breasts, mostly due to the effect of estrogen, the causes of which are mainly caused by male mammary gland development and hyperplasia, chest folliculitis, chest lipoma, male mammary fibroids, and localized hyperplasia. 1. Male mammary gland development and hyperplasia: puberty easily leads to estrogen abnormality in male body, which causes mammary gland hyperplasia, part of male accompanied by chest pressure pain and other phenomena, which is mostly physiological phenomenon. 2. Chest folliculitis: if male skin oil secretion is exuberant or endocrine disorders, it will lead to clogging of the pores of chest skin, forming folliculitis, resulting in hard lumps and pain in the chest. 3. Chest lipoma: abnormal accumulation of fat in the chest can cause benign tumors, usually related to high-calorie diet, which will lead to hard and painful breast lumps. 4. Male Breast Fibroma: Male breast will develop breast fibroma in case of abnormal estrogen secretion or sensitivity to estrogen, and a few patients will experience pain. 5. Localized hyperplasia: If scar tissue occurs in the healing of trauma, excessive hyperplasia and other conditions will occur, resulting in hard lumps of slight itching and pain in the male breast. Adolescent boys with hard lumps in the breast accompanied by pain, it is recommended to go to the hospital in a timely manner to carry out relevant examinations to find the cause, for the cause of the conditioning and treatment.