At the age of 13, boys will enter puberty, and hormonal changes will occur in the body before puberty, such as hyperplasia and increase in the number of hormones, which will stimulate the breasts and lead to changes in the breasts. If the nodule is directly below the nipple, that is, in the middle of the breast, it may be a normal manifestation whether it is unilateral or bilateral. If the pain, redness and swelling are accompanied by other manifestations, there may be a possibility of infection and you need to go to the hospital for relevant tests, such as hormone levels and ultrasound to see if there are any growths. Under normal circumstances, if a 13-year-old boy has a hard node in the middle of his breast, a slight pain when touched can be normal, and most of them will gradually disappear on their own as their hormone levels stabilize. If it gets bigger or changes gradually and does not disappear gradually as normal, you must find a doctor to do relevant tests to clarify the diagnosis and deal with it in time.