If a hard lump appears in the breast at the age of 16, it is generally considered to be caused by the normal breast nucleus, which is often caused by hormonal disorders, especially in women with irregular menstruation, mainly due to hormonal levels, such as excessive secretion of estrogen and progesterone, and thus induced by it. You should go to a breast specialist as soon as possible to improve the relevant examination, such as ultrasound. If malignancy is suspected, pathology should be done to control it according to the results. If it is a physiological nucleus, it is not serious and it is not a big problem. If it is a breast tumor, it is more troublesome and requires surgical intervention.