The breasts are mainly composed of breast glands, fat and connective tissue, and there are several reasons why female breasts increase significantly: 1. Women, due to the increased secretion of estrogen and progesterone, will also lead to breast enlargement. 4, breast diseases, such as breast cancer, inflammatory breast cancer, benign breast disease lumps suddenly become larger, will lead to a corresponding increase in breast size. In men, breast enlargement can also occur in adolescent men and older men due to excessive secretion of estrogen or insufficient secretion of androgens, and male breast cancer can also lead to relatively larger breasts.