Jump to navigation. Breast development is caused by hormones released by the ovaries at puberty. These hormones cause fat to accumulate, causing your breasts to enlarge. The first sign of breast development is slight swelling under the nipple, a stage of development called breast buds. As your breasts first start to grow, they can be very tender and sore.
Boobs are a subject of mystery and concern at puberty, both for boys and girls. What are they like? How big should they be?
There is no perfect shape or size for breasts. Normal breasts can be large or small, smooth or lumpy, and light or dark. Your breasts start growing when you begin puberty. During puberty the hormone levels in your body change, which causes your breasts to develop and your periods to start.