The breast is made up mainly of lobules (milk-producing glands in women), ducts (tiny tubes that carry the milk from the lobules to the nipple), and stroma (fatty tissue and connective tissue surrounding the ducts and lobules, blood vessels, and lymphatic vessels).
Until puberty (usually around 13 or 14), young boys and girls have a small amount of breast tissue consisting of a few ducts located under the nipple and areola (area around the nipple). At puberty, a girl’s ovaries make female hormones, causing breast ducts to grow, lobules to form at the ends of ducts, and the amount of stroma to increase. In boys, hormones made by the testicles keep breast tissue from growing much. Men’s breast tissue has ducts, but only a few if any lobules.