What is normal breast development?

Breast development is a vital part of reproduction in the human female. Unlike other mammals, however, human females are the only ones who develop full breasts long before they are needed to nurse their offspring.

Breast development occurs in distinct stages throughout a woman's life, first before birth, and again at puberty and during the childbearing years. Changes also occur to the breasts during menstruation and when a woman reaches menopause.

The development and kinds of breast changes that take place are directly related to age. There are three phases of development: lobule development, which takes place between the ages of 10 and 25; glandular development, which is under the influence of menstrual hormones and occurs between the ages of about 13 and 45, and involution, or shrinkage of the milk ducts, which begins from about age 35 on.

When does breast development begin?

This first stage of development begins at about six weeks of fetal development with a thickening called the mammary ridge or the milk line. By six months of development this extends all the way down to the groin, but then regresses. At this time, solid columns of cells form from each breast bud, with each column becoming a separate sweat gland. Each of these has its own separate duct leading to the nipple. By the final months of fetal development, these columns have become hollow, and by the time a female infant is born, a nipple and the beginnings of the milk-duct system have formed.

What breast changes happen at puberty?

As a girl approaches adolescence, the first outward signs of breast development begin to appear. When the ovaries start to secrete estrogen, fat in the connective tissue begins to accumulate causing the breasts to enlarge. The duct system also begins to grow. Usually the onset of these breast changes is also accompanied by the appearance of pubic hair and hair under the arms.

Once ovulation and menstruation begin, the maturing of the breasts begins with the formation of secretory glands at the end of the milk ducts. The breasts and duct system continue to grow and mature, with the development of many glands and lobules. The rate at which breasts grow varies greatly and is different for each young woman.