Normal Breast Development

Each breast has 15 to 20 sections, called lobes, that are arranged like the petals of a daisy. Each lobe has many smaller lobules, which end in dozens of tiny bulbs that can produce milk.

The lobes, lobules, and bulbs are all linked by thin tubes called ducts. These ducts lead to the nipple in the center of a dark area of skin called the areola. Fat fills the spaces between lobules and ducts.

Anatomy of breast.Breast development is a normal part of development in the human female. 

Breast development occurs in distinct stages, first before birth, again at puberty and is complete during the childbearing years. Changes 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 10 and 45, and involution, or shrinkage of the milk ducts, which begins from about age 35 on.

As a girl approaches adolescence, the first outward signs of breast development begin to appear. When the ovaries start to secrete estrogen, this causes the breasts to enlarge. The duct system also begins to grow. Usually, the onset of these breast changes is 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.

What cyclical changes occur to the breasts during menstruation?

Each month, women experience fluctuations in hormones that make up the normal menstrual cycle. Estrogen, which is produced by the ovaries in the first half of the menstrual cycle, stimulates the growth of milk ducts in the breasts. The increasing level of estrogen leads to ovulation (releasing of the egg) halfway through the cycle, and then the hormone progesterone takes over in the second half of the cycle, stimulating the formation of the milk glands. These hormones are believed to be responsible for the cyclical changes such as the swelling, pain, and tenderness that many women experience in their breasts just before menstruation.

During menstruation, many women also experience changes in breast texture, with breasts feeling particularly lumpy. These are the glands in the breast enlarging to prepare for a possible pregnancy. If pregnancy does not occur, the breasts return to normal size. Once menstruation begins, the cycle begins again.

Your healthcare provider is an excellent resource for questions about breast development. Always bring concerns to their attention to rule out normal versus abnormal developmental concerns. 

Last Updated 03/2016