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Breast Development

Breast Development

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Reproductive Endocrine Practice

Breast Clinic

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, 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?

Breasts begin to form during fetal development, with a thickening in the chest area called the mammary ridge or milk line. By the time a female infant is born, a nipple and the beginnings of the milk duct system have formed.

Breast changes continue to occur over the lifespan, with lobes, or small subdivisions of breast tissue, developing first. Mammary glands develop next, and consist of 15-24 lobes. Mammary glands are influenced by hormones activated by puberty. Involution of shrinkage of milk ducts is the final change that occurs within the breast tissue. Involution typically begins around the age of 35.

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 breasts begin to mature and form 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 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.


					Children's Hospital Boston is the primary pediatric teaching hospital of Harvard Medical School

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