Normal Breast Development

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 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.

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.

What happens to the breasts during pregnancy and lactation?

Many physicians believe the breasts are not fully mature until a woman has given birth and produced milk. Breast changes are one of the earliest signs of pregnancy - a result of the pregnancy hormone, progesterone. In addition, the areolas (the dark areas of skin that surround the nipples of the breasts) begin to swell followed by the rapid swelling of the breasts themselves. Most pregnant women experience tenderness down the sides of the breasts and tingling or soreness of the nipples because of the growth of the milk duct system and the formation of the many more lobules.

By the fifth or sixth month of pregnancy, the breasts are fully capable of producing milk. As in puberty, estrogen controls the growth of the ducts and progesterone controls the growth of the glandular buds. Many other hormones, such as follicle stimulating hormone (FSH), luteinizing hormone (LH), prolactin, oxytocin, and human placental lactogen (HPL) also play vital roles in milk production.

Other physical changes, such as the prominence of the blood vessels in the breast and the enlargement and darkening of the areola occur. All of these changes are in preparation for breastfeeding the baby after birth.

What happens to the breasts at menopause?

By the time a woman reaches her late 40s and early 50s, menopause is beginning or is well underway. At this time, the levels of estrogen and progesterone begin to fluctuate, with levels of estrogen dramatically decreasing. This leads to many of the symptoms commonly associated with menopause. With this reduction in the stimulation by estrogen to all tissues of the body, including the breast tissue, there is a reduction in the glandular tissue of the breasts. Without estrogen, the connective tissue of the breast becomes dehydrated and inelastic, and the breast tissue, which was prepared to make milk, shrinks and loses shape. This leads to the "sagging" of the breasts often associated with women of this age.

Women who are on hormone replacement therapy may experience some of the premenstrual breast symptoms that they experienced while they were still menstruating, which can even include tenderness and swelling. However, if there was sagging of the breasts before menopause, this is not reversed with hormone replacement therapy.

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