Breast development occurs in stages, beginning before birth, changing during puberty and the childbearing years, and ending at menopause.
Breasts can grow in response to hormones estrogen and progesterone, as well as pathological conditions such as benign and cancerous breast tumors and certain medications.
Breast changes continue to occur throughout a woman’s life. The first thing to develop are lobes, followed by mammary glands, which are influenced by hormones activated in puberty. Shrinkage of the milk ducts is the final major change that occurs in the breast tissue, which typically starts at about age 35.
What are the physiological causes of breast growth?
Puberty
As a girl approaches her teen years, the first visible signs of breast development begin. When the ovaries start to produce and release estrogen, fat in the connective tissue starts to collect, causing the breasts to enlarge. The duct system starts to grow. Often, these breast changes occur at the same time pubic and armpit hair appear.
Once ovulation and menstruation begin, 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 glands and lobules. The rate at which breasts grow is different for each person.
Menstrual cycle
Each month, women go through hormonal changes during the menstrual cycle. The hormone estrogen is produced by the ovaries in the first half of the menstrual cycle and stimulates the growth of milk ducts in the breasts. Increased levels of estrogen lead to ovulation halfway through the cycle. Progesterone then takes over in the second half of the cycle and stimulates the formation of the milk glands. Progesterone is responsible for cyclical changes that many women feel in their breasts just before menstruation, such as swelling, pain, and soreness.
During menstruation, many women have changes in breast texture. For example, their breasts may feel lumpy, because the glands in the breast are enlarging to get ready for a possible pregnancy. If pregnancy does not occur, breast size goes back to normal. Once menstruation starts, the cycle begins again.
Pregnancy and lactation
Many doctors believe the breasts are not fully mature until a woman has given birth and produces milk. Breast changes are one of the earliest signs of pregnancy caused by progesterone. For example the dark areas of skin around the nipples (areolas) may begin to swell. This is followed by rapid swelling and expansion of the breasts. Most pregnant women feel soreness down the sides of the breasts and tingling or soreness in the nipples because of the growth of the milk duct system and formation of many more lobules.
By months 5 or 6 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 play vital roles in milk production. These include follicle-stimulating hormone, luteinizing hormone, prolactin, oxytocin, and human placental lactogen.
Other physical changes may also occur, such as the blood vessels in the breast becoming more visible and areolas getting larger and darker. All these changes are in preparation for breastfeeding the baby after birth.
Menopause
Perimenopause typically starts or is underway by the time a woman reaches her late 40s and early 50s. At this time, estrogen and progesterone levels begin to change. Estrogen levels dramatically decrease, leading to many of the symptoms commonly linked to menopause. Without estrogen, the breast’s connective tissue becomes dehydrated and is no longer elastic. Breast tissue begins to shrink and lose shape.
Women who undergo hormone therapy may have symptoms similar to menstruation symptoms such as breasts soreness and swelling. However, if a woman’s breasts were saggy before menopause, this will not change with hormone therapy.
Weight gain
Because most breast tissue is made up of fats, an increase in body fat leads to accumulation of fats in the breasts, giving them a fuller appearance. Therefore, if increased food or calorie intake may result in the enlargement of one’s breast.