The female breast may be a symbol of beauty and intimacy. It provides nourishment to infants. But scientifically, it is a modified sweat gland. It is composed mainly of fat and glandular tissue. Breast size, shape, and health depend on many things. These include genetics, hormones, environment, and lifestyle. Genetics greatly influence breast appearance and health. If your genes say you will have large breasts, you probably will. You can influence your hormone levels to some extent. You can do this by managing your environment and lifestyle.
Budding Breasts
Breast development in women begins very early. It begins in the womb, about 6 weeks after conception. As the fetus grows, hormones prepare for breast development. Estrogen helps the ducts in the breasts grow. Estrogen and progesterone together help develop milk-producing glands. These glands are called lobular glands. At the same time, the mother's hormones support breast development. These hormones include insulin and adrenal steroids. Growth hormone and prolactin also play a role. Thyroid-stimulating hormone and luteinizing hormone are also important.
The mammary gland is the first part of the breast to develop. A set of glands develops from the groin to the armpit area. This is called the "milk ridge." By 9 weeks of pregnancy, most of this ridge disappears. Only one pair of glands remains. These will become the breasts. Sometimes, extra glands remain along the ridge. Then, a baby may be born with an extra nipple. This condition is called polymastia. It often looks like a mole.
Puberty
Newborns may have a slight nipple discharge, called "witch's milk." This occurs in most babies for a few days after birth. After that, breast development stops until about 10 to 12 years. Then, estrogen levels increase. This triggers hormone receptors in the breasts. These receptors then stimulate milk gland growth. Some girls feel itching or slight pain under the nipple. This early sign of puberty usually occurs before the first period.
When menstruation begins, usually between the ages of 11 and 15, the breasts respond to hormones. These hormones come from the brain, adrenal glands, and ovaries. Breast tenderness and swelling are common at this time.
Reproductive years
Breasts link to changing menstrual cycles. When a young woman starts her period, hormones get involved. Follicle-stimulating hormone (FSH), estrogen, luteinizing hormone (LH), and progesterone all play a role. They prepare the breasts in case she can breastfeed. In the first half of the cycle, about 14 days before an egg is released, the pituitary gland sends out FSH. FSH tells the follicles to make estrogen. Follicles are sacs on the ovaries that contain the eggs. As estrogen in the blood rises, the milk glands swell. This makes the breasts bigger and firmer. When estrogen is high enough, FSH stops, and LH takes over. Estrogen and LH start ovulation. This is when a follicle releases a mature egg. The second half of the cycle then begins. The egg moves down the fallopian tube, hoping for a pregnancy. The ovaries make progesterone during this time. Progesterone sets the breasts up for breastfeeding. It also changes the uterine lining. The lining becomes rich with blood and tissue for the egg.
Estrogen and progesterone together affect the breasts the most. They cause more ductal and lobular tissue to grow. These changes cause breast tenderness and swelling. Many women feel this during their cycle. They may also feel lumps in their breasts in the second half of the cycle. This is often normal. To ease fears about these lumps, check your breasts often during your cycle. If lumps seem normal in the second half, they likely are pregnancies. If the egg is not fertilized, estrogen and progesterone drop. Then, menstruation begins. Without high hormone levels, breast swelling, tenderness, and lumps go away. But, if pregnancy occurs, the breasts change to prepare for breastfeeding.
Perimenopause and menopause
Most women notice a change in periods in their late 30s or early 40s. Estrogen and progesterone levels drop at this time. This is known as perimenopause. The supply of follicles inside is reduced. They can't make enough estrogen to keep periods regular. As periods become less frequent, other body changes occur. These include breast soreness and lumps or cysts in the breasts. Most lumps are not harmful. They occur because breast tissue changes during this life stage.
Other symptoms of perimenopause are dry skin, hot flashes and back pain. Some women skip this stage and go into menopause. Menopause is when periods stop completely. Unless hormone therapy is used, the big drop in estrogen and progesterone makes breast tissue soft and thin. Fat takes over again. Eventually, the follicles stop making estrogen altogether. The adrenal gland then produces androgens, which turn into estrogen. This gland makes a small amount of estrogen. At about age 70, this backup estrogen supply also runs out.
