Female breast development seems to be one of those biological process that everyone gets to watch – after all, it’s not hard to notice prominent growths developing on half the human population – but no one seems to understand. Female breast development seems to be a mysterious process to almost everyone, even the young women undergoing the process, but it need not be. Breast development is thought to begin and end with puberty, but it is actually a fascinating, lifelong process.

Female breast development, though it starts in the womb, begins in earnest at the onset of puberty, which can be as early as nine years old in some girls. This means that, unlike other mammals, human females develop fully mature breasts long before they are needed for nursing. There are three phases of female breast development, and they are directly related to age. Lobule development takes places between the ages of 10 and 25; glandular development takes place under the influence of menstrual hormones between the ages of 13 and 45; and involution, or shrinkage of the milk ducts, starts at age 35.

The first inkling of human breast development begins about six weeks after conception with the appearance of a thickening called the mammary ridge or milk line. At six months, the ridge extends all the way down to the fetus’ groin, but it is starting a regression back up the fetal sternum. It contains several potential nipples, all but two of which will have disappeared by the time the ridge settles at the permanent location of the breasts. Occasionally, one nipple does not disappear, which is why some people have a third nipple. Once the nipples settle into place, female breast development, as opposed to general breast development begins. Solid columns of cells that will eventually be sweat glands begin to grow from each breast bud, and they each develop separate ducting leading to the nipple. By the final months of fetal development, the columns have become hollow, and when the baby girl is born, she is equipped with the beginnings of the milk-duct system.

Things are pretty quiet until the onset of puberty, when lobule development begins. At this time, the ovaries start to secrete estrogen, causing fat deposits on the connective tissues in the breast. The lactic duct system also begins to grow. The breasts begin to mature at the commencement of ovulation and menstruation when they form secretor glands at the ends of the milk ducts. The breasts and duct system will continue to mature and grow in size throughout puberty, forming many other glands and lobules.

There are outward changes that occur to the breast during puberty as well. First, breast buds appear as fat deposits accumulate on the glands and ductwork of the breasts. Both the breast and nipple are raised and the areola becomes darker. Then the breasts grow larger with the formation of glandular tissue, and the nipple and the areola form their own, secondary mound on top of the breast mound. Finally, as the breast matures, it becomes rounder and heavier, and only the nipple, not the areola, is raised.

A woman’s breasts don’t become fully mature until she gives birth and begins lactation. During pregnancy, in preparation for nursing, the breast forms many new glands and lobules. At this time, the areolas will darken and swell, followed by the swelling of the whole breast. After pregnancy, many women retain some of the increased breast growth, so the first pregnancy is sometimes thought of as a final growth spurt for the breasts.

Involution can start at around 35, but really becomes noticeable in a woman’s late 40s or early 50s, with the onset of menopause. With menopause, estrogen levels decrease, signaling to the breasts that they no longer need to prepare for breast feeding. Since there is no need to breast feed, the milk ducts and glands shrink, causing the breast itself to shrink. Also, lack of estrogen causes the connective tissue of the breast to become dehydrated and lose elasticity, causing the breasts to sag.

Female breast development is a lifelong process that women and men should both understand. Knowing how the breast develops helps de-mystify one of the most prominent parts of the human body and allows us to approach breast health and beauty in a sensible manner.

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