Normal Breast Development and Changes
What is normal breast development?
Breast development happens in distinct stages throughout a woman's life, first before
birth, again at puberty, and during the childbearing years. Changes also happen to
the breasts during the menstrual cycle and when a woman reaches menopause.
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, nipples
and the beginnings of the milk-duct system have formed.
Breast changes continue to happen over the lifespan, with lobes, or small subdivisions
of breast tissue, developing first. Mammary glands develop next and consist of 15
to 24 lobes. Mammary glands are influenced by hormones activated in puberty. Involution
or shrinkage of the milk ducts is the final major change that happens within the breast
tissue. A gradual shrinking of the mammary glands (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 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.
Female breast developmental stages
(Preadolescent) only the tip of the nipple is raised
Buds appear, breast and nipple raised, and the areola (dark area of skin that surrounds
the nipple) enlarges
Breasts are slightly larger with glandular breast tissue present
The areola and nipple become raised and form a second mound above the rest of the
Mature adult breast; the breast becomes rounded and only the nipple is raised
What cyclical changes happen to the breasts during the menstrual cycle?
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. Next, 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, like
the swelling, pain, and tenderness that many women experience in their breasts just
During menstruation, many women also experience changes in breast texture. Breasts
feel particularly lumpy. These are the glands in the breast enlarging to prepare for
a possible pregnancy. If pregnancy does not happen, the breasts return to normal size.
Once menstruation begins, the cycle begins again.
What happens to the breasts during pregnancy and lactation?
Many healthcare providers believe the breasts are not fully mature until a woman has
given birth and made milk. Breast changes are one of the earliest signs of pregnancy.
This is a result of the 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. This is because
of the growth of the milk duct system and the formation of 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, like follicle-stimulating hormone
(FSH), luteinizing hormone (LH), prolactin, oxytocin, and human placental lactogen
(HPL) also play vital roles in milk production.
Other physical changes, like the prominence of the blood vessels in the breast and
the enlargement and darkening of the areola happen. 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.
The levels of estrogen dramatically decrease. 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. 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 taking hormone therapy may experience some of the premenstrual breast
symptoms that they experienced while they were still menstruating, like tenderness
and swelling. However, if there was sagging of the breasts before menopause, this
is not reversed with hormone therapy.