In order to understand the often bewildering textures and changes that the human breast
undergoes in normal and especially abnormal situations, it is necessary to learn about
what the breast is made of and what it is influenced by.
Breasts begin developing in the embryo about 7 to 8 weeks after conception. They are
unrecognizable at this stage consisting only of a thickening or ridge of tissue. From
weeks 12 to 16, the various sub-components become more defined. Tiny groupings of cells
begin to branch out laying the foundation for future ducts and milk producing glands.
Other tissues develop into muscle cells which will form the nipple (the protruding
point of the breast) and areola (the darkened tissue surrounding the nipple). In
the later stages of pregnancy, the mother's hormones, which cross the placenta into the
fetus, cause breast cells to organize into branching tube-like structures thus forming the
milk ducts. In the final 8 weeks, lobules, (milk producing glands), mature
and actually begin to secrete a liquid substance called colostrum. In both female and male
newborns, swellings underneath the nipples and areolae can easily be felt and a clear
liquid discharge, colostrum or "witch's milk", can be seen. These represent the
effect of the mother's hormones and subside in the first few weeks of life.
From infancy to just before puberty, there is no difference between the female and male
breasts. With the beginning of female puberty, however, the release of estrogen, at first
alone, and then in combination with progesterone when the ovaries functionally mature,
cause the breasts to undergo dramatic changes which culminate in the fully mature form.
This process on average takes 3 to 4 years and is usually complete by age 16. Further
maturation of the breast tissues occurs with lactation and is felt to be mildly protective
against breast cancer.
mature female breast is composed of essentially four structures: lobules or glands;
milk ducts; fat and connective tissue (see diagram). The lobules group
together into larger units called lobes. On average there are 15-20 lobes in each
breast arranged roughly in a wheel spoke pattern emanating from the nipple/areolar area.
The distribution of the lobes is not even, however. There is a preponderance of glandular
tissue in the upper outer portion of the breast. This is responsible for the tenderness in
this region that many women experience prior to their menstrual cycle. It is also the site
of half of all breast cancers. The lobes empty into the milk ducts which course through
the breast towards the nipple/areolar area. There, they converge into 6-10 larger ducts
called collecting ducts which enter the base of the nipple and connect with the
outside. During lactation (breast feeding), the breast milk follows this course on
its way to the feeding infant.
The consistency of breast lobes vary from woman to woman and may even vary in an
individual from one side to the other. However, in general, the glandular portion of the
breast has a firm, slightly nodular feel to it. Surrounding the lobes is breast fat.
Unlike the lobes, the fat is almost always soft. The discrepancy in textures between these
two components allows one to outline the lobes by carefully palpating (feeling) the
breast. Interestingly, the difference in density between glandular breast tissue and
breast fat is also the basis for mammographic imaging. In contrast, the ducts of the
breast are usually not palpable unless they are engorged with milk, inflamed or contain a
The breasts of younger women are primarily composed of glandular tissue with only a
small percentage being fat. Thus they are firmer than in older counterparts. As women age,
especially with the loss of estrogen at menopause, the lobes involute (shrivel) and
are replaced by fat. The breasts become softer and lose their support. Physical
examination and mammography are easier to interpret and may well be more accurate.
Whereas all components of the breast are influenced by female hormones, the glandular
tissue is most sensitive. Very dramatic and totally normal changes can occur in the
consistency of the breasts during the menstrual cycle. These changes are most evident just
prior to menstruation when levels of estrogen and progesterone are peaking. Right after
menstruation, hormone levels are at their lowest and the breast becomes softer and less
tender. This is the recommended time to perform breast self-examination, BSE, and to have
In post menopausal women, who are not taking estrogen supplementation, weight becomes a
significant factor in the size and appearance of the breasts. Being mostly composed of fat
at this point, small changes in body weight can produce significant changes in breast
There are several, well described congenital (present from birth) abnormalities
of the breast, which are worth mentioning. The most common of these are accessory nipples
and/or breast tissue. This occurs in 2-6% of the population and often goes unrecognized.
Accessory nipples are seen anywhere along the milk line (a ridge of tissue, present
only in the fetus, extending from the underarm to the groin from which breasts develop).
They are frequently multiple. Accessory breast tissue can also be found in this
distribution but most often occurs in the underarm area. There is no special clinical
importance to these other than being aware of their presence and including them in
Severe underdevelopment or absence of one or both breasts is another congenital
abnormality that can occur. Unlike accessory nipples and breast tissue, this defect is
extremely rare. Usually a rudimentary nipple is present on the effected side in these
individuals. Coexisting abnormalities of the underlying muscles and rib cage are common.
Plastic surgical correction is possible and often provides significant improvement in
quality of life.
For more information see Beth Israel's Patient's Guide to Breast Cancer
Back To Top
Return to homepage