Mammary Glands and Mastitis

by Robert Tallitsch, PhD | April 18, 2023

Video explaining mammary glands and mastitis using a real patient imaging!

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Written by: Robert Tallitsch, PhD

Female Mammary Glands and Mastitis

“Do I or don’t I breastfeed my baby?” The CDC indicates that slightly over 83% of infants were breastfed for at least the first six months of their lives in 2020 – 2021. The CDC also indicates that approximately 10% of breastfeeding mothers develop lactation mastitis — an uncomfortable and often painful inflammation (swelling) of the breast. This Brain Builder will discuss the anatomy of the breast and how that anatomy changes during pregnancy. This will be followed by a discussion of the causes, symptoms, and treatment of mastitis.

Anatomy of the Female Mammary Gland (Breast)

The anatomy of the mammary gland (breast) is typically studied when anatomy students are dissecting the axilla (armpit), in that the arterial supply, venous, and lymphatic drainage of the breast are associated with the axillary vasculature. Blood supplying the lateral mammary glandular tissue comes from the lateral thoracic branch of the axillary artery. The medial glandular tissue is supplied by the internal thoracic artery. Most of the venous and lymphatic drainage of the breast is directed towards the axillary region.

Prior to Pregnancy

In the adult female most of the central portion of the mammary gland overlies the pectoralis major and serratus anterior muscles of the anterior thoracic wall. A layer of deep fascia separates these muscles from the more superficial glandular tissue of the mammary gland.

Mammary glands are modified sweat glands of the skin. (Want to know more about glands of the skin? Check out our Brain Builder “Glands of the Skin and Acne”.) Internally the glands are composed of secretory lobules and associated ducts. The secretory ducts converge to form between fifteen and twenty lactiferous ducts, all of which open independently at the nipple of the breast. Surrounding the nipple of the breast is the areola — a pigmented, circular area of skin.

A well-developed connective tissue stroma is found in between the secretory lobules and ducts of the breast. Suspensory ligaments, which are composed of dense connective tissue within the breasts, connect to the dermis of the skin deep to the mammary glands. These ligaments provide support for the breast.

In a nonlactating female the primary component of the breast is adipose tissue.

Changes During Pregnancy and Breast Feeding

Changes in hormonal levels during pregnancy significantly alter the internal anatomy of the female breast, and these changes start to occur almost on day one of pregnancy.

With the onset of pregnancy blood flow to and fluid retention within the breast increases significantly, often causing sensitivity to touch and the sensations of swelling and soreness.

At approximately six or eight weeks of pregnancy the breasts will begin to increase in size and will continue to do so throughout pregnancy. Soreness and sensitivity to touch will increase at this time as well.

The nipple and areola may become darker in color, which is due to the continued increase in blood flow to the breasts.

At approximately the third or fourth month of pregnancy women may notice some or all of the following:

  • Small bumps appear in the areola of the breast. These bumps are the result of the development of small oil glands in the areola.
  • The size and extent of the nipples may increase.
  • The circumference of the areola will increase.
  • The breasts of some women may begin to leak colostrum (also termed premilk), which is a thick, yellowish substance. However, this may occur later in some women, or not at all in others.

As the mother nears the delivery date the composition of the colostrum changes from thick and colored to a less-dense fluid that is quite pale in color.

Lactational Mastitis


Signs and symptoms of mastitis can, and often do, occur suddenly. The breast swells, becomes tender and warm to the touch. The skin of the breast becomes red, and often displays a wedge-shaped pattern to the coloration. The skin of the breast may appear thicker, and a palpable lump may be noticed within the breast. In addition, pain and/or a burning sensation may be felt by the mother during breast feeding. A fever at or above 101° F (38° C) is not uncommon.


The trapping of milk within the breast, due to a clogged secretory or lactiferous duct, is the most common cause of mastitis. Another cause of mastitis is the introduction of bacteria into the breast through the nipple. Most often the bacteria are introduced into the breast from either the baby’s mouth or the skin of the mother. The bacteria then interact with any stagnant milk within the breast, initiating the infection.


Because a rare form of breast cancer, termed inflammatory breast cancer, can present with symptoms like lactational mastitis, a complete and thorough physical exam will be undertaken. Often a culture of breast milk will be obtained and analyzed, which will enable the physician to prescribe the best form of antibiotic to combat the infection within the breast.


Treatment of mastitis often includes the prescription of antibiotics and pain relievers. Almost all of the time it is safe for both the mother and infant to continue breastfeeding. In addition, the physician may refer the mother to a lactation consultant to work with the mother to adjust her breast-feeding techniques in order to minimize the possibility of another case of mastitis.

Non-lactational Mastitis

Although it is extremely rare, non-lactational mastitis can occur. This condition is a benign, inflammatory condition of the female breast in a woman that is not lactating. This condition involves an inflammation of the lactiferous ducts, and may result in fibrosis, fistulas, abscesses, and scarring of the duct structure of the breast. Treatment of non-lactational mastitis is often similar to that of lactational mastitis.

In most cases a proper diagnosis followed by quick treatment with antibiotics results in the elimination of lactational mastitis with few, if any long-term effects for either the mother or the infant.


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