The Anatomy of the Mammary Glands

Responsible for Lactation

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Mammary glands are found in the breasts of humans and other mammals. Regulated by the endocrine system, mammary glands respond to the hormonal changes that take place during pregnancy and following birth. The mammary glands are responsible for lactation, also known as milk production.

Breast cancer, which most often forms in the mammary glands or breast ducts, is the biggest threat to breast health. Statistically, 1 in 8 people with breasts will develop breast cancer in their lifetime. Other conditions that can affect the mammary glands include mastitis, cysts, lumps, and ectasia.

X-ray image of the breast, showing the internal breast in bright, neon colors

Science Photo Library - ROGER HARRIS / Getty Images


Ventral epidermal ridges, also known as milk lines, are precursors to the mammary glands and nipples. The mammary glands are located in the breast. They develop in pairs from modified sweat glands.

Mammary glands are present in all people at birth, regardless of gender assignment. But only those who have a surge in estrogen during puberty will have fully developed mammary glands and breasts. Those with a surge of testosterone during puberty will have underdeveloped mammary glands and will not develop breasts.

The external breast has a raised nipple and the surrounding darkened area, called the areola. Internally, the breast holds 15-20 lobes of glandular tissue that branch out in a circle from the nipple.

Milk ducts collect milk from the small sections of tissue found inside the lobes, called lobules. At the nipple, the milk ducts enlarge for milk to collect, then narrow again, where each duct opens independently on the nipple.


Hormones play an essential role in facilitating the primary function of the mammary glands, milk production.

Estrogen plays a role in expanding milk ducts, causing them to branch out to hold more milk. During puberty, estrogen and growth hormones cause the mammary glands to develop and grow. In pregnancy, as estrogen and progesterone increase, the milk ducts grow, and the breasts enlarge.

Prolactin contributes to the development of mammary glands and the production of milk. Progesterone helps lobules grow in preparation for lactation and also enlarges blood vessels in the breast after ovulation, which contributes to breast swelling and tenderness. Oxytocin causes milk to eject from the glands.

With the decrease in the production of estrogen around menopause, mammary glands shrink, causing breasts to appear softer and less full with age

Associated Conditions 

Breast Cancer

Female breast cancer is one of the most common cancers, affecting 1 in 8 women. People who have removed their breasts for any reason (including top surgery or prophylactic mastectomy) have lower risk than cisgender women.

Hormone therapy may alter the risk of breast cancer Breast cancer in cisgender men and transfeminine people not on hormone therapy is much rarer but does occur. Transmasculine people who were on puberty blockers will have a level of breast cancer risk similar to cisgender men and transfeminine people not on gender-affirming hormone therapy. 

Breast cancer can start from multiple locations in the breast, including the mammary glands, milk ducts, and other tissues. Left undetected, breast cancer can spread to other organs through the blood and lymph node system.


Mammary duct ectasia most commonly occurs near or after menopause. Ectasia is a noncancerous thickening of the milk ducts. It does not always cause symptoms, but sometimes can present as breast pain and swelling, nipple discharge, or a nipple that pulls inward.

Ectasia does not always require treatment, but sometimes antibiotics or surgical removal of the duct may be required.


Fluid-filled cysts in the breasts are usually benign. Breast cysts develop in milk ducts and are fairly common in later childbearing years. About 1 in 4 breast lumps are cysts. It is unknown what causes cysts, but they may develop as a result of hormonal fluctuations.

Fibrocystic Breast Changes

In addition to tumors and cysts, lumps in the breast can indicate fibrocystic breast changes. Fibrocystic breast change is a common, benign condition that affects people primarily before menopause. It is characterized by lumpy breast tissue.

This condition was formerly referred to as fibrocystic breast disease, but most clinicians have dropped the term “disease” in favor of “changes” since it is not actually a disease.


Mastitis is an infection that occurs in the breast tissue. It most commonly affects women who are breastfeeding. Mastitis is caused by bacteria that enter the breast through a milk duct or a crack in the skin.

Mastitis symptoms include breast swelling, tenderness, redness, fever, and flu-like muscle aches. At-home treatment usually resolves mastitis, but some cases may require antibiotics. 

Breast Pain

Breast pain can happen as a result of a number of things, including cysts, hormonal fluctuations, pregnancy, infection, breastfeeding, and sometimes cancer. Depending on the cause, breast pain can often be managed at home. It is important, however, to have persistent or severe pain and all lumps evaluated by a healthcare provider. 


Clinical breast exams and self-exams used to be considered a gold standard for early detection of breast cancer. But more recently, the American Cancer Society (ACS) and the Centers for Disease Control and Prevention (CDC) have stopped recommending them because of the lack of evidence that they find breast cancer early.

Even without monthly self-breast exams, most people are familiar with their breasts and often notice changes or lumps through normal activities like showering or changing clothes. In such a case, a clinical breast exam is often performed.

During a clinical breast exam, a healthcare provider examines the breast’s appearance and palpates the breast with their fingertips to feel for any abnormalities.

Mammograms are X-rays of the breast. During a mammogram, you will stand in front of a specialized X-ray machine. A technician will place your breast on a plate, then bring another plate down to flatten the breast. Finally, the technician will take a picture of your breast. This will be repeated from the top and the side on both breasts.

A mammogram may be recommended to identify a lump that you or your healthcare provider have detected in your breast. They are also used as a screening tool to detect breast cancer.

The American College of Obstetriciansand Gynecologists recommends that women at average risk of breast cancer get a mammogram every one to two years beginning at age 40, and no later than 50; screening should continue until at least age 75 years.

Biopsies of the breast may be done when a small sample is required for laboratory testing. Needle biopsies are done by inserting a needle into the breast to extract fluid or cells (known as fine needle aspiration), or by using a larger, hollow needle to extract small amounts of tissue samples (known as core needle biopsy).

Sometimes ultrasound or MRI is used for guidance. If a larger section of tissue or mass needs to be removed or assessed, a surgical biopsy, also known as an incisional biopsy, might be recommended. 

9 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. National Cancer Institute. Mammary glands.

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By Kathi Valeii
As a freelance writer, Kathi has experience writing both reported features and essays for national publications on the topics of healthcare, advocacy, and education. The bulk of her work centers on parenting, education, health, and social justice.