Underarm Breast Tissue

It is hard not to think about a woman’s breasts as two hemispheres attached to her upper chest. That is the way society tends to show them in film, TV, and advertising. It is the way most push-up bras can make breast look.

Breasts, as any woman who has a pair will tell you, are usually not perfect hemispheres. They can often be sort of teardrop shaped or bell shaped.

But did you know that for some women part of each breast can be located under her arm, in the armpit? Anywhere from two percent to six percent of woman have some breast tissue under the arm. What may be more startling is that this breast tissue can start to make milk after you give birth and start breastfeeding.

In other words, you may have milk coming out of your armpit when you start breastfeeding.

There are several names for breast tissue in the armpit. It is often called axillary breast tissue since the medical word for your underarm is the axilla. It is also called the Spence tail or a tail of Spence, named after the doctor who first described it. Having axillary breast tissue tends to run in families.

Having breast tissue in the area under your arms is perfectly normal. This breast tissue will usually be located toward the front of the armpit and is an extension of the upper outside quadrant of each breast. Most women who have axillary breast tissue think that it is fat and may try to diet or exercise it away, which won’t work because it is neither fat nor muscle.

When a woman is not pregnant or breastfeeding, this breast tissue may not be noticeable at all. During late pregnancy, axillary breast tissue may start enlarging and become more prominent when the rest of the breast enlarges. It may become more visible or make wearing a bra uncomfortable.

Women who have axillary breast tissue may never have a problem with it. The breast tissue they have under their arms may develop one or more milk ducts that lead to the nipple. This duct allows milk from that portion of the breast to reach the nipple along with the milk from the rest of the breast. The baby feeds normally and the axillary breast tissue drains well.

But sometimes milk ducts don’t develop or don’t connect to the nipple. The breast tissue under the arm makes milk, but the milk doesn’t have anywhere to go. The area may become engorged and feel hot and tender. Mastitis, which is an inflammation of breast tissue, can develop. In a worst-case scenario, the engorged tissue can become infected, and an abscess can form.

The treatment for engorged axillary breast tissue is cool compresses, but you should also seek advice from your doctor or midwife or from a lactation consultant. If the area becomes very sore and hot and if you develop a fever, call your healthcare professional immediately.

If a milk duct doesn’t develop and this area becomes engorged, breast milk may start to seep through the skin. A case report in the journal Mayo Clinic Proceedings discussed the case of a young woman who was able to pump milk from the engorged axillary breast tissue through her skin successfully. Other women have reported milk leaking out under one or both arms.

Axillary breast tissue is not the same thing as having an extra breast, which is seen on rare occasions. Breasts form in a human embryo or fetus along two lines of tissue called the milk lines or mammary ridges which run from the groin to the armpit. This tissue starts to shrink before birth and normally only two breasts are formed, but rare individuals develop more than two with the extra breasts being located along the milk lines.

Some people, both men and women, can also have an extra nipple, which may be small and often is thought to be a mole. Only during pregnancy, when the “mole” starts to enlarge does it start to look more like a nipple and may produce milk.

Just like the tissue in the rest of your breasts, the breast tissue under your arm can become cancerous. However, it is not any more likely to become cancerous than the rest of your breast. If you know you have axillary breast tissue, make sure to mention this when you have a mammogram done so that the technician makes sure to include the area in the imaging.

Axillary breast tissue generally doesn’t cause any problems and does not need to be removed, but it can be if you don’t like the look of it. Some women may want the area under their arms to look sleeker and smoother and choose to have axillary breast tissue removed through cosmetic surgery or liposuction.

Valerie DeBenedette
Valerie DeBenedette is an experienced health and medical writer who lives about an hour north of New York City with a dog that is smaller than her cat. Her work has appeared in magazines, newspapers, newsletters, and on websites. She is a member of the National Association of Science Writers.

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