Cysts (fluid-filled tissue pockets), infections, and swollen lymph nodes commonly cause armpit lumps. Finding a lump in your armpit can be worrisome, especially if it hurts or appears unexpectedly.

Painful armpit lumps are often due to a swollen axillary lymph node under the armpit. This is usually a sign that the body is fighting an infection, but it can sometimes indicate cancer.

Lymph nodes are part of the body’s immune system. A swollen lymph node in the armpit may be a sign of a bacterial or viral infection, an injury, or a serious health condition, such as cancer.

Medically reviewed by John Carew, MD A lump on the side of the neck could be a swollen lymph node caused by a bacterial or ...