Less commonly, the pain—referred to as axillary pain—may be due to an autoimmune or arterial disease, nerve compression, and ...

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.

Other causes of an armpit rash include a yeast infection, psoriasis, or seborrheic dermatitis. Rashes are pesky patches of irritated skin that can affect any part of your body, including your armpits.