Hormonal changes, including those related to menstruation or breastfeeding, also may cause pain under the armpit (also called ...

A hiatal hernia – a rarer cause of pain under your left breast—is when your upper stomach bulges through the diaphragm, which separates your abdomen and chest, per Mayo Clinic. The painful sensation ...

A male breast lump does not always mean cancer, but it’s important to know the symptoms and characteristics to look out for.