There are many possible causes of underarm breast pain. Among them are cysts, breast cancer, and infection. In some cases, underarm breast pain may develop in relation to a woman’s menstrual cycle or due to clogged milk ducts in a woman who has given birth to a child. Sometimes pregnant women may also experience tenderness and swelling in this area as a normal pregnancy symptom. A rash, friction from clothing that rubs the skin, and even something as simple as an overly tight bra may cause this issue as well.

One of the most common causes of underarm breast pain is some sort of lump. A lump that develops in this area is an abnormal growth that may be hard, rubbery, immobile, or mobile. In some cases, a lump that causes underarm breast pain may be a benign cyst or other type of non-cancerous growth. In others, however, underarm breast pain may develop as a symptom of a cancerous breast lump.

Sometimes underarm breast pain may develop as the result of hormonal or physical changes in a woman’s body. For example, some women experience breast tenderness, including in the underarm region, in relation to their menstrual cycles. In such a case, a woman’s breast pain may develop because of changes in the levels of progesterone and estrogen in her body. When breast pain is related to a woman’s menstrual cycle, it is often referred to as cyclic breast pain.

In some cases, a woman may experience underarm breast pain that develops because of pregnancy. As with menstruation, pregnancy is marked by changes in the levels of progesterone and estrogen in a woman’s body. The pain or tenderness a woman may feel under her underarm area may develop as a result of these hormonal changes. Additionally, most women experience breast growth during pregnancy, and this may be accompanied by pain and tenderness as well. Often, the pain is at its worst during the first trimester of pregnancy.

Underarm breast tenderness may frequently develop as a sign that something is wrong. Besides cancer, other issues such as infection, clogged milk ducts, and skin rashes may cause pain in this area. A woman may note pain in the underarm region as a result of friction caused by her clothing as well. In some cases, something as simple as a very tight bra may cause soreness or pain. Additionally, trauma or injury to the breast tissue may cause pain in this area as well.