Pain and swelling are the body's way of signaling injury and tissue damage. Occasional breast swelling and tenderness is common with menses, or monthly uterine bleeding, and during times of hormonal imbalance such as menopause. However, armpit pain and swollen breasts could indicate a serious underlying medical condition and should not be ignored.
An infection of the breast tissues, mastitis is a painful condition usually involving one breast and the armpit. According to MedlinePlus, the bacteria causative of mastitis is a staph infection that invades the breast tissues by way of the nipple. Cracks, fissures and openings in the nipple allow infections, most commonly noted in breast-feeding mothers. A system of ducts within the breast leads milk from glands to the nipple for feeding infants. These ducts become compressed from inflammation due to mastitis, causing painful lactation, redness and a swollen breast. Severe armpit pain is possible on one side due to the lymph nodes within that armpit fighting and collecting debris from the infection.
Early Pregnancy Symptoms
Some women experience changes in the breast as early as 1 to 2 weeks following conception. The swelling in the breasts is not due to milk production, as lactation does not start until much later in pregnancy; it is indicative of hormonal changes throughout the body caused by the pregnancy. The breasts are innervated throughout the chest and armpits; highly sensitive breasts can reflect armpit pain. As opposed to other causes of armpit pain and swollen breasts, early pregnancy symptoms will show bilaterally, or in both breasts and armpits.
According to the National Breast Cancer Foundation, a doctor must evaluate any breast symptoms that do not spontaneously resolve. There are many different forms of breast cancer and a plethora of symptoms that indicate cancer. Swelling in the breast may be attributable to a lump or tumor within the breast. Monthly self-exams of the breasts will make a woman more familiar with any new irregularities in size, shape or texture of her breasts. In advanced breast cancers, lymphatic involvement is possible and can be reflected in hardened lumps or pain in the armpit. The armpit pain and breast symptoms occur on one side unless the cancer is present in both breasts.