Sore Armpit

Causes of a Sore Armpit

A swollen or sore armpit can be a painful and frightening condition. The entire armpit may feel sore, or you may have soreness in just one spot. Many people will feel these painful, hard lumps under the arm and be afraid that it is a cancerous growth. However, there are several causes for painful swelling or lumps under the arms that are no cause for alarm, including swollen lymph nodes or infection.  

The most common cause of a sore armpit is a swollen lymph node. The body has a lymphatic system, which is part of the body’s immune system of fighting disease. The lymphatic system is made up of many lymph nodes in the neck, under the jaw, groin and under the arms. The lymph nodes can become swollen due to infections, autoimmune disorders, or cancer. Commonly, the lymph nodes under the arms become swollen or sore due to infection. If other lymph nodes, such as the nodes behind your ears on under the jaw, are swollen as well as the nodes under your armpit, you may have an infection. See your doctor for a diagnosis and antibiotics to treat swollen lymph nodes.


If you do not have swollen lymph nodes, a swollen or sore armpit may be caused by an infection in the layers of skin, sometimes called cellulitis. People get these infections frequently under their arms from nicks caused by shaving. If you shave under your arms, you may nick yourself, causing a small cut. Bacteria can then enter the skin through the cut and cause an infection. Infections under the arm can be very painful and result in red, swollen tissue. You can try treating the infection with over the counter antibacterial cream, but if it persists or gets worse, see your doctor.

Some infections can turn into abscesses. An abscess is a type of localized infection that causes a collection of pus. The area around the abscess is usually inflamed or and swollen and may be painful. Abscesses happen when the immune system tries to fight an infection by sealing off the area and flooding it with white blood cells. There is a buildup of fluid, which flushes out the bacteria causing the infection as well as dead tissue and white blood cells. Heat is commonly used when an abscess is present under the skin. For an abscess under the arm, soak a small towel or wash cloth in hot water and press to the affected area. This may relieve some pain and help speed healing.

If you are a new mother who is breastfeeding, you may also suffer from sore or swollen armpits. Breast tissue reaches all the way back into the armpits. When breastfeeding, your milk ducts may become blocked and prone to infection. If the breast tissue under the arms is swollen or painful, a blocked or infected milk duct could be the culprit. Warm compresses under the arm can help ease the pain of swollen breast tissue. As with any painful condition, you should always see your doctor for a diagnosis.

If you are suffering from a sore or swollen armpit, always see your doctor for a professional diagnosis and treatment options. If you have an infection in your lymph nodes, your doctor can prescribe antibiotic medicines to help clear it up. Doctors will usually drain more severe infections like abscesses, or prescribe topical antibiotic cream to combat skin infections under the arms. With proper treatment, a sore armpit due to infection can be cured in a matter of days.