Armpit or underarm pain can be caused by numerous conditions. According to the U.S. National Library of Medicine and the National Institutes of Health or NIH, the underarm is a common location for bacterial infection, although other conditions--including nerve- and blood vessel-related conditions--can also cause pain in this region. Underarm pain ranges from mild to severe, depending on the type of injury or condition.
Brachial Plexus Injury
Brachial plexus injuries can cause underarm pain. According to the National Institute of Neurological Disorders and Stroke--or NINDS, a division of the National Institutes of Health--brachial plexus injuries are caused by damage, often due to traction, to the network of nerves that transmit electrical signals from the central nervous system or brain and spinal cord to structures in the upper extremity. This network of nerves, which courses through the armpit, is called the brachial plexus. Common signs and symptoms associated with brachial plexus injuries include an electric shock or burning sensation, also known as a stinger that shoots down the arm, numbness, tingling and weakness in the upper extremity and, in severe cases, an inability to use the affected-side arm or fingers. The NINDS states that the severity of a brachial plexus injury is governed by the type of damage done to the nerves.
Peripheral Arterial Disease
Peripheral arterial disease can cause underarm pain. The Baylor College of Medicine's Michael E. DeBakey Department of Surgery states that arm artery disease is an uncommon type of peripheral arterial disease in which one or more of the arteries between the chest and the hand becomes obstructed or blocked. Upper extremity peripheral arterial disease may affect the large arteries that course through the armpit into the upper arm, along with smaller arteries in the forearm and hand. Upper extremity peripheral arterial disease usually affects cigarette smokers and people over the age of 65. Common signs and symptoms associated with upper extremity peripheral arterial disease include pain or discomfort, heaviness, tiredness or cramping in the affected armpit and arm, muscle wasting, a faint or absent pulse, bluish skin discoloration in the affected area and cold intolerance. One of the most common causes of peripheral arterial disease is atherosclerosis or the hardening and blockage of arteries.
Breast Infection
A breast infection can cause underarm pain. According to the National Institutes of Health, or NIH, breast infections are usually caused by bacterial invasions of the breast tissue. The most common bacterial agent associated with breast infections is Staphylococcus aureus. Staphylococcus aureus enters the breast through a break in the skin, usually in the nipple, and causes swelling in the breast's fatty tissue. The infection-induced breast swelling places pressure on the milk ducts, which causes pain and lumps in the infected breast. The NIH notes that breast infections are particularly common among mothers who are breast-feeding their infants. Common signs and symptoms associated with breast infections include tender and enlarged lymph nodes in the armpit, one-sided breast enlargement, breast pain, nipple discharge, fever, itching and breast swelling, warmth and redness.
