Armpit pain is typically a sign of a strained muscle, minor infection, or skin condition. Occasionally, it can be a symptom of a more serious underlying condition, such as cancer. Some people may have rashes, boils, blisters, or sores on their skin, while others may have no visible symptoms.

Armpit pain is often a sign of overexertion or muscle strain. However, it can indicate an underlying condition, such as an infection, lupus, or shingles.

The armpit is the point where the muscles that move the arms and shoulders connect with the bones. Some of these muscles also connect to the ribs.

Major nerves and blood vessels also pass through the armpits, and each armpit is home to several lymph nodes. Swollen lymph nodes typically indicate that a person has an infection, but sometimes, they can be a sign of cancer.

The skin under the arms is thin and contains many sweat glands. The warm, moist conditions may increase the risk of fungal or bacterial infections or rashes due to chafing.

Healthcare professionals describe muscle strain as an injury to the muscles or tendons. The fibers in the muscles and tendons may overstretch or tear.

People taking part in sports and activities that involve lifting, pulling, or throwing may injure muscles and experience armpit pain.

Strained pectoral (chest) muscles, which people use for lifting and pulling, can often cause underarm pain.

Damage to the coracobrachialis muscle, or upper arm muscle, may also cause armpit pain. This muscle assists people in throwing and pushing motions.