Bumps under the arms usually are due to an enlargement of the lymph nodes that reside there. The lymph nodes are organs that trap infectious materials or cells. According to Medline Plus, bumps under the arm can be caused by any number of factors, including cysts, abscesses or tumors.
Diagnosis
When you feel a bump under your arm, have it checked out by a physician who will examine the lump and gently press the area to gauge its size and composition. Tests that can determine the cause of the bump include blood tests, a mammogram, a chest X-ray, liver- and kidney-function tests and a liver-spleen scan. A biopsy of the tissue may be taken to determine if the lump contains cancer cells.
Causes
A bump may be the result of a bacterial or viral infection. Shingles, AIDS and chicken pox often produce bumps under the arms. Lipomas are benign fatty growths that develop under the arms for no apparent reason, and breast tissue may spread to the area and cause a fatty deposit, according to the University of Texas Medical Center. Hodgkin's and non-Hodgkin's lymphoma, leukemia and breast cancer all start out as malignant growths that typically first appear as a bump under the arm.
Risk Factors
Nearly one in eight women will get breast cancer that starts as a small lump under the arm. Women are 100 times more at risk for developing the disease and women over the age of 50 are at an even higher risk, especially if they have a family history of the cancer. Excessive alcohol use and taking hormone-replacement drugs places women at a higher risk of developing breast cancer. Obese women and those who have never had children also tend to develop the disease more often.
Features
A severe form of acne called hidradenitis suppurativa causes blackheads and lesions -- or swollen red bumps -- to form on body parts where oil builds up in the sweat glands, such as those in the armpits. The bumps can become very large and tender, and drain pus when they break. Hidradenitis suppurativa usually begins around puberty and can worsen over time. Left untreated, the bumps can leave scars. Women and those with a family history of the skin condition are at highest risk.
Effects
A chronic skin condition called inverse psoriasis can cause bumps under the arm and become very painful. According to the American Academy of Dermatology, psoriasis is caused by an immune disorder that disrupts the skin's natural tendencies to shed dead skin cells. Instead, the cells pile up under the skin and form lumps. Various triggers can set off an outbreak of psoriasis and can include stress, cold weather or strep throat. A cut or scratch can precipitate an underarm outbreak within 10 to 14 days of the injury.
