Swollen lymph nodes under the arm may swell due to injury or infection in the hand or arm, explains WebMD. Other causes for swelling in this area are lymphoma or breast cancer though this is rare.
The treatment for swollen lymph glands depends on the cause, according to WebMD. For instance, if the swelling is due to a bacterial infection, the swelling is treated with antibiotics. If the swelling is caused by a virus, it goes away on its own, but if cancer is suspected, a biopsy may be done. A person should see a doctor if the lymph node swelling does not go away within a month.
In some cases, the lymph nodes may swell in another area in addition to under the arms, claims WebMD. In this situation, the swelling may be due to a viral illness, mononucleosis, strep throat or as a side effect of medication. Other causes for this type of swelling include a side effect of the measles-mumps-rubella vaccine, syphilis or HIV. Lyme disease may cause swelling in more than one areas, too.
Individuals should be aware that lymph nodes may remain swollen for several weeks, even after the cause is gone, states WebMD. This is more common in children, who may have firm, swollen lymph nodes for many weeks following treatment.