Swollen lymph nodes (adenitis) are usually caused by bacterial or viral infections. These include throat infections, measles, ear infections, gum and tooth disease (abscess), mononucleosis, skin or wound infections, HIV (the virus that causes AIDS). Less common causes include tuberculosis, sexually transmitted diseases such as syphilis, and diseases such as toxoplasmosis. Adenitis can rarely be caused by cancer. Swelling in the lymph nodes is a sign that the body is fighting an illness, and the lymph nodes will return to their normal size once the illness is resolved. Sometimes, medications or exposure to allergens can also cause lymph node enlargement.