Lymph nodes are found throughout the body. Causes of swollen lymph nodes include immune disorders and infection. Learn about treatment and much more. Not sick but noticing swollen lymph nodes? Learn when it’s a harmless immune response, red flag signs to watch for, how doctors evaluate it, and what actually matters. Swollen lymph nodes are normal and a sign that you are or were recently sick. If you have swollen lymph nodes but can’t find an obvious cause, talk to a healthcare provider. Lymph nodes are small, bean-shaped filters scattered throughout your body, and they swell when they trap bacteria, viruses, or other foreign material and ramp up their production of infection-fighting cells. Lymphadenopathy: Understand what are swollen lymph nodes, causes (infection, cancer), common symptoms, diagnosis & treatment. Your lymph nodes are vital filters in your immune system. Edward Chang, M.D., explains their location, function, what causes them to swell and their role in fighting infection and detecting cancer. Swollen lymph nodes most often happen because of infection from bacteria or viruses. Rarely, cancer causes swollen lymph nodes. The lymph nodes, also called lymph glands, play a vital role in the body being able to fight off infections.