The human body contains lymph nodes throughout, primarily in the head and neck, but also under the arms and in the groin. The lymphatic system consists of lymph nodes along with a number of organs and vessels.
Lymph nodes are small glands that comprise the lymph system, which in turn is part of the immune system. Each lymph node carries fluid, nutrients and waste between body tissues and the bloodstream. Lymph nodes also filter lymph fluid, catching viruses, bacteria and other foreign substances before destroying them using lymphocytes, which are specialized white blood cells.
When swollen, lymph nodes are typically the size of a pea, although they are sometimes even larger. Swollen lymph nodes are often a sign of infection, injury or cancer. It is typically easy to see swollen lymph nodes in the neck, under the arms and in the groin. In addition to visible swelling, signs of swollen lymph nodes include pain and tenderness.
In many cases, once the underlying condition is resolved, swollen lymph nodes return to normal size. If a lymph node remains swollen for more than two weeks, feels hard or doesn't move with the skin when pressed, it is a sign that a person should see a doctor.