Lymph Nodes

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Harmless and Concerning Findings

The approximately 500 lymph nodes in the human body are part of the lymphatic system, which also includes lymph vessels, the spleen, and the tonsils of the throat and palate. This system, which unlike the bloodstream is not a closed circuit, transports lymphatic fluid. This fluid forms when pressure from the blood forces liquid out of the blood capillaries into the space between cells, which is known as the interstitium. Muscle movement and breathing drive the fluid into the main lymphatic ducts, from where it enters the venous system.

Lymph nodes are found throughout the body; an adult has around 500 of them. If they lie close beneath the skin—such as in the neck, nape of the neck, armpits, and groin—they can be felt when they swell. Lymph nodes inside the body, near internal organs, cannot easily be felt when they swell.

Lymph nodes filter the two to three liters of lymphatic fluid produced daily, screening for harmful components such as viruses, bacteria, or cancer cells. They also ensure that lymphocytes mature and multiply. When lymphocytes recognize pathogens, they multiply significantly and the lymph node swells. B lymphocytes differentiate into plasma cells, which produce countless antibodies against the invader.

Lymph nodes usually swell because they are dealing with viruses. In such cases, they generally subside again within two to a maximum of four weeks. They may also enlarge briefly, for example under the armpit after a shaving injury, if there is a wound on the hand or arm, or after an insect bite.

If an infection persists — for example in the area of the teeth — or repeatedly returns, the immune response in the lymph nodes does not calm down. Autoimmune diseases such as lupus erythematosus, rheumatoid arthritis, or (rarely) Sjögren’s syndrome can also have a lasting effect on lymph nodes. Rarely, cancer may be the underlying cause.