What Are Lymph Nodes?

Lymph nodes are your immune system’s first line of defense, protecting you from things like bacteria or viruses that could make you sick.

You have hundreds of the small, round, or bean-shaped glands all over your body. Most are spread out, but some are found in groups in a few major places, like your neck, under your arm, and in your chest, belly, and groin. You might be able to feel some of the clusters in those areas as little bumps, but typically, you don’t feel them or even know they are three.

Your lymph nodes are part of your lymphatic system. Along with your spleen, tonsils, and adenoids, they help you fight off illness and infections.

How Do They Work?

Your lymph nodes are connected to one another by lymph vessels (tubes that run through your body like veins). They carry lymph fluid — a clear, watery liquid that passes through the nodes.

As the fluid flows through, cells called lymphocytes help protect you from harmful germs.

There are two kinds of lymphocytes — B-lymphocytes (or B-cells) and T-lymphocytes (or T-cells).

• B-cells make antibodies that attach to germs and let your immune system know they need to be killed off.
• T-cells have a couple of jobs. Some destroy germs, while others keep track of immune cells. They let your body know when to make more of certain kinds and less of others. Memory T cells are T-cells that remain dormant after an infection and become active again when they are faced with the same infection.

Lymph fluid also carries protein, waste, cellular debris (what’s left after a cell dies), bacteria, viruses, and excess fat that are filtered by the lymphatic system before it’s dumped back into the bloodstream.

Swollen Lymph Nodes

When there’s a problem in your body, like an illness or an infection, your lymph nodes can swell. (This usually happens only in one area at a time.) It’s a sign that more lymphocytes are in action than usual, trying to kill off germs.

You may notice this most often in the glands in your neck. That’s why your doctor feels the area under your jawbone. They’re checking to see if those glands are bigger than usual or tender.

Many things can make your lymph nodes swell. Any infection can trigger it, including a cold or the flu, an ear infection, STDs (usually inguinal), shingles, tuberculosis, or an abscessed tooth. Rarely a vaccine can cause swollen lymph nodes on the side of the vaccination. Much less often, it can be a sign of something more serious, like cancer.

Sometimes medicines like phenytoin (taken for seizures), or drugs that prevent malaria can cause swollen lymph nodes, too.

Show Sources

American Academy of Pediatrics: “Swollen Glands.”

American Cancer Society: “What is Hodgkin disease?”

Mayo Clinic: “Parts of the immune system,” “Swollen lymph nodes.”

The Merck Manual of Medical Information– Second Home Edition, Merck & Co., 2003

University of Rochester Medical Center: “Why the Healthcare Provider Examines the Neck and Throat.”