Lymph node
Lymph nodes are small, bean-shaped organs located at intervals along lymphatic vessels. They filter the lymph passing through them, detect bacteria and foreign material, and initiate immune responses. A lump you can feel on the side of your neck when you have a cold is also a sign that your lymph nodes are at work. Many people look them up because they are worried about a lump they can feel in their neck or armpit.
Where are they, and what do they do?
Hundreds of lymph nodes are distributed throughout the body. They cluster where several lymphatic vessels converge, such as the neck, under the jaw, the armpits, and the groin, where you may be able to feel them. There are also many inside the chest and abdomen. They are usually around 1 centimeter in size or smaller, so most cannot normally be felt.
They are shaped like kidney beans, with several lymphatic vessels (afferent lymphatic vessels) entering on one side. A smaller number of vessels (efferent lymphatic vessels) exit on the opposite side. As lymph enters and slowly passes through the internal mesh-like structure, macrophages and lymphocytes encounter and deal with foreign material, such as bacteria and damaged cells, and initiate immune responses. Because lymph is filtered as it passes through, lymph nodes are much like checkpoints along a road.
Lymph nodes carry out immune surveillance along the pathways through which lymph flows. For an overview of lymph flow, see Lymphatic circulation.
How you might notice them in everyday life
The most common experience is feeling swelling in the neck or under the jaw when you have a cold, a sore throat, or inflammation around a tooth. At these times, lymph nodes are increasing their immune cell numbers to fight invading bacteria or viruses, so they often become enlarged and slightly painful. As the body recovers, they usually return to their original size over a few days to a few weeks. An injury to an arm or leg may also cause lymph nodes in the armpit or groin on that side to swell.
Lymph nodes are located where lymph from the surrounding region collects. For example, lymph from the head and face flows to the lymph nodes in the neck, lymph from the arms and chest flows to those in the armpits, and lymph from the legs flows to those in the groin. Noticing which area is swollen can therefore help you get an idea of where inflammation may be present.
How to check them
If you can feel a lump, the following can help you check it.
- Gently feel it with the pads of your fingertips, using a circular motion. You do not need to press hard.
- Make a note of its size, how firm it is, whether it hurts, and whether it moves.
- Compare the two sides.
- Watch how it changes over a few weeks. Repeatedly touching it may temporarily make it larger, so check it only about once a day.
Treatments involving lymph nodes
During cancer surgery, the first lymph node to receive lymph from the affected area (the sentinel lymph node) may be examined or removed to check whether the cancer has spread. Removing lymph nodes can reduce lymph flow in that region and lead to lymphedema, which causes swelling in the arms or legs. This makes arm and leg care important after surgery.
When to take a closer look
Most swollen lymph nodes are a temporary response to infection. However, the cause needs further investigation in the following situations.
- A firm, painless lump keeps growing.
- A lump stays the same or gradually grows for more than 4 weeks without a reason such as a cold.
- There is also fever, drenching night sweats, or unexplained weight loss.
- A lump appears somewhere lymph nodes are not usually felt, such as above the collarbone.
- Lumps can be felt in several places at the same time.