Swollen Lymph Nodes: Causes and When to Worry

What lymph nodes do

You have around 600 lymph nodes. They sit along lymph vessels and filter fluid draining from nearby tissue. Inside them, white blood cells called lymphocytes recognize germs and multiply to fight them. That multiplication is what makes a node swell.

Normal nodes are usually less than half an inch (1 cm) across and often cannot be felt. Some are easy to feel in healthy people, especially in slim people and children: small nodes in the neck, under the jaw and in the groin are common and normal.

Because each group of nodes drains a specific area, the location of a swollen node is the best clue to the cause.

Swollen lymph nodes by location

A swollen node in the left supraclavicular area (sometimes called Virchow's node) can be a sign of cancer in the stomach or abdomen, so it always deserves prompt review.

Common causes of swollen lymph nodes

Infections (most cases)

• Upper respiratory infections: colds, flu and viral sore throats cause small, tender neck nodes that shrink as you recover.
• Strep throat and tonsillitis: larger, tender nodes under the jaw with a very sore throat and fever.
• Infectious mononucleosis (mono, glandular fever): often large nodes at the back and sides of the neck, severe sore throat, fever and tiredness lasting weeks. Common in teenagers and young adults.
• Dental infections: a tender node under the jaw on the same side as a painful tooth.
• Skin infections: cellulitis, infected cuts, insect bites or eczema flare-ups cause nodes in the region that drains them.
• Sexually transmitted infections: herpes, syphilis and others can swell groin nodes.
• Cat-scratch disease: a tender node in the armpit or neck a week or two after a cat scratch.

Reactive swelling after a vaccine

COVID-19, flu and other vaccines can swell armpit nodes on the side of the injection for a few weeks. If you are due a mammogram, tell the radiographer about recent vaccines.

Infected nodes (lymphadenitis)

Sometimes the node itself becomes infected. It turns red, hot, very painful and may fill with pus. This is lymphadenitis and needs antibiotics, and sometimes drainage.

Serious causes

These are uncommon, but they are why some swollen nodes need investigation.

• Lymphoma: usually painless, rubbery, gradually enlarging nodes, sometimes with night sweats, fevers, itching and weight loss.
• Leukemia: generalized node swelling with tiredness, paleness, bruising, bleeding and repeated infections.
• Cancer spread from elsewhere: hard, fixed nodes. Neck nodes can come from head and neck cancers (especially in smokers and drinkers), armpit nodes from breast cancer, and groin nodes from skin, genital or anal cancers.
• Tuberculosis: slowly enlarging, often painless neck nodes, sometimes with cough, fever and sweats.
• HIV: generalized swelling, sometimes as part of a flu-like illness early in infection.
• Autoimmune and inflammatory diseases: lupus, rheumatoid arthritis and sarcoidosis.
• Medicines: some anti-seizure medicines, such as phenytoin, can cause node enlargement.

When to worry about swollen lymph nodes

Most swollen glands are reactive and harmless. Features that make a serious cause more likely:

Tenderness usually means inflammation, which is reassuring. But a painless node is not automatically cancer, and a painful node is not automatically safe. The pattern over time matters most.

How doctors assess swollen lymph nodes

Your doctor will ask how long the swelling has been there, whether it has changed, about recent infections, cuts, scratches, travel, sexual history, pets, medicines and symptoms such as fever, night sweats, itching and weight loss. They will examine all node areas, the throat, skin, breasts or testicles as relevant, and feel for an enlarged liver or spleen.

If there is a clear infection, the usual plan is to treat it and recheck in 2 to 4 weeks. If the cause is unclear or the node has worrying features, tests may include:

• Blood tests: full blood count, inflammation markers, a mono test, and sometimes HIV, syphilis or toxoplasmosis tests
• Throat swab if strep is suspected
• Ultrasound: shows a node's size, shape and internal structure. Normal nodes are oval with a fatty center
• Chest X-ray or CT scan for nodes in several areas or above the collarbone
• Biopsy: a needle sample or surgical removal of the node, which gives a definite answer

Antibiotics "just in case" are not recommended without signs of bacterial infection, because they can delay the diagnosis.

Treatment and home care

Treatment depends on the cause. Reactive nodes from viral infections need no treatment and shrink on their own. While they do:

• rest and drink fluids
• use acetaminophen (paracetamol) or ibuprofen for pain or fever, following the label dose. Do not give aspirin to children or teenagers
• apply a warm compress to tender nodes for 10 to 15 minutes a few times a day
• treat the source: see a dentist for tooth pain, keep skin wounds clean

Bacterial infections such as strep throat or lymphadenitis need antibiotics. An abscess may need draining. Cancers and autoimmune diseases are treated by specialists.

A node can take several weeks to shrink completely, and some stay slightly enlarged but small and soft for good after a bad infection. That is normal.

Frequently asked questions

When should I worry about swollen lymph nodes?

See a doctor if a node is hard, fixed or painless and growing, is larger than about 1 inch (2.5 cm), lasts more than 4 to 6 weeks, appears above the collarbone, or comes with night sweats, fever or unexplained weight loss. Get urgent help for swelling that affects breathing or swallowing.

How long do swollen lymph nodes last?

After a common infection, they usually shrink within 2 to 4 weeks, sometimes up to 6 weeks. Mono can keep nodes enlarged for longer. A node that has not started to shrink after 4 weeks, or keeps growing, should be checked.

Are swollen lymph nodes a sign of cancer?

Rarely. The vast majority are caused by infection. Cancer is more likely when nodes are hard, painless, fixed, steadily enlarging, above the collarbone, or accompanied by night sweats, fevers or weight loss, and in people over 40. A doctor can assess this with an examination and, if needed, ultrasound or a biopsy.

Can stress cause swollen lymph nodes?

Stress does not directly cause swollen nodes. It can make you more prone to infections such as colds that do. If you have swollen nodes with no infection and they persist, see a doctor rather than putting them down to stress.

Why is only one side of my neck swollen?

One-sided swelling usually reflects an infection on that side, such as a tooth abscess, tonsillitis or an ear or skin infection. If there is no obvious cause and the node persists beyond a few weeks, have it examined.

Should swollen lymph nodes hurt?

Often they do. Pain and tenderness mean the node is swelling quickly because of inflammation, which is typical of infection. Painless nodes are common too, and are more of a concern only if they are large, hard, fixed or keep growing.