Swollen lymph nodes are almost always a sign that your immune system is actively fighting something, most commonly an infection. You have roughly 600 lymph nodes throughout your body, and they act as filters that trap bacteria, viruses, and other threats. When they’re working hard, they swell, and you can feel them, usually in your neck, armpits, or groin. The vast majority of the time, they return to normal on their own within a few weeks.
The Most Common Causes
Infections are by far the leading reason for swollen lymph nodes. In children, short-lived viral illnesses like colds, flu, and upper respiratory infections are the most common trigger. In adults, the same holds true: a sore throat, sinus infection, ear infection, or skin wound near the swollen area is usually the explanation. Bacterial infections from staph or strep can cause neck nodes to swell rapidly and become quite tender.
Some less obvious infections also cause noticeable swelling. Mononucleosis (caused by Epstein-Barr virus) is a classic culprit, often producing swollen nodes in the neck that last for weeks. Toxoplasmosis, a parasitic infection picked up from undercooked meat, contaminated produce, or contact with cat feces, causes flu-like symptoms, muscle aches, and swollen nodes in otherwise healthy people. Cat-scratch disease, spread through a scratch or bite from an infected cat, can cause persistent swelling that lasts for months and is sometimes mistaken for something more serious.
Where the Swelling Is Matters
The location of your swollen nodes gives a strong clue about the cause, because each group of nodes drains a specific part of the body.
Neck: The most commonly noticed location. Usually tied to an upper respiratory infection, dental problem, or throat infection. Nodes that stay swollen for several months without an obvious infection can sometimes be caused by cat-scratch disease, sarcoidosis, or other chronic conditions. One location deserves special attention: nodes just above the collarbone (supraclavicular). Studies have found that 34% to 50% of people with supraclavicular swelling had a malignancy, with the highest risk in people over 40.
Armpits: Often caused by infections or injuries to the hand, arm, or chest wall. Cat-scratch disease is a common infectious trigger here. Swollen armpit nodes also appear after vaccinations given in the upper arm. When there’s no sign of infection or injury, armpit swelling raises more concern for lymphoma or cancers that have spread from the breast, lung, or skin. Silicone breast implants can also cause armpit node swelling from an inflammatory reaction to leaked silicone particles.
Groin: Healthy adults frequently have palpable groin nodes up to 2 cm across, so mild swelling here is often normal. When it’s not, the usual causes are sexually transmitted infections (herpes, syphilis, chlamydia) or skin infections on the legs or feet.
Near the elbow: Swollen nodes at the inner elbow are uncommon and are almost always considered abnormal when they’re larger than about 5 mm. This location is most associated with lymphoma or melanoma, though infections of the hand or forearm and syphilis can also be responsible.
Vaccines and Medications
If you’ve recently been vaccinated, that may be your answer. COVID-19 vaccines and boosters are well documented to cause swollen nodes in the armpit on the same side as the injection. Research published in the American Journal of Roentgenology found that this swelling takes an average of about 102 days to fully resolve after a booster dose. Imaging guidelines now recommend waiting at least 12 weeks before investigating vaccine-related node swelling further, and suggest not delaying routine mammograms in the meantime.
Certain medications can also trigger swollen nodes. Methotrexate, used for rheumatoid arthritis and psoriasis, can produce changes in lymph nodes ranging from benign swelling to more serious overgrowth of immune cells. TNF inhibitors, another class of drugs used for autoimmune conditions, have been linked to similar effects. If you started a new medication in the weeks before your nodes swelled, it’s worth flagging for your doctor.
Autoimmune Conditions
When lymph nodes swell in multiple areas at once (neck, armpits, and groin simultaneously, for example), the cause is more likely to be systemic rather than a local infection. Autoimmune diseases like lupus, rheumatoid arthritis, and sarcoidosis can all drive widespread node swelling. In these cases, you’ll typically have other symptoms too: joint pain, fatigue, skin rashes, or unexplained fevers. The swelling tends to wax and wane alongside disease flares rather than appearing suddenly and resolving in a couple of weeks like an infection would.
What Size and Texture Tell You
Not all swollen nodes are equal, and the physical characteristics matter. Nodes larger than 1 cm are generally considered enlarged. Those over 2 cm raise more concern for malignancy or a granulomatous process like tuberculosis or sarcoidosis.
Texture provides additional information. Soft, tender nodes that move easily under your fingers are typical of infections and inflammation. Firm, rubbery nodes that don’t hurt are more characteristic of lymphoma. Hard nodes that feel fixed in place and don’t move when you push on them suggest a solid tumor that has spread from elsewhere. A node that grows steadily over weeks without any signs of infection is more concerning than one that appeared overnight alongside a sore throat.
How Long Swelling Should Last
Most infection-related swelling peaks within a few days and resolves within two to three weeks as the infection clears. Some infections, particularly cat-scratch disease and mononucleosis, can keep nodes swollen for several months.
The general clinical guideline is that unexplained swollen nodes deserve closer attention if they persist beyond three to four weeks. At that point, if there’s no clear explanation, your doctor may recommend imaging (usually ultrasound or CT) to get a better look at the node’s size and structure. A biopsy, where a small sample of tissue is removed for examination, is typically the next step if the node keeps growing, is in a high-risk location like above the collarbone, or is accompanied by unexplained weight loss, night sweats, or persistent fevers.
Signs That Need Prompt Attention
Most swollen lymph nodes are harmless and temporary. But certain combinations of features warrant a quicker evaluation:
- Location above the collarbone on either side, at any age
- Nodes larger than 2 cm that are hard, painless, or fixed in place
- Swelling in multiple unrelated areas without an obvious infection
- Accompanying symptoms like unexplained weight loss, drenching night sweats, or fevers lasting more than two weeks
- Steady growth over weeks without tenderness or other signs of infection
In children, swollen neck nodes are extremely common and are overwhelmingly caused by viral infections. Pediatric lymph nodes also tend to run larger than adult nodes at baseline. Studies of healthy children found that submandibular neck nodes averaged nearly 2 cm in length, which would be considered borderline in an adult. So a palpable node in a child’s neck during cold season is rarely cause for alarm on its own.