Swollen lymph nodes almost always mean your immune system is actively fighting something, usually an infection. These small, bean-shaped glands filter fluid and trap bacteria, viruses, and other threats. When they detect a problem, immune cells multiply rapidly inside them, causing the node to swell to several times its normal size within 48 to 96 hours. Most of the time, the swelling goes down on its own once the infection clears.
Why Lymph Nodes Swell
Lymph nodes are scattered throughout your body, clustered along pathways that drain fluid from nearby tissues. When bacteria or viruses reach a node, specialized immune cells called dendritic cells present the threat to other immune cells, triggering a cascade of activity. Within about two days, the node partially shuts down its normal outflow, increases blood flow, and recruits three to five times more immune cells than usual. The structural framework of the node stretches to accommodate all this new activity, and blood vessels inside the node grow to keep up.
This is why a swollen node often feels tender. The rapid expansion stretches the outer capsule of the node, creating that sore, pressure-like sensation you feel under your jaw during a cold or near your armpit after a cut on your hand gets infected. That tenderness is generally a reassuring sign. It means the node is reacting to something acute, not growing slowly and silently.
Common Causes by Location
Lymph nodes tend to swell closest to where the problem is. The location of your swollen node is one of the most useful clues to what’s causing it.
Neck (cervical nodes): These are the ones most people notice first. Upper respiratory infections, colds, sore throats, ear infections, and dental problems like gum disease or abscessed teeth are the most frequent triggers. Mononucleosis (“mono”) often causes prominent neck swelling on both sides.
Armpit (axillary nodes): Skin infections, cuts, or insect bites on the hand or arm commonly cause armpit node swelling. Vaccines can also trigger it. The Moderna COVID-19 vaccine caused armpit swelling or tenderness in about 16% of adults under 65 after their second dose. Vaccine-related swelling typically resolves within 60 days.
Groin (inguinal nodes): These nodes drain the legs, feet, and genital area. Swelling here can result from fungal infections like jock itch, sexually transmitted infections, urinary tract infections, cellulitis on the leg, or even an ingrown toenail or bug bite.
Causes Beyond Infection
While infections account for most swollen lymph nodes, other conditions can cause them too. Several autoimmune diseases trigger lymph node swelling as part of widespread immune activation, including lupus, rheumatoid arthritis, Sjögren syndrome, and sarcoidosis. In these cases, nodes often swell in multiple areas of the body at once rather than in just one spot.
Certain medications can also cause node swelling as a side effect. And as mentioned above, vaccines are a well-recognized trigger, particularly in the armpit nodes on the same side as the injection.
What Size Is Considered Abnormal
Healthy lymph nodes are usually less than 1 centimeter across (roughly the width of a pencil eraser) and you often can’t feel them at all. Nodes measuring more than 1 centimeter in their short-axis diameter are considered enlarged. In the abdomen, where nodes can only be seen on imaging, the upper limit of normal ranges from 6 to 10 millimeters depending on the specific location.
Size alone doesn’t tell the whole story, though. Shape matters too. Normal, healthy nodes tend to be oval, longer in one direction than the other. As nodes become infiltrated by something abnormal, they tend to become rounder. On imaging, a node whose length is less than twice its width raises more concern than a clearly oval node of the same size.
Signs That Suggest Something More Serious
The vast majority of swollen lymph nodes are harmless and temporary. But certain features raise the level of concern and warrant a closer look.
- Texture: Nodes that feel hard or rubbery, rather than soft and mobile, are more concerning. Benign, reactive nodes typically feel soft and slightly tender. Nodes that feel fixed in place, as if stuck to the tissue underneath, also warrant attention.
- Pain (or lack of it): Painless swelling that grows slowly over weeks is more worrisome than a tender node that appeared overnight. Tenderness usually signals an active immune response to infection.
- Location: Supraclavicular nodes, the ones just above your collarbone, carry the highest risk of being associated with cancer. In people over 40, as many as 90% of swollen supraclavicular nodes are linked to malignancy. Even in younger adults, the risk is around 25%. A swollen node above the left collarbone can signal a problem in the abdomen (such as stomach cancer), while one on the right side more often relates to the chest or lungs. Swollen supraclavicular nodes should always be evaluated, regardless of age.
- Number and spread: Swelling in multiple unrelated areas of the body (called generalized lymphadenopathy) is less likely to be a simple localized infection and may point to a systemic condition.
- Duration: Nodes that remain enlarged for more than two weeks without an obvious cause deserve medical evaluation. If unexplained swelling persists beyond one month, guidelines from the American Academy of Family Physicians recommend specific testing or biopsy.
Systemic Symptoms to Watch For
Swollen nodes combined with certain whole-body symptoms create a more urgent picture. Unexplained fevers above 38°C (100.4°F) lasting more than a month, drenching night sweats that soak your sheets, and unintentional weight loss of more than 10% of your body weight over six months are collectively known as “B symptoms” in the context of lymphoma. These symptoms aren’t exclusive to cancer (most infections can cause them too), but the combination of persistent, painless node swelling with one or more of these symptoms is a pattern that calls for prompt evaluation.
Rapidly enlarging nodes, especially with profound fatigue and these constitutional symptoms, tend to be associated with more aggressive forms of lymphoma. In contrast, slow, painless growth over months may suggest a lower-grade process.
How Swollen Nodes Are Evaluated
A physical exam is the starting point. Your doctor will feel the node’s size, shape, texture, mobility, and tenderness, all of which help narrow the possibilities. Blood work can check for signs of infection or immune activation.
If imaging is needed, ultrasound is often the first step. It can assess whether a node has a normal internal structure or shows concerning features like loss of its normal center, irregular borders, or an unusually round shape. CT scans provide a broader view, particularly for nodes deep in the chest or abdomen that can’t be felt on exam. On CT, nodes with a short-axis diameter of 15 millimeters or more are flagged for closer attention, while those under 10 millimeters are generally considered normal.
When a node looks suspicious on exam or imaging, a biopsy provides the definitive answer. Factors that push toward biopsy include age over 40, supraclavicular location, node diameter greater than about 2 centimeters, firm or hard texture, lack of tenderness, and an abnormal chest X-ray.
How Long Swelling Typically Lasts
Reactive swelling from a common infection usually peaks within a few days and resolves within two to three weeks as the infection clears. Some nodes, particularly in children, can remain slightly palpable for weeks after an illness without it meaning anything is wrong. Vaccine-related swelling follows a similar arc, with most cases resolving within two months, though rare cases have persisted longer.
If your nodes have been swollen for less than two weeks, you have an obvious infection like a cold or skin wound, the node is tender and movable, and you don’t have any of the systemic symptoms described above, the most likely explanation is that your immune system is simply doing its job.