Infections are the most common cause of swollen lymph nodes, and the vast majority of cases are nothing serious. Among people who visit a primary care doctor for unexplained swollen lymph nodes, only about 1.1 percent turn out to have a malignancy. That said, understanding the full range of causes, and knowing which features deserve attention, can help you make sense of what your body is telling you.
Lymph nodes are small, bean-shaped structures scattered throughout your body that filter fluid and trap bacteria, viruses, and other invaders. When they’re working hard to fight something off, they swell. You have clusters of them in your neck, under your jaw, behind your ears, in your armpits, and in your groin.
Infections: The Most Common Cause
A viral infection like the common cold is the single most frequent reason lymph nodes swell. Your body ramps up its immune response, and the nodes nearest to the infection fill with white blood cells. This is why a sore throat often comes with tender, swollen glands in your neck, and an ear infection can cause swelling behind the ear or along the jaw.
Common infections that trigger swollen nodes include:
- Upper respiratory infections (colds, flu)
- Strep throat
- Ear infections
- Abscessed teeth
- Skin or wound infections like cellulitis
- Mononucleosis (“mono”)
- Measles
With these, the swelling is typically localized. You’ll feel one or a few tender nodes near the site of infection, and they’ll go down as the illness resolves.
Less common infections can also be responsible. Tuberculosis, syphilis, and HIV all cause lymph node swelling. Cat scratch fever, a bacterial infection you can pick up from a cat scratch or bite, often produces a noticeably swollen node near the wound. Toxoplasmosis, a parasitic infection linked to undercooked meat or contact with infected cat feces, is another less frequent but real cause.
When Swelling Spreads to Multiple Areas
Sometimes nodes swell in several parts of your body at once rather than just one area. This generalized pattern points to infections or conditions that affect your whole system. Mononucleosis and HIV are two infections that commonly cause widespread swelling. Autoimmune conditions, where your immune system mistakenly attacks your own tissues, can do the same thing. Lupus and rheumatoid arthritis both involve chronic immune activation that can keep lymph nodes persistently enlarged.
Generalized swelling tends to be more clinically significant than a single tender node in your neck during cold season. If you notice swollen nodes in two or more separate areas of your body, that pattern is worth bringing up with a doctor.
Location Matters More Than You’d Think
Where a lymph node swells tells a lot about what’s causing it. Nodes in different parts of the body drain different regions, so the location often points directly to the source of the problem.
Swollen nodes in the groin are extremely common and rarely significant. These small, firm nodes (sometimes called “shotty” nodes) are often just a sign that your body has dealt with minor infections or irritation in the legs or genital area over time. In both the groin and armpit, a node generally isn’t considered concerning unless it reaches about 3 centimeters, roughly the size of a grape.
The supraclavicular area, the hollow just above your collarbone, is a different story. A node larger than 1 centimeter in this spot is considered significant because it often signals a deeper process in the chest or abdomen. A swollen node above the left collarbone has historically been associated with abdominal cancers, while one above the right collarbone more often points to something in the chest. Supraclavicular swelling in people over 40 carries a particularly high risk of malignancy, estimated at around 90 percent in one study. Even in younger adults, the risk is about 25 percent. This is the one location where swelling should prompt quick evaluation.
Cancer as a Cause
Cancers can cause lymph node swelling in two ways: cancer that starts in the lymph system itself (like lymphoma) or cancer that has spread to the nodes from somewhere else.
In Hodgkin’s and non-Hodgkin’s lymphoma, the affected nodes tend to be round, firm, and painless. They often grow steadily rather than appearing and resolving with an illness. On imaging, lymphoma nodes typically look uniformly solid and lack the normal fatty center that healthy nodes have.
When cancer from another organ spreads to a lymph node, the node may feel hard and fixed in place rather than freely movable under the skin. Painlessness is a common feature. Nodes that feel rubbery or rock-hard, don’t move when you push on them, and have been growing for weeks without an obvious infection deserve attention.
Still, it’s worth repeating: fewer than 2 out of every 100 people who show up at a primary care office with unexplained swollen lymph nodes turn out to have cancer. The odds are heavily in favor of a benign cause.
Medications That Cause Swelling
Certain drugs can trigger lymph node swelling as a side effect. Phenytoin, an anti-seizure medication, is one of the best-known culprits. Some medications used to prevent malaria can also cause it. In rarer cases, drugs that suppress the immune system, including methotrexate and a class of medications called TNF inhibitors (used for autoimmune conditions), have been linked to abnormal lymph node growth.
A separate reaction called drug hypersensitivity syndrome can cause widespread node swelling along with fever and rash. This is an immune overreaction to a medication, and it involves a surge of inflammatory signaling throughout the body. If swollen nodes appear shortly after starting a new medication, the timing is worth noting.
How to Tell Benign From Concerning
A few characteristics help distinguish routine swelling from something that needs further evaluation:
- Pain and tenderness are generally reassuring. Nodes that hurt when you press on them are usually fighting an infection. Painless nodes that keep growing are more worrisome.
- Mobility matters. A node you can easily slide under your fingertip is more likely benign. One that feels stuck to the tissue around it raises more concern.
- Texture gives clues. Soft or slightly firm nodes are typical of infection. Hard, rubbery, or matted-together nodes (where several feel fused into one mass) are less common and more likely to need investigation.
- Duration is key. Infection-related swelling typically peaks within a week or two and gradually resolves. Nodes that persist beyond three to four weeks, or continue growing, generally warrant a closer look.
What Happens During Evaluation
If a swollen node raises questions, the first step is usually a physical exam and medical history. Your doctor will check the node’s size, texture, and mobility, and look for obvious sources of infection nearby.
Blood tests can help identify infections or immune system problems driving the swelling. If the node is suspicious, ultrasound is a common next step. On ultrasound, healthy nodes look oval with a bright fatty center. Concerning features include a round shape, loss of that central brightness, irregular blood flow patterns, or signs of tissue breakdown inside the node.
A biopsy, where a small sample of tissue is removed and examined, is the definitive way to determine what’s going on inside a node. Doctors generally prefer to biopsy nodes in the neck or supraclavicular area rather than the groin or armpit, since nodes in those lower areas frequently show nonspecific inflammation that doesn’t give a clear answer.
For most people, swollen lymph nodes are a visible sign that the immune system is doing its job. They appear during a cold, an infection, or a minor injury, and they shrink back down once the threat passes. The small subset that lasts longer, grows steadily, or shows up in high-risk locations like the supraclavicular area is where the real diagnostic work begins.