Swollen lymph nodes in the neck are most often caused by a common cold, flu, or other upper respiratory infection. Lymph nodes are small, bean-shaped structures that filter fluid and trap bacteria, viruses, and other threats. When your body fights an infection in or near the head and neck, the closest lymph nodes ramp up their immune response and swell. The vast majority of cases are harmless and resolve on their own, but persistent or unusual swelling can sometimes signal something more serious.
How Lymph Nodes in the Neck Work
Your neck contains several clusters of lymph nodes arranged in a chain from just below your jaw down to your collarbone. Each group drains a specific area. The nodes under your jaw filter fluid from your mouth and lower face. The nodes along the side of your neck handle drainage from your throat, nasal passages, and voice box. Nodes near your collarbone drain from deeper structures like your thyroid and esophagus.
When an infection or inflammation occurs in any of these areas, the nearest lymph nodes fill with immune cells and begin filtering the threat. That’s what creates the swelling you can feel. The location of the swollen node often gives a clue about where the problem started: a sore throat tends to swell nodes along the side of your neck, while a dental infection swells the nodes under your jaw.
Viral Infections: The Most Common Cause
Viral upper respiratory infections cause the majority of swollen neck lymph nodes, especially in children. The common cold, flu, and adenovirus infections all trigger temporary swelling that usually resolves within a week or two as the illness clears. This type of swelling typically appears on both sides of the neck at once.
Some viruses cause more prolonged swelling. Epstein-Barr virus, which causes mono, and cytomegalovirus (CMV) can keep lymph nodes enlarged for weeks or even months. With mono, you may notice significant swelling in the neck along with extreme fatigue, sore throat, and fever. This kind of lingering swelling falls into the “subacute” or “chronic” category but is still benign.
Bacterial Infections and Dental Problems
Bacterial infections are the second most common trigger. Strep throat and staph skin infections on the face or scalp can both cause noticeable neck node swelling, often on one side. The nodes may feel tender and warm. Dental abscesses, infected gums, and ear infections are also frequent culprits, particularly for swelling under the jaw or behind the ear.
In some cases, the lymph node itself becomes infected, a condition called lymphadenitis. When this happens, the node can grow large and painful, and the overlying skin may turn red. If pus collects inside the node, it forms an abscess that feels rubbery or fluctuant. Untreated lymphadenitis can lead to abscess formation that may need to be drained.
Autoimmune and Inflammatory Conditions
Conditions where the immune system is chronically activated can cause persistent lymph node swelling. Lupus, rheumatoid arthritis, and sarcoidosis all involve ongoing inflammation that keeps lymph nodes enlarged, sometimes for months. The swelling in these cases tends to be milder and less tender than infection-related swelling, and it often appears in multiple areas of the body, not just the neck.
Medications and Vaccines
Certain medications can trigger lymph node swelling as a side effect. Methotrexate, commonly used for rheumatoid arthritis and psoriasis, can produce changes in lymph nodes ranging from mild reactive swelling to more significant enlargement. Sulfasalazine, an anti-inflammatory drug, occasionally causes a hypersensitivity reaction about three weeks after starting the medication, with fever, rash, joint pain, and swollen lymph nodes. Some vaccines, particularly those given in the upper arm, can cause temporary swelling in nearby nodes including the neck and armpit.
When Swelling May Signal Cancer
Cancer is a far less common cause of swollen neck nodes, but it’s usually the concern behind this search. Lymphomas (cancers of the lymphatic system) typically produce painless, rubbery nodes that may feel matted together. Cancers of the head and neck, such as throat or mouth cancer, can also spread to nearby lymph nodes. Cancers from other parts of the body occasionally metastasize to neck nodes as well.
Several features raise the level of concern. Risk factors for a malignant cause include being over 40, swelling that lasts longer than four to six weeks, and the presence of systemic symptoms: unexplained fevers, drenching night sweats, or weight loss greater than 10% of your body weight without trying. A node that feels hard, irregular, or fixed in place (it doesn’t move when you push it) is more suspicious than one that’s soft, smooth, and mobile.
Location matters too. Swollen nodes just above the collarbone (the supraclavicular area) are considered abnormal regardless of size and warrant prompt evaluation. Nodes in this spot can be associated with cancers of the lung, breast, or abdomen draining upward through the lymphatic system.
What the Node Feels Like Matters
The physical characteristics of a swollen lymph node tell you a lot. Nodes that are tender, soft, and move freely under your fingers are almost always reactive, meaning they’re responding to a nearby infection and will shrink back down. Nodes caused by infection are often under 1 centimeter and may be slightly warm.
Nodes larger than 2 centimeters in the neck, or any palpable node above the collarbone, deserve medical attention. A node that is hard, painless, irregularly shaped, or stuck to the tissue underneath it is more concerning. That said, physical characteristics alone aren’t reliable enough to rule cancer in or out, so imaging or a biopsy is sometimes needed for nodes that don’t fit the typical reactive pattern.
How Long Swelling Should Last
Most swollen lymph nodes from a viral infection shrink noticeably within two weeks. After a bacterial infection, they may take a bit longer, especially if you needed antibiotics. The general guideline is that a node should be trending back toward its normal size within four to six weeks. If a node hasn’t returned to baseline by eight to 12 weeks, further evaluation is typically recommended.
It’s worth noting that lymph nodes can remain slightly palpable (you can still feel them) long after an infection resolves. Small, mobile, non-tender nodes in the neck are a normal finding, particularly in children and thin adults. The concern isn’t that you can feel a node; it’s when one is new, growing, unusually large, or accompanied by other symptoms.
What to Watch For
A single swollen node during a cold is not a reason for alarm. But certain combinations of symptoms and features should prompt a medical visit sooner rather than later:
- Size over 2 centimeters or rapid growth over days to weeks
- No obvious infection to explain the swelling
- Systemic symptoms like persistent fevers, night sweats, unexplained weight loss, or unusual fatigue
- Node characteristics that feel hard, fixed, or painless
- Supraclavicular location, just above the collarbone on either side
- Duration beyond six weeks without improvement
- Easy bruising or bleeding alongside swollen nodes, which can point to blood cancers like leukemia
If your swollen lymph nodes check none of these boxes and you have an obvious explanation like a cold, sore throat, or recent dental work, the swelling will very likely resolve on its own as the underlying issue clears.