Why is only one lymph node swollen? Understanding localized lymphadenopathy

October 1, 2025 •

4 min read

Localized swelling affecting a single lymph node group is a common occurrence, and it most often indicates an issue in the immediate vicinity. While it can be alarming to find a single swollen lymph node, this is typically a normal immune response to a nearby infection, irritation, or injury.

Quick Summary

Localized lymphadenopathy, where only one lymph node is swollen, is a frequent immune reaction to a nearby infection or injury. The specific location of the swelling can often pinpoint the problem area. Less commonly, it could signal a more serious, but still localized, condition, or a rare case of cancer, which presents different symptoms. Evaluation of characteristics like size, movement, and tenderness helps distinguish benign from potentially malignant issues.

Key Points

Local Cause, Local Swelling: A single swollen lymph node most often signifies a localized infection, injury, or inflammation occurring in the area immediately surrounding that node.
Normal Immune Response: The swelling is a sign that your lymphatic system is actively filtering and fighting off germs, which is a normal function of a healthy immune system.
Benign vs. Malignant Characteristics: Benign swollen nodes are typically tender, soft, and movable, and they resolve in a few weeks, whereas potentially malignant nodes are often hard, painless, fixed, and persistent.
COVID-19 Vaccine Side Effect: Swelling in a single armpit lymph node can be a temporary and harmless side effect of the COVID-19 vaccine.
Consider the Location: The specific location of the swollen lymph node provides clues; for instance, a neck node points toward a throat or ear infection, while an armpit node suggests an issue in the arm or breast area.
When to See a Doctor: Seek medical advice if the swelling persists beyond two to four weeks, feels hard or fixed, or is accompanied by other worrying symptoms like unexplained weight loss or fever.

Understanding the lymphatic system and its function

Your lymphatic system is a critical part of your immune system, composed of a network of vessels and small, bean-shaped organs called lymph nodes. These nodes act as filters, trapping and destroying germs, viruses, and other foreign substances before they can spread further through the body. When your body detects an invader or injury in a specific area, the lymph nodes nearest to the site of the problem ramp up production of immune cells, causing them to swell. This is a normal, healthy response, and it is the primary reason why you might find only one lymph node swollen.

Common causes of a single swollen lymph node

When a lymph node swells in isolation, the cause is most often a localized, and typically harmless, issue. The location of the swollen node provides an important clue to the underlying problem.

Localized infections

Throat and ear infections: Infections in the throat (like strep throat or tonsillitis) or ear can cause the lymph nodes in the neck and under the jaw to swell. Swelling may occur on one side if the infection is primarily on that side.
Dental issues: An abscessed or impacted tooth, mouth sores, or inflamed gums (gingivitis) can lead to swollen lymph nodes under the chin and along the jawline.
Skin infections: A minor skin infection, insect bite, or a localized rash (such as poison ivy) on an arm or hand can cause swelling in the armpit lymph nodes. Similarly, an infection or injury on the foot or leg might affect the groin lymph nodes.
COVID-19 vaccination: Some COVID-19 vaccines have been known to cause temporary, localized lymph node swelling in the armpit on the injection side. This is a normal immune response and typically resolves within a few weeks.

Non-infectious causes

Injury: The lymphatic system also responds to physical trauma. A cut, scrape, or other injury near a lymph node group can trigger it to swell.
Inflammation: Localized inflammatory conditions or allergic reactions can cause swelling as the immune system is activated.

When a single swollen lymph node might be serious

While the vast majority of cases are benign, a single swollen lymph node can, in rare circumstances, indicate a more serious condition. It is the combination of specific characteristics that can help differentiate a simple immune response from a potential malignancy.

Cancer

Metastatic cancer: Cancer cells that break away from a primary tumor can travel through the lymphatic system and get trapped in a nearby lymph node, causing it to swell. For example, breast cancer can spread to the armpit lymph nodes.
Lymphoma: This is a cancer that begins in the lymphatic system itself, including the lymph nodes. Lymphoma can cause swelling in one or more lymph nodes.

Autoimmune disorders

Certain autoimmune diseases, where the immune system attacks healthy tissue, can also lead to lymph node swelling. However, these conditions more often cause widespread (generalized) swelling rather than affecting just a single node.

What to look for: Benign vs. potentially malignant lymph nodes

Distinguishing between a harmless and a more concerning swollen lymph node requires attention to several key features. A doctor will typically consider these characteristics during a physical examination.


Feature	Typically Benign Swollen Lymph Node	Potentially Malignant Swollen Lymph Node
Tenderness	Often painful or tender to the touch, especially in infectious cases.	Usually painless, particularly in the initial stages.
Mobility	Feels soft or spongy and moves easily under the skin when pressed.	Often feels hard, firm, or fixed in place, not moving freely.
Size	Small, often pea-sized (less than 1 cm), and fluctuates in size.	Grows larger over time, sometimes exceeding 1 cm, and does not shrink.
Duration	Resolves within a few weeks (typically 1–2) as the infection clears.	Persists for longer than a few weeks or months.
Associated Symptoms	Often accompanies other signs of infection, such as sore throat, fever, or rash.	Can occur without an apparent infection and may be accompanied by unexplained weight loss, night sweats, or fever.

When to see a doctor

While many swollen lymph nodes resolve on their own, certain signs warrant medical attention. Contact your healthcare provider if you observe any of the following:

The swollen lymph node persists for more than two weeks.
The node is hard, fixed, or irregular in shape.
The node continues to grow larger.
The swelling is located in an unusual area, such as above the collarbone.
The swelling is accompanied by persistent fever, night sweats, or unexplained weight loss.

A doctor will perform a physical exam and review your medical history to determine the cause. Depending on the findings, further tests such as blood tests, imaging (like an ultrasound), or a lymph node biopsy may be necessary for an accurate diagnosis.

Conclusion

Discovering a single swollen lymph node is a common experience that can often be attributed to a minor, local infection or injury, representing a normal and healthy immune response. The proximity of the swelling to the source of the problem is a key indicator of its localized nature. While less common, certain characteristics—such as a node that is hard, fixed, or persists for an extended period—may point to a more serious underlying issue. Paying attention to these differentiating features is important. Though most cases are benign and resolve on their own, seeking medical advice is prudent for any persistent, unexplained, or concerning swelling to ensure proper diagnosis and care. Based on information from the Cleveland Clinic, a localized swelling often just means the infection is nearby.

Frequently Asked Questions

Yes, but it is rare. A single swollen lymph node can, in rare cases, indicate a cancer that has spread to that node (metastatic cancer) or a cancer of the lymphatic system itself (lymphoma). However, the vast majority of solitary swollen lymph nodes are due to benign causes like infection.

A swollen lymph node is potentially serious if it feels hard, fixed, or immobile, persists for more than two to four weeks, continues to grow, or appears without any apparent infection. It is especially concerning if accompanied by unexplained weight loss, night sweats, or fever.

A swollen lymph node caused by a common infection typically lasts for one to two weeks, gradually returning to its normal size as the infection resolves. Some can take several weeks to return to normal, but should not continue to grow.

Yes, absolutely. A localized infection, such as an ear infection, a sore throat, or a dental abscess, can cause only the nearest lymph node or node group to swell as it works to fight off the invading germs.

The most common causes for swollen lymph nodes in the neck are upper respiratory infections, such as the common cold, strep throat, or ear infections. Dental infections can also cause localized swelling in this area.

Anxiety itself does not directly cause lymph nodes to swell. However, chronic stress and anxiety can weaken the immune system, making you more susceptible to infections that can then cause swollen glands.

Cancerous lymph nodes are often painless, especially in the early stages, though this is not a hard rule. Painful, tender lymph nodes are more commonly associated with an infection.