What Is a Lymph Node, Where Are Lymph Nodes Located, and Why Do They Swell?

A lymph node, also called a lymph gland or lymphatic node, is a small, bean-shaped gland and a critical part of our body's immune system. These glands are scattered throughout a network of lymphatic vessels and serve as filters in the body's defenses. Lymph nodes contain white blood cells called lymphocytes that fight infectious agents and abnormal cells. In a healthy person, lymph glands are usually the size of a lentil or pea (a few millimeters in diameter), but they may swell and become palpable when activated by an infection or another condition. So what exactly is the lymphatic system, where are lymph nodes located in the body, why do they swell, and when is this concerning? In this article, you will find answers to these questions in light of scientific data.

What Is the Lymphatic System? Its Functions and Importance

The lymphatic system is a collection of organs and tissues that forms part of our immune system and creates a widespread network throughout the body, like blood vessels. The lymphatic system consists of lymph vessels carrying lymph fluid collected from tissues, lymph nodes that filter this fluid, and organs housing immune cells. Recovering excess fluid that leaks from the capillaries of the blood circulation and maintaining the body's fluid balance are among the lymphatic system's main functions. Without this system, fluid would accumulate and cause tissue swelling (edema). Lymph fluid is a colorless fluid containing white blood cells (lymphocytes), proteins, cellular debris, and some microbes.

The lymphatic system also plays a role in immune defense. Lymph fluid collected from tissues by lymph vessels is filtered as it passes through lymph nodes along the way. During this filtration, harmful microorganisms and abnormal cells are captured and destroyed by immune cells in the lymph nodes. This prevents these harmful elements from spreading into the bloodstream. The main organs of the lymphatic system include lymph nodes, the spleen, the thymus gland, the tonsils, and lymphoid tissues in the bone marrow. These organs are responsible for producing, maturing, and storing lymphocytes, forming the body's protective response to infections and diseases.

What Is a Lymph Node, and Where Is It Located?

A lymph node is a small, bean-shaped gland where immune cells gather. It has a capsule on the outside, compartments (lobules) containing lymphocytes inside, and sinuses between the lobules through which lymph fluid flows. Thin lymph vessels (afferent vessels) bring lymph fluid into the node; the filtered fluid returns to the circulation through outgoing lymph vessels (efferent vessels). Lymph nodes are normally about the size of a pea or <1 cm in diameter (an average of 12 mm in an adult). In total, there are approximately 500-600 lymph nodes in different regions of the body. Most are concentrated in the head and neck, armpits, chest, abdomen, and groin. For example, neck lymph glands filter lymph fluid from the head and throat; those in the armpits filter lymph from the arms and breasts, and those in the groin filter lymph from the legs and genital area. Lymph nodes are found in the neck, under the jaw, above the collarbone, armpit (axilla), chest cavity, abdomen, and groin (inguinal region), as well as almost everywhere else in the body, particularly where major vessels meet. Some lymph glands are deep within the body (for example, in the mediastinum between the lungs or around the intestines) and cannot normally be felt by hand; those near the surface (such as in the neck, armpits, or groin) may be felt as a small lump under the skin when enlarged.

Because lymph nodes trap and destroy harmful agents as part of the body's defenses, they become active and may enlarge during any infection or inflammatory condition. For example, swollen neck lymph glands during a throat infection are a sign of this defense mechanism. Normally small and mobile, lymph nodes can become a swollen lymph node (medically termed lymphadenopathy) during illness. These swellings may sometimes be painful, or they may simply be noticed as a painless mass.

Figure: Schematic view of the lymphatic system and the main lymph node regions. Bean-shaped lymph nodes (small brown structures) are distributed throughout the body along lymph vessels (brown lines).

The size and palpability of lymph nodes vary by region. For example, neck lymph glands in healthy people are generally <1 cm, whereas nodes up to ~1-1.5 cm in the groin may be considered normal. However, a lymph node larger than ~1.5 cm in the neck or ~2 cm in the groin is considered abnormally enlarged and requires investigation of the underlying cause. Palpable nodes in the supraclavicular region (above the collarbone) are particularly important because they may signal a more serious condition.

Why Do Lymph Nodes Swell? The Most Common Causes

Swollen lymph nodes act like a warning mechanism indicating that something in our body is not right. Infections are the most common cause of swollen lymph nodes. When the body fights an infection, lymph glands in the relevant region may enlarge and become tender as they produce and accumulate more immune cells. Swelling confined to one region (localized lymphadenopathy) is usually due to a local infection associated with that area. For example, neck lymph glands may swell with a throat infection, and glands under the jaw may swell with a dental abscess. If lymph nodes in several regions swell at the same time (generalized lymphadenopathy), this may be due to a more widespread infection affecting the whole body or a systemic disease.

The most common causes of swollen lymph nodes include:

• Common infections: Common colds, upper respiratory tract infections, rhinitis, strep throat (the beta bacterium), tonsillitis (inflammation of the tonsils), and sinusitis are common viral or bacterial infections that may particularly cause neck lymph glands to swell. Ear infections, dental infections (such as a dental abscess), and skin/wound infections are also common causes of regional lymph node enlargement. For example, a dental abscess may cause nodes under the jaw to swell, while a skin infection may affect nearby nodes. Lentil-like, "shotty" lymph glands in the neck are common during viral infections in children and are generally benign.

• Viral diseases: Mononucleosis (the "kissing disease" caused by the Epstein-Barr virus), measles, chickenpox, and similar viruses may cause widespread swelling of lymph nodes. For example, neck lymph glands become markedly enlarged in mononucleosis, an important sign of the disease. Similarly, HIV infection may also cause widespread lymph gland enlargement, particularly in its early stages.

• Less common infections: Tuberculosis (TB) can cause lymph node inflammation (lymphadenitis), leading to large, painless swellings, particularly in the neck. Syphilis and some other sexually transmitted diseases may cause the groin lymph glands to swell. Toxoplasmosis, a parasitic infection transmitted through infected cat feces or undercooked meat, may cause lymph gland enlargement. Cat-scratch disease (Bartonella bacteria) may also present with swollen lymph nodes, especially in the armpit or neck. Although these infections are less common in the community, they should be considered when lymph glands remain enlarged for a long time without an explanation.

• Immune system disorders: Lymph nodes can also enlarge in autoimmune diseases, in which the body attacks its own tissues. For example, in chronic inflammatory diseases such as systemic lupus erythematosus (SLE) or rheumatic diseases such as rheumatoid arthritis, there may be mild swelling of lymph glands, particularly in the neck, armpits, and groin. In these diseases, lymph gland swelling may become more prominent during flare-ups and is usually painless. Apart from autoimmune diseases, inflammatory conditions such as sarcoidosis may also lead to lymph node enlargement.

• Certain medications: Some drug treatments may cause swollen lymph glands, although this is rare. For example, phenytoin, a drug used to treat epilepsy, may trigger a hypersensitivity reaction in the body and lead to generalized lymphadenopathy. Temporary enlargement of lymph nodes in the relevant area may also occur after certain vaccinations (such as COVID-19 or BCG vaccines). Lymph gland swelling caused by drugs or vaccines generally resolves spontaneously after the drug is discontinued or some time passes.

Apart from the causes above, the issue that most worries people about swollen lymph nodes is the possibility of cancer. However, it is important to remember that most swollen lymph nodes are caused by infections or benign conditions and are unlikely to be due to cancer. Let us now take a closer look at the relationship between swollen lymph glands and cancer, as well as other signs of disease.

Are Swollen Lymph Nodes Associated with Cancer?

Although swollen lymph nodes are most often caused by conditions such as infection, some cancers can also enlarge lymph glands in rare cases. Cancer-related lymph node enlargement mainly occurs in two ways:

1. As a Sign of Lymphoma (Lymph Cancer): Lymphoma is a lymph node cancer that develops when immune cells called lymphocytes multiply uncontrollably. In other words, the cancer starts directly in the lymph node itself. Lymphomas are divided into two main groups: Hodgkin lymphoma and non-Hodgkin lymphoma. Hodgkin lymphoma is characterized on pathological examination by the presence of giant abnormal cells called Reed–Sternberg cells. These specific cells are not seen in non-Hodgkin lymphomas, and the cancer generally arises from B or T lymphocytes. Hodgkin lymphoma usually occurs in young adults and spreads in an orderly pattern through particular groups of lymph glands. Non-Hodgkin lymphoma is a broader group, can affect anyone from children to older adults, and may involve organs outside the lymphatic system. Lymphomas are known for causing painless, rubbery swellings in lymph nodes. Symptoms such as unexplained fever, night sweats, and weight loss often accompany them. Prolonged lymph node enlargement with no other explanation may therefore require investigation for lymphoma.

2. As a Result of Another Cancer Spreading (Metastasis): A cancer cell that develops anywhere in the body can break away from its organ of origin and reach lymph nodes through the lymphatic system. Like filters, lymph nodes attempt to capture these circulating cancer cells. Many escaped cancer cells are neutralized in the node, but some may settle and multiply there, forming a new tumor focus. This spread from the cancer's original site to the lymph glands is called lymph node metastasis. For example, breast cancer may first metastasize to the armpit lymph glands on the same side; oral or thyroid cancer may spread to neck lymph nodes. The spread of cancer cells to lymph nodes increases the disease stage and affects treatment planning. Therefore, when cancer is diagnosed, doctors examine the relevant nodes, assess them with imaging, and check them by biopsy if necessary. It is important to remember that lymph gland enlargement caused by cancer is relatively uncommon, and most cases of swollen lymph nodes have noncancerous causes.

Cancers other than lymphoma, such as blood cancers including leukemia, may also cause widespread enlargement of lymph glands. Leukemia is a cancer of blood and bone marrow cells, but particularly in certain types (such as ALL and CLL), cells also accumulate in lymph nodes and may cause swelling. Various organ cancers, such as breast, lung, stomach, and skin cancer (melanoma), may metastasize to nearby lymph nodes and make those glands palpable. For example, a palpable Virchow node above the left collarbone may be the first sign of cancer in the stomach or another abdominal organ. It is therefore important to consult a physician, particularly for unexplained, hard, persistent lymph node enlargement.

In summary, lymph node swelling alone is not an indicator of cancer. It is most often caused by benign conditions such as infection and returns to normal within a few weeks in such cases. However, lymph node enlargement may also be accompanied by other findings that vary with the cause. Let us now examine which diseases lymph gland swelling may indicate and when it should be considered serious.

What Diseases Can Enlarged Lymph Nodes Indicate?

As noted above, lymph nodes may swell for various reasons, including infections, immune diseases, or cancer. In this section, we will summarize possible diseases or conditions to consider when a swollen lymph gland is noticed. The table below lists causes of lymph gland enlargement by category, with examples of associated diseases:

Looking at the table above, we can see that the possible causes of swollen lymph glands cover a very broad range. Although infection is the most common cause, each category in the table may indicate a different disease. For example, a neck lymph gland may swell during an upper respiratory tract infection; chronic joint pain together with swollen neck and armpit nodes may suggest an autoimmune disease such as lupus or rheumatoid arthritis; and a skin wound infection may enlarge the node that drains that area.

What matters is to make an assessment together with the other findings accompanying lymph node swelling. Lymph gland enlargement alone may be caused by a simple infection or a serious disease; accompanying symptoms and the characteristics of the swelling help distinguish between them. Let us now consider when a swollen lymph node is regarded as dangerous and requires a visit to a doctor.

When Are Swollen Lymph Nodes Considered Dangerous?

We noted that lymph gland swelling is often harmless and temporary. For example, glands usually return to normal within a few weeks after a viral infection. In some circumstances, however, swollen lymph nodes may indicate a more serious problem. If the following signs or particular circumstances are present, swollen lymph nodes are considered dangerous or significant, and medical attention is needed:

• Persistent swelling: Lymph glands are generally expected to return to normal within 2-4 weeks after an infection. If a lymph node remains swollen for more than two weeks without an apparent infection, or does not shrink but instead continues to grow, this is significant. In particular, it must be evaluated if there is no improvement after 4 weeks. Lymph glands tend to shrink after ordinary infections resolve; if this does not happen, a different underlying problem may be present.

• A hard, immobile lymph node: Lymph glands swollen due to infection are normally elastic in consistency and mobile relative to surrounding tissues (they may slide under the skin). However, lymph nodes that feel hard, like stone, and are fixed to surrounding tissue (do not move) may suggest tumor-related growth. Cancer metastases or some lymphomas harden the structure of the node. Several nodes felt stuck together in a bundle (matted), particularly in tuberculous lymphadenitis, are also suspicious.

• Very large size: As noted above, nodes measuring >1.5-2 cm exceed the limits considered normal. A lymph node larger than a pea or bean, for example one reaching the size of a walnut, should be taken seriously, particularly in the absence of infection. Even a very small swelling in the supraclavicular region may be malignant at a rate of 25–90%, while swellings larger than 2 cm in regions such as the groin are noteworthy.

• Systemic symptoms accompanying swelling: Other warning signs in the body alongside lymph node enlargement are also a sign of danger. Unexplained fever (particularly persistent fever accompanied by night sweats), night sweats, weight loss, and loss of appetite may signal serious conditions, including lymphoma. For example, unintentional loss of more than 10% of body weight in 6 months is a typical finding in lymphoma patients. Other findings such as severe weakness, persistent fatigue, and unexplained skin rashes, an enlarged spleen or liver, and a persistent cough are also significant when seen alongside lymph node enlargement. If several of these symptoms occur together, the swelling should be investigated in detail rather than treated as a simple infection.

• Painless lymph gland swelling: Infection-related lymphadenopathy is generally tender and painful (inflammation causes pain). In contrast, painless lymph nodes that enlarge insidiously are more noteworthy. In particular, swellings that grow slowly over weeks or months without causing pain may occur in conditions such as tuberculous lymphadenitis or lymphoma. Although being painless does not necessarily mean something bad, it should suggest a noninfectious cause.

• Skin signs: If the skin over a swollen lymph node shows redness and increased warmth, this generally indicates inflammation of the lymph gland (lymphadenitis). A bacterial infection may be present, and antibiotics or drainage may sometimes be necessary. Nodes that enlarge as a deep, hard mass without skin discoloration should also draw attention.

In summary, the circumstances above are those in which lymph gland swellings exceed the usual limits and require evaluation by a physician. In such cases, your doctor will investigate the underlying cause through a detailed history and examination and, if necessary, further tests.

What Are the Symptoms of Swollen Lymph Nodes?

When your lymph nodes swell, various signs may alert you to this. In fact, lymph node swelling is itself a symptom and is generally accompanied by different findings depending on the underlying condition. Common signs of a swollen lymph node and symptoms that may accompany it can be summarized as follows:

• Palpable swelling: A swollen lymph node is noticed as a swelling or lump under the skin. Its size may range from a pea to a bean or even a walnut. For example, a gland swelling that you suddenly feel at the side of the neck or under the jaw may indicate this. The swelling may be felt at a single point or in several regions at once (such as both the neck and groin).

• Tenderness and pain: In infection-related lymph gland enlargement, tenderness or pain on touch in the affected region is common. For example, pressing swollen neck glands during a throat infection may cause pain. However, not all lymph node swellings have to be painful; some may enlarge without pain, particularly those that grow slowly.

• Redness and warmth of the skin: The skin over a swollen lymph node may sometimes be red and warm. This indicates active inflammation in that gland and is called lymphadenitis. For example, if you have a boil-like infection in your armpit, the lymph node in that area may swell and redden. Deep swollen nodes without skin changes are visible from outside only as a swelling.

• General signs of infection: If an infection is causing the lymph node swelling, symptoms of that infection will also occur. Fever, feeling cold, shivering, weakness, and other general signs of infection may accompany it. Particularly when associated with an upper respiratory tract infection, findings such as a runny nose, sore throat, and cough may occur. For example, if your neck nodes are swollen and you also have a runny nose and fever, it is probably due to a common cold.

• Findings of generalized lymphadenopathy: When lymph nodes in several regions swell (generalized lymphadenopathy), an underlying systemic condition may be responsible. In this case, swollen lymph glands throughout the body may be noticed. For example, palpable glands in the neck, armpits, and groin may indicate widespread infections such as mononucleosis or HIV, or a widespread immune disease such as lupus. Generalized lymphadenopathy is usually accompanied by systemic symptoms such as weakness, night sweats, and weight loss.

• Hardness or restricted mobility: The structure of a swollen node also provides clues. A soft, rubbery, mobile swelling is most often benign (for example, infection-related), whereas a very hard, rubber-like mass or one attached to surrounding tissues (immobile) may be more serious (such as tumor-related). Doctors assess the consistency and movement of a lymph node by hand to determine this.

• Other accompanying symptoms: Many different findings may accompany lymph gland swelling, depending on its cause. Examples include: Night sweats and prolonged fever (possibly signs of lymphoma), skin rashes or sores (such as a rash in toxoplasmosis or a skin fistula in tuberculous lymphadenitis), joint pain (in rheumatoid arthritis), abdominal pain or bloating (due to an enlarged spleen or liver). In a particular situation, pain in a swollen lymph node after drinking alcohol is a rare but specific sign of Hodgkin lymphoma. Thus, the symptoms of lymph node swelling can vary widely as a reflection of the underlying disease.

In brief, the most common sign of a swollen lymph node is a palpable swelling and tenderness in that area. However, other clues are needed to understand what caused it. At this point, healthcare professionals step in and use diagnostic methods to try to clarify the cause.

Medical Evaluation and Diagnostic Methods for Swollen Lymph Nodes

When you visit a doctor because of swollen lymph nodes, your doctor will first take a detailed medical history and perform a physical examination. At this stage, information such as when the swellings started, whether they are growing rapidly, whether they are painful, and other accompanying symptoms (fever, weight loss, and so on) is very valuable for diagnosis. Your doctor then examines the head and neck, armpits, groin, and other regions by hand to assess the lymph nodes' size, consistency, tenderness, and mobility. A comprehensive examination of lymph glands throughout the body is performed; an abdominal examination may also check for an enlarged spleen or liver (organomegaly).

Blood tests: After the initial assessment, certain laboratory tests are ordered to investigate possible causes. One of the most basic is a complete blood count (hemogram), which is checked for signs of infection (such as high white blood cell counts) or blood cancer (abnormal cells). Depending on the suspected condition, biochemistry tests (inflammatory markers, liver and kidney function, and so on) and specific infection screening (such as an EBV test for mononucleosis, toxoplasma antibodies, an HIV test, or a PPD skin test or Quantiferon blood test for tuberculosis) may be performed. In addition, if an autoimmune disease is suspected, rheumatology tests such as ANA and RF may be requested. These blood tests help narrow down the possible causes of swollen lymph nodes.

Imaging methods: Imaging methods are used to examine the internal structure of lymph glands and the condition of nodes deep within the body. Ultrasonography is a radiation-free method frequently used to assess lymph nodes in superficial regions (neck, armpits, groin). Ultrasound measures the node's size precisely and shows features such as whether its internal structure is homogeneous and its blood flow. If necessary, X-rays and particularly computed tomography (CT) or magnetic resonance imaging (MRI) and other advanced investigations are used to image nodes in regions such as the chest and abdomen. For example, a chest X-ray may investigate tuberculosis in prolonged neck lymphadenopathy, or a whole-body PET-CT scan may assess the extent of lymphoma. Imaging results help identify abnormal lymph glands and whether a biopsy is needed.

Lymph node biopsy: If a definitive diagnosis remains unavailable after the assessments above or your doctor has serious concerns, biopsy is the most reliable diagnostic method. A sample from the swollen lymph node is examined under a microscope. Biopsy usually involves surgically removing all or part of the node; sometimes a sample may be taken by needle biopsy (fine-needle aspiration or tru-cut). The pathologist examines the lymph gland tissue for cancer cells or, if an infection is present, its type (such as tuberculosis). Biopsy is particularly indispensable for diagnosing lymphoma, because the type and characteristics of lymphoma can only be determined through pathological examination. Similarly, if metastatic cancer is suspected, a lymph node biopsy may identify the cell type of the primary tumor. Biopsy results also guide treatment planning.

Other investigations: Additional tests may rarely be needed to determine why a lymph node has enlarged. Examples include culturing fluid from the node (particularly suppurative, or pus-filled, nodes) or using molecular tests such as PCR to look for tuberculosis or toxoplasma. In most cases, however, physical examination, blood tests, imaging, and biopsy are sufficient for diagnosis.

After the assessment, your doctor will identify the underlying cause of your lymph node swelling and recommend a treatment plan for it. So how is lymph node swelling treated? Let us address this in the final section.

How Is Lymph Node Swelling Treated? Treatment Options

Treatment for swollen lymph glands should be directed entirely at the underlying cause. There is no medication aimed solely at reducing the lymph node; once the cause is removed, the swelling usually subsides by itself. Different treatment approaches are therefore adopted depending on the cause identified during diagnosis:

• Infection-related lymph node swelling: Because infection is the most common cause, treatment is usually aimed at eliminating it. If bacterial infections are present, antibiotic treatment is the main approach. For example, if a bacterial dental abscess has caused a lymph node to swell, appropriate antibiotics and drainage treat it; in streptococcal throat infection, the neck glands also shrink when antibiotics are given. For viral infections, antibiotics are not beneficial. In this case, supportive care and time are the best solutions. Once the body defeats the virus, the lymph glands will also return to normal. For example, rest, plenty of fluids, and fever-reducing medication if needed are used for a common cold; the lymph glands also shrink within a few weeks. If an infected lymph node abscess has developed (filled with pus), a minor surgical procedure to empty it (drainage) followed by antibiotics may be necessary. For fungal or parasitic infections, antifungal or antiparasitic drugs are used. In special circumstances such as HIV infection, antiviral treatment for HIV (ART) may also bring lymph node swellings under control.

• Swelling due to immune system diseases: If the lymph node enlargement is caused by an autoimmune disease such as lupus or rheumatoid arthritis, the priority is to control these diseases. When the disease is suppressed using corticosteroids, immunosuppressive drugs, or biological agents prescribed by relevant specialists, reactive lymph gland swellings also decrease. For example, if treatment reduces joint inflammation in a patient with rheumatoid arthritis, the armpit lymph node will also shrink. Sarcoidosis and similar diseases may also show reduced lymph gland size with immune-regulating treatments (such as cortisone).

• In cancer (malignancy): If investigations determine that cancer is causing the lymph node swelling, treatment is planned according to that cancer's type and stage. If lymphoma is diagnosed, depending on its subtype (Hodgkin or non-Hodgkin) and extent, chemotherapy, immunotherapy, and/or radiotherapy may be required. High-dose chemotherapy followed by bone marrow (stem cell) transplantation is also a treatment option for some lymphomas. If leukemia is present, chemotherapy is the main treatment, and bone marrow transplantation may be used if needed. When solid organ cancers metastasize to lymph nodes, the primary tumor and affected nodes are generally removed through a surgical operation (such as axillary lymph node dissection in breast cancer). This is followed by radiotherapy or chemotherapy to try to eliminate remaining cells. Thus, treatment for cancer-related lymph node enlargement consists of treating the cancer itself with surgical and oncological therapies. Since a lymph gland may indicate the course of cancer, oncologists will continue to monitor the relevant nodes after treatment.

• Treatment for other causes: If a drug side effect has caused lymph node swelling, stopping that medication and switching to an alternative if needed resolves the problem (for example, starting another antiepileptic instead of phenytoin). After vaccination, lymphadenopathy usually resolves spontaneously within a few weeks; if very bothersome, painkillers or anti-inflammatory drugs may be used. For idiopathic lymphadenopathy (with no identified cause), the patient is monitored for a while; if it causes no symptoms and disappears over time, no intervention is needed.

• Supportive and symptomatic treatment: Alongside treatment of the cause, supportive measures may be taken to reduce the discomfort of swollen lymph nodes. Applying warmth (a warm compress) by placing a warm, damp cloth over the area may improve circulation and somewhat reduce pain and swelling. Applying a warm compress for 10-15 minutes several times a day is recommended. If there is pain or tenderness, over-the-counter painkillers or fever reducers such as paracetamol (acetaminophen) or ibuprofen may be taken. Drinking plenty of fluids and resting may support the body's resistance and speed recovery. Of course, these supportive treatments do not eliminate the underlying cause; however, they provide relief, particularly for infection-related swellings, and help the healing process.

In conclusion, treatment for lymph node swelling is not limited to a single drug or method; it is determined entirely by the cause of the swelling. What matters is distinguishing when these swellings are a normal bodily reaction and when they signal disease. Lymph gland swellings caused by infections are generally temporary and resolve after the infection improves. However, in uncertain cases, particularly when the features described above as "dangerous" are present, a healthcare facility must be consulted. With early diagnosis, treatment generally achieves successful outcomes, whether the cause is an infection or another disease. Our lymph nodes, the heroic sentries of our immune system, give us important signals about what is happening in our bodies; interpreting these signals correctly is critical for our health.