Causes

Lymph nodes are small, round or bean-shaped clusters of cells. Inside lymph nodes are a combination of different types of immune system cells. These specialized cells filter your lymphatic fluid as it travels through your body and protect you by destroying invaders.

Lymph nodes are located in groups, and each group drains a specific area of your body. You may be more likely to notice swelling in certain areas, such as in the lymph nodes in your neck, under your chin, in your armpits and in your groin. The site of the swollen lymph nodes may help identify the underlying cause.

The most common cause of swollen lymph nodes is an infection, particularly a viral infection, such as the common cold. Other possible causes of swollen lymph nodes include:

Common infections

• Strep throat
• Measles
• Ear infections
• Infected (abscessed) tooth
• Mononucleosis
• Skin or wound infections, such as cellulitis
• Human immunodeficiency virus (HIV) — the virus that causes AIDS

Uncommon infections

• Tuberculosis
• Certain sexually transmitted infections, such as syphilis
• Toxoplasmosis — a parasitic infection resulting from contact with the feces of an infected cat or eating undercooked meat
• Cat scratch fever — a bacterial infection from a cat scratch or bite

Immune system disorders

• Lupus — a chronic inflammatory disease that targets your joints, skin, kidneys, blood cells, heart and lungs
• Rheumatoid arthritis — a chronic inflammatory disease targeting the tissue that lines your joints (synovium)

Cancers

• Lymphoma — cancer that originates in your lymphatic system
• Leukemia — cancer of your body's blood-forming tissue, including your bone marrow and lymphatic system
• Other cancers that have spread (metastasized) to lymph nodes

Other possible but rare causes include certain medications, such as the anti-seizure medication phenytoin (Dilantin) and preventive medications for malaria.