The most common cause of swollen lymph nodes in the neck is a viral infection, such as a common cold, explains Mayo Clinic. Other causes of swollen lymph nodes include parasitic or bacterial infections, immune system disorders and cancer.
Common infections that may cause the lymph nodes to swell include measles, strep throat, ear infections, an abscessed tooth and mononucleosis, according to Mayo Clinic. Cellulitis or HIV may also cause swelling in the lymph nodes. Some uncommon infections, such as tuberculosis; sexually transmitted diseases, such as syphilis; toxoplasmosis, a parasitic infection; and cat-scratch fever, may also lead to swollen lymph nodes.
If a person has an immune system disorder, such as lupus or rheumatoid arthritis, swollen lymph nodes of the neck may occur, states Mayo Clinic. There are a number of cancers that also may cause lymph nodes to swell, including lymphoma and leukemia. It is also possible that cancer from another part of the body has spread to the lymph nodes. In some cases, medications such as phenytoin, an anti-seizure medication, may cause the lymph nodes to swell. Preventative medications for malaria can also cause this phenomenon.
Those who have swollen lymph nodes that do not go away in a few days should see a doctor, recommends Mayo Clinic. A visit to a family physician is usually the first step in finding out the cause.