Doctors seldom know why one person develops non-Hodgkin lymphoma and another does not. But research shows that certain risk factors increase the chance that a person will develop this disease.

In general, the risk factors for non-Hodgkin lymphoma include the following:

• Weakened immune system: The risk of developing lymphoma may be increased by having a weakened immune system (such as from an inherited condition or certain drugs used after an organ transplant).
  
  
• Certain infections:Having certain types of infections increases the risk of developing lymphoma. However, lymphoma is not contagious. You cannot catch lymphoma from another person.
  
  The following are the main types of infection that can increase the risk of lymphoma:
  • Human immunodeficiency virus (HIV): HIV is the virus that causes AIDS. People who have HIV infection are at much greater risk of some types of non-Hodgkin lymphoma.
  • Epstein-Barr virus (EBV): Infection with EBV has been linked to an increased risk of lymphoma. In Africa, EBV infection is linked to Burkitt lymphoma.
  • Helicobacter pylori: H. pylori are bacteria that can cause stomach ulcers. They also increase a person's risk of lymphoma in the stomach lining.
  • Human T-cell leukemia/lymphoma virus type 1 (HTLV-1): Infection with HTLV-1 increases a person's risk of lymphoma and leukemia.
  • Hepatitis C virus: Some studies have found an increased risk of lymphoma in people with hepatitis C virus. More research is needed to understand the role of hepatitis C virus.
    
    
• Age: Although non-Hodgkin lymphoma can occur in young people, the chance of developing this disease goes up with age. Most people with non-Hodgkin lymphoma are older than 60. (For information about this disease in children, call the NCI's Cancer Information Service at 1-800-4-CANCER.)
  

Researchers are studying obesity and other possible risk factors for non-Hodgkin lymphoma. People who work with herbicides or certain other chemicals may be at increased risk of this disease. Researchers are also looking at a possible link between using hair dyes before 1980 and non-Hodgkin lymphoma.

Having one or more risk factors does not mean that a person will develop non-Hodgkin lymphoma. Most people who have risk factors never develop cancer.

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