Researchers have found several factors that may affect a person's chance of getting non-Hodgkin lymphoma. There are many types of lymphoma, and some of these factors have been linked only to certain types.

Age

Getting older is a strong risk factor for this disease, with most cases occurring in people in their 60s or older.

Exposure to Certain Chemicals

Some studies have suggested that chemicals such as benzene and certain herbicides and insecticides (weed- and insect-killing substances) may be linked with an increased risk of non-Hodgkin lymphoma. Research to clarify these possible links is still in progress.

Some chemotherapy drugs used to treat other cancers can increase the risk of developing leukemia or non-Hodgkin lymphoma many years later. For example, patients who have been treated for Hodgkin disease have an increased risk of later developing non-Hodgkin lymphoma. But it's not totally clear if this is related to the disease itself or if it may be an effect of the treatment.

Radiation Exposure

Studies of survivors of atomic bombs and nuclear reactor accidents have shown they have an increased risk of developing several types of cancer, including leukemia, thyroid cancer, and non-Hodgkin lymphoma. Patients treated with radiation therapy for some other cancers, such as Hodgkin disease, have a slightly increased risk of developing non-Hodgkin lymphoma later in life. This risk is greater for patients treated with both radiation therapy and chemotherapy.

Immune System Deficiency

People with weakened immune systems are at increased risk for non-Hodgkin lymphoma. For example, patients who receive organ transplants (kidney, heart, liver) are treated with drugs that suppress their immune system to prevent it from attacking the new organ. These patients have an increased risk of developing non-Hodgkin lymphoma. The exact risk depends on which drugs and at what doses they are used.

The human immunodeficiency virus (HIV) can also weaken the immune system, and people infected with HIV are at increased risk of non-Hodgkin lymphoma.

Several genetic diseases can cause children to be born with a deficient immune system. Along with the risk of getting serious infections because of reduced immune defenses, these children also have an increased risk of developing non-Hodgkin lymphoma. Although these inherited immune deficiency diseases can be passed on to children, people with non-Hodgkin lymphoma who do not have these inherited diseases do not pass an increased risk of lymphoma on to their children.

Autoimmune Diseases

In autoimmune diseases, the immune system becomes abnormal, sees the person's own tissues as foreign, and tries to destroy them, as it would a germ. Some autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus (SLE, or lupus), and others have been linked with an increased rate of non-Hodgkin lymphoma.

Certain Infections

Lymphocytes (the types of cells from which lymphomas start) are part of the body's immune defenses. Several types of infections may raise the risk of non-Hodgkin lymphoma in different ways.

Infections that Directly Transform Lymphocytes

Some viruses can directly affect the DNA of lymphocytes, helping to transform them into cancer cells. The human T-cell leukemia/lymphoma virus (HTLV-1) and the Epstein-Barr virus (EBV) seem to work in this way.

Infection with HTLV-1 increases a person's risk of developing certain types of T-cell non-Hodgkin lymphoma. This virus is most common in some parts of Japan and in the Caribbean region, but is now found throughout the world. In the United States, it causes less than 1% of lymphomas. HTLV-1 spreads through sexual intercourse and contaminated blood and can be passed to children through breast milk from an infected mother.

In areas of Africa where Burkitt lymphoma is common, infection with the Epstein-Barr virus (EBV) is an important risk factor for this disease. In developed countries such as the United States, EBV is more often associated with lymphomas in patients infected with HIV. It has also been linked with developing nasal T-cell lymphoma and post-transplant lymphoma.

Infections that Weaken the Immune System

Infection with human immunodeficiency virus (HIV), also known as the AIDS virus, commonly causes immune system deficiency. HIV infection is a risk factor for developing certain types of non-Hodgkin lymphoma, such as Burkitt lymphoma and diffuse large B-cell lymphoma.

Infections that Cause Chronic Immune Stimulation

Some long-term infections may increase the risk of lymphoma by forcing a person's immune system to be on constant alert. As more lymphocytes are made to fight the infection, there is a greater chance that genetic mistakes can occur, which might eventually lead to lymphoma.

A type of bacteria, Helicobacter pylori, known to cause stomach ulcers, has also been linked to some lymphomas mucosa-associated lymphoid tissue (MALT lymphoma) of the stomach. The body's immune reaction to this infection increases the risk of non-Hodgkin lymphoma. The importance of this recent discovery is that antibiotics can help in treating some patients who have already developed lymphomas of the stomach due to H. pylori.

The hepatitis C virus (HCV) can also cause long-term infections. Recent reports have found that infection with HCV seems to be a risk factor for developing certain types of lymphoma.

Body Weight and Diet

Several studies have suggested that being overweight or obese may increase your risk of non-Hodgkin lymphoma. Some studies have also suggested that a diet high in vegetables may lower risk, although more research is needed to confirm this. In any event, maintaining a healthy weight and eating a healthy diet have many known health benefits outside of the possible beneficial effects on lymphoma risk.