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What Are the Risk Factors for Chronic Lymphocytic Leukemia?

A risk factor is something that affects a person's chance of getting a disease like cancer. Different cancers have different risk factors. Some risk factors, like smoking, can be changed. Others, like a person’s age or family history, can’t be changed.

But risk factors don't tell us everything. Having a risk factor, or even many risk factors, doesn’t mean that you will get the disease. And some people who get the disease may not have had any known risk factors. Even if a person has a risk factor and develops cancer, it's often very hard to know how much that risk factor may have contributed to the cancer.

There are very few known risk factors for chronic lymphocytic leukemia (CLL). These include:

  • Age
  • Exposure to certain chemicals
  • Family history
  • Sex
  • Race/ethnicity

The risk of CLL does not seem to be linked to smoking, diet, or infections.


The risk of CLL goes up as you get older. About 9 out of 10 people with CLL are over age 50.

Certain chemical exposures

Some studies have linked exposure to Agent Orange, an herbicide used during the Vietnam War, to an increased risk of CLL. Some other studies have suggested that farming and long-term exposure to certain pesticides may be linked to an increased risk of CLL, but more research is needed to be sure.

Radon exposure at home has been linked to an increased risk.

Family history

First-degree relatives (parents, siblings, or children) of people with CLL have more than twice the risk for this cancer.


CLL is slightly more common in males than females. The reasons for this are not known.


CLL is more common in North America and Europe than in Asia. Asian people who live in the United States do not have a higher risk than those living in Asia. This is why experts think the differences in risk are related to genetics rather than environmental factors.

The American Cancer Society medical and editorial content team

Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.

American Society of Clinical Oncology. Leukemia - Chronic Lymphocytic - CLL: Risk Factors (06/2016). Accessed at on April 12, 2018.

National Cancer Institute. Chronic Lymphocytic Leukemia Treatment (PDQ®)–Patient Version. March 28, 2018. Accessed at on April 12, 2018.

Oancea SC, Rundquist BC, Simon I, et al. County level incidence rates of chronic lymphocytic leukemia are associated with residential radon levels. Future Oncol. 2017;13(21):1873-1881.

Last Revised: May 10, 2018