Chronic lymphocytic leukemia (CLL) is the most common type of adult leukemia in the United States.

Leukemia is a group of cancers that develop in blood cells. CLL develops in a type of white blood cell called lymphocytes. The rapid division of lymphocytes can crowd out healthy blood cells. Over time, this can lead to symptoms like:

  • anemia
  • abnormal bruising
  • frequent infections

The exact cause of CLL isn’t clear, but researchers have identified risk factors that seem to increase your chances of developing CLL. Read on to learn more.

The following have been identified as risk factors or potential risk factors for CLL.

Family history

A family history of CLL is the strongest known risk factor. It’s estimated that people with a parent, siblings, or child with CLL have an 8.5 times higher risk of developing CLL than somebody without a family history.


The risk of developing CLL rises exponentially with age and is highest among people over the age of 70. About 90 percent of people who develop CLL are over the age of 50.

The average age of onset is 72.

Exposure to chemicals

Exposure to certain chemicals may increase your risk of developing CLL.

One chemical associated with an increased risk of CLL is Agent Orange. This herbicide was used during the Vietnam War to clear leaves and vegetation. Production stopped in the United States in the 1970s.

In a 2018 study, researchers found Vietnam veterans exposed to Agent Orange developed CLL at a younger age than veterans not exposed to Agent Orange:

  • half of veterans exposed to Agent Orange who developed CLL were younger than 63.2
  • half of veterans not exposed to Agent Orange who developed CLL were younger than 70.5

The researchers found that Agent Orange exposure wasn’t associated with a poorer outlook.

Other studies have found evidence of a potential link between CLL and some other herbicides, pesticides, and agricultural agents. The frequency and duration of exposure to these chemicals are thought to contribute to the risk.

According to the American Cancer Society, rates of leukemia — particularly acute myeloid leukemia — are higher in workers exposed to high levels of benzene. Benzene is used in industries such as leather manufacturing, oil refining, and rubber manufacturing.

Although current evidence isn’t as strong, some studies suggest a link between benzene exposure and CLL.

Biological sex

The risk of developing CLL is about twice as high in men than in women, but it’s still unknown why men are at a higher risk.

In a 2019 study, researchers found evidence that differences in DNA methylation between sexes may play a role. DNA methylation is a process where a methyl group is added to a DNA molecule. It’s involved in many bodily functions and health problems.


Rates of CLL are higher in North America and Europe compared to Asia. CLL is most common in people who are white or of Eastern European, Russian, or Jewish descent.

Asian people in the United States have similar rates of CLL as Asian people living in Asia. This suggests that genetic factors contribute to racial differences.

CLL may have different outlooks in different races. Studies suggest that Black people may have poorer overall survival than other groups.

Researchers aren’t exactly sure what causes CLL. A combination of genetic and environmental factors likely contribute.

Like all forms of cancer, CLL develops when genetic mutations cause cells to replicate uncontrollably. In the case of CLL, these cells are a type of white blood cell called lymphocytes.

A loss of part of chromosome 13 is the most common genetic mutation in people with CLL. Loss of part of chromosomes 11 or 17 are also common. In some cases, there may be an extra chromosome 12.

Many of the risk factors for CLL, like your genes or biological sex, are out of your control. Most people with CLL have no known risk factors.

You may be able to lower your chances of developing CLL by:

  • avoiding contact with benzene
  • maintaining a healthy body weight
  • minimizing contact with some herbicides or pesticides
  • wearing protective clothing when you do come into contact with herbicides, pesticides, or other potentially carcinogenic chemicals

Does having CLL put you at high risk for COVID-19?

Research suggests that people with CLL may be more likely to develop COVID-19 due to advanced age, disease-related immunosuppression, and treatment-related immunosuppression.

Taking precautions, like wearing a mask in public spaces and getting vaccinated, can help you minimize your chances of developing illness or severe illness.

What are the common symptoms of CLL?

CLL may not cause any noticeable symptoms in the early stages. As it progresses, it may cause symptoms such as:

What are the treatment options for CLL?

Treatment for CLL depends on factors such as how far along your cancer has progressed and your overall health. Options include:

What’s the most common cause of death in CLL?

In a 2021 study, researchers found that the most common cause of death among people with newly diagnosed CLL was:

Cause of death in people with CLLPercentage
complications related to disease progression34.6%
second cancer16.4%
CLL-unrelated death20.6%

What’s the outlook for CLL?

The survival rate for CLL is higher than many other types of leukemia and cancer. Half of people diagnosed with CLL live at least 10 years. Some people live 20 years or more.

CLL is the most common type of adult leukemia in the United States. The exact cause of CLL isn’t clear, but researchers have identified some risk factors.

A family history of CLL is the strongest risk factor. Increased age, male sex, and exposure to some chemicals are among the other risk factors.

Many of the risk factors for CLL are out of your control. Avoiding or minimizing exposure to pesticides and herbicides and other potentially carcinogenic chemicals may help reduce your odds of developing CLL and some other cancers.