Causes and Risk Factors of Chronic Lymphocytic Leukemia

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Chronic lymphocytic leukemia (CLL) starts in the bone marrow’s white blood cells, specifically the lymphocytes. While the exact cause of CLL isn’t known, experts do know that genes play a role. Risk factors like age and exposure to chemicals may also contribute to the development of this type of cancer.

This article will discuss the causes and risk factors of chronic lymphocytic leukemia.

Doctor talking with patient

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Common Causes 

Lymphocytes are a type of white blood cell that forms from stem cells in the bone marrow, the spongy tissue inside the bones. They then make their way to your lymphatic system, where they help fight off invaders like bacteria, viruses, fungi, or parasites.

When something goes wrong in the production of these white blood cells, cancer can occur. In the case of CLL, genetic mutations cause the out-of-control production of lymphocytes.

These can't fight off infection like normal white blood cells. And, this proliferation also hampers platelet (cells involved in clotting) and red blood cell production in the bone marrow, causing additional symptoms.

What Are the Symptoms of CLL?

Because CLL is a chronic leukemia, some people may not notice symptoms right away. Or symptoms may be vague and generalized. These include:

  • Fever
  • Unexplained weight loss
  • Night sweats
  • Swollen lymph nodes
  • Easy bruising
  • Easy bleeding
  • Frequent infections
  • Swelling in the abdomen

Some risk factors that may increase your chances of developing CLL include:

  • Being over 50: Almost 90% of people with CLL fall into this age group. 
  • Chemical exposures: Evidence has linked exposure to some herbicides, like Agent Orange, to an increased risk of CLL. Exposure to other chemicals, like radon, may also be linked to CLL. Radon is a radioactive gas that you can neither smell nor see. It originates from the ground and can enter homes through cracks or openings.
  • Having a close relative with CLL: If you have a close blood relative with CLL, you have a twofold risk of developing it yourself.
  • Being male: The risk for developing CLL is slightly higher in males compared to females.
  • Being White: White populations of both North America and Europe are more likely to develop this form of cancer than people of other ethnic groups.

Keep in mind that having any of these risk factors doesn’t mean you’ll definitely develop CLL. A risk factor is just that: something that may increase your risk. Research may show that some of these factors are linked to developing CLL, but why there is a link isn't clear in most cases.

What Is Agent Orange?

Agent Orange is an herbicide (weed killer) that is most known for its use in clearing leaves and plant growth during the Vietnam War. This herbicide contains a dangerous substance called dioxin. The chemical has been linked to a variety of adverse effects, including:

  • Some types of cancers
  • Congenital (present at birth) conditions or other disabilities
  • Diabetes


It's rare for people to inherit genetic mutations that then cause CLL. 

CLL is typically caused by noninheritable genetic mutations. These mutations are not present at conception but develop in cells afterward. Unless they occur in cells that form eggs or sperm, they are not passed on to the person's descendants.

Often, people with CLL have a mutation in their chromosomes—typically a deletion in chromosome 13. Other chromosomes that may be affected include chromosomes 11 and 17. However, experts don't quite know why these changes occur, which genes are involved, or why these mutations cause leukemia. 

Evidence suggests that B lymphocytes may start to divide uncontrollably after reacting to a substance called an antigen—these may include things like germs or proteins foreign to the body. Experts aren't sure why this happens, though.

Lifestyle Risk Factors 

To reduce your risk of exposure to radon, you can have your home tested and have repairs done if radon levels are high. Dioxin production has been greatly reduced in the United States, but it can persist in the environment, including in the water supply. Other than avoiding exposure to dioxin-containing chemicals or radon, there are no known lifestyle risk factors for CLL.

What Is a Lifestyle Risk Factor?

A lifestyle risk factor is a risk factor that you have control over. Things like smoking or being active are considered lifestyle risk factors. Lifestyle factors can greatly influence your chance of developing certain cancers.


Chronic lymphocytic leukemia happens due to gene mutations affecting the cells in the bone marrow that produce lymphocytes. These changes cause healthy bone marrow cells to grow out of control. The reason for these mutations is unknown. However, experts have identified some risk factors, including chemical exposure, age, and sex. 

A Word From Verywell

Knowing the exact cause of specific cancers would likely help researchers improve existing treatment options. Unfortunately, experts still haven’t identified a precise cause of CLL. 

That said, we do know that some risk factors may increase your chance of developing this type of blood cancer. Additional research may help identify more risk factors, but there is no known way to prevent CLL for now. 

9 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. American Society of Hematology. Blood cancers.

  2. American Cancer Society. Signs and symptoms of chronic lymphocytic leukemia.

  3. American Cancer Society. What are the risk factors for chronic lymphocytic leukemia?

  4. American Lung Association. Radon basics.

  5. MedlinePlus. Chronic lymphocytic leukemia.

  6. Aspen Institute. What is agent orange?

  7. American Cancer Society. Do we know what causes chronic lymphocytic leukemia?

  8. Environmental Protection Agency. Learn about dioxin.

  9. Leukemia & Lymphoma Society. Chronic lymphocytic leukemia.

By Steph Coelho
Steph Coelho is a freelance health writer, web producer, and editor based in Montreal. She specializes in covering general wellness and chronic illness.