Leukemia develops when bone marrow starts making blood cells that grow out of control
Leukemia happens when something goes wrong in your bone marrow — the spongy tissue inside your bones where blood cells are made. Normally, your bone marrow produces red blood cells, white blood cells, and platelets in a careful, controlled way. With leukemia, the marrow starts making white blood cells that multiply too fast and don't work the way they should. These abnormal cells crowd out the healthy ones, which is what causes the symptoms and problems leukemia brings.
The truth is that doctors often cannot point to a single cause. Leukemia is not something you catch from another person, and in most cases it is not something you inherited. Instead, it appears to result from a combination of factors — some you are born with, some that happen during your life, and some that may just be chance.
Key Takeaways
- Leukemia starts when bone marrow produces white blood cells that multiply uncontrollably and crowd out healthy blood cells.
- Most people who develop leukemia have no known family history and no clear single cause.
- Certain exposures — including high-dose radiation, some chemicals, and some viruses — raise the risk, but most people exposed to these do not develop leukemia.
- Some genetic conditions present from birth increase leukemia risk, though most people with these conditions never develop it.
- Doctors identify leukemia through blood tests and bone marrow biopsy, not by finding what caused it.
Radiation exposure and leukemia risk
High-dose radiation is one of the few exposures clearly linked to leukemia. This includes radiation from cancer treatment, nuclear accidents, or atomic weapons testing — not the small amounts from medical X-rays or airport security scanners. People who survived the atomic bombs dropped on Japan in 1945 showed increased leukemia rates years afterward. Cancer patients who received radiation therapy also have a higher risk.
The risk depends on how much radiation you received and when. Children exposed to radiation are at higher risk than adults. The time between exposure and leukemia diagnosis can be years or even decades, which is why doctors ask about your history of radiation when you are first diagnosed.
Chemical exposures that may increase risk
Benzene, a chemical used in manufacturing and found in gasoline, has been linked to leukemia in people exposed to high levels over many years. Workers in certain industries — oil refining, rubber manufacturing, and some chemical plants — face higher exposure. Formaldehyde, used in building materials and some medical products, has also been studied as a possible risk factor, though the evidence is less clear than it is for benzene.
Again, exposure does not mean you will develop leukemia. Most people who work with these chemicals do not get the disease. The risk appears to depend on how much you were exposed, for how long, and possibly on your individual genetics.
Genetic conditions you are born with
Some people inherit genetic conditions that raise their leukemia risk from birth. Down syndrome (also called trisomy 21) carries a higher risk of acute leukemia in children. Fanconi anemia, a rare inherited disorder affecting bone marrow, also increases risk. Neurofibromatosis type 1, a condition affecting nerve tissue growth, is another example.
Having one of these conditions does not mean you will develop leukemia — most people with Down syndrome or Fanconi anemia never do. But the risk is measurably higher than in the general population, which is why doctors may recommend more frequent screening for people with these diagnoses.
Certain viruses and infections
A virus called HTLV-1 (human T-cell leukemia virus type 1) can cause a rare form of adult leukemia in people who are infected. This virus is found mainly in parts of Japan, the Caribbean, and Africa. Most people infected with HTLV-1 never develop leukemia, even after decades.
HIV, the virus that causes AIDS, also raises leukemia risk — though modern HIV treatment has reduced this risk significantly. Other viral infections have been studied, but the evidence linking them to leukemia is weaker or still unclear.
Previous cancer treatment and leukemia
Some people who receive chemotherapy or radiation for another cancer later develop leukemia as a side effect. This is called therapy-related leukemia or secondary leukemia. It can happen months or years after the original cancer treatment ends. The risk is higher with certain chemotherapy drugs and with combined chemotherapy and radiation.
Doctors weigh this risk against the benefit of treating the original cancer. Modern treatment plans try to balance effectiveness against long-term side effects, and the risk of therapy-related leukemia is one factor in those decisions.
Age, smoking, and other factors
Leukemia can develop at any age, but some types are more common in children and others in older adults. Chronic myeloid leukemia (CML) and chronic lymphocytic leukemia (CLL) are more common as people age. Acute lymphoblastic leukemia (ALL) is the most common leukemia in children.
Smoking has been studied as a possible risk factor, and some research suggests it may modestly raise the risk of certain leukemias. Obesity and alcohol use have also been examined, but the evidence is not as strong as it is for radiation or benzene exposure. Being male appears to carry a slightly higher risk than being female for most types of leukemia, though doctors do not fully understand why.
Why most people with leukemia have no clear cause
The majority of people diagnosed with leukemia have no history of radiation exposure, chemical contact, genetic condition, or viral infection. In these cases, leukemia appears to develop from random changes in cells that happen over time. Your cells divide millions of times throughout your life, and occasionally a mistake occurs in the genetic instructions — a mutation. Usually your body catches and fixes these mistakes, or the abnormal cell dies. Sometimes it does not, and that cell multiplies into leukemia.
This is why leukemia is not your fault, and why it is not something you could have prevented by making different choices. Doctors focus on identifying and treating the leukemia itself rather than on finding a cause, because in most cases the cause cannot be found.
Frequently Asked Questions
Can you catch leukemia from someone else?
No. Leukemia is not contagious. You cannot catch it from a family member, friend, or anyone else who has it. The only exception is HTLV-1, a virus that can be transmitted through blood transfusion or sexual contact and may eventually cause leukemia in some infected people — but this is transmission of the virus, not the disease itself.
If my parent had leukemia, am I more likely to get it?
Most leukemias are not inherited. Having a parent with leukemia does not significantly raise your risk unless your family carries a specific genetic condition like Fanconi anemia or Li-Fraumeni syndrome. Talk to your doctor about your family history so they can assess your individual risk.
Does living near power lines or using a cell phone cause leukemia?
No clear evidence links either power lines or cell phones to leukemia. These concerns have been studied extensively, and major health organizations have found no proven connection. The radiation from power lines and cell phones is very different from the high-dose radiation known to increase leukemia risk.
Can stress cause leukemia?
Stress does not cause leukemia. While chronic stress can affect your immune system and overall health, it is not a known risk factor for developing leukemia. Leukemia develops from changes in bone marrow cells, not from emotional or psychological factors.
What should I tell my doctor about my history?
Tell your doctor about any significant radiation exposure (cancer treatment, nuclear accidents, or occupational exposure), long-term work with chemicals like benzene, family members with genetic conditions, and any known viral infections like HTLV-1 or HIV. This history helps your doctor understand your situation, though it will not change how leukemia itself is diagnosed or treated.