What Causes Leukemia: Risk Factors, Triggers and What You Can Change

The question usually arrives in a small voice, after the diagnosis has been said out loud: what did I do? A father wonders about the years he spent painting cars. A mother replays every ultrasound, every glass of wine before she knew. A retired teacher counts the decades of cigarettes she quit long ago. They are all looking for a cause, and they are all hoping it is something they could have controlled.

Medicine has a more complicated, and in some ways kinder, answer. Leukemia begins with damage to the genetic instructions inside a single blood-forming cell. Some of that damage has traceable origins. Much of it does not. Cells copy their DNA billions of times over a lifetime, and copying is never perfect.

This article sorts what the evidence actually shows about leukemia’s causes into three honest piles: what we know, what we suspect, and what turns out to be myth.

How does leukemia actually start in the body?

Picture the bone marrow as a factory that never closes. Every day it produces new red cells to carry oxygen, platelets to plug leaks, and white cells to fight infection, all descended from a small pool of blood stem cells. Each of those stem cells carries a full set of DNA instructions and follows a tightly regulated program: divide, mature, do a job, die on schedule.

Leukemia happens when one of those cells acquires changes in its DNA that break the program. According to the Mayo Clinic, the mutated cell keeps dividing when it should stop and refuses to die when it should. Its offspring are immature, dysfunctional white cells that pile up in the marrow and spill into the bloodstream, crowding out the healthy cells the body depends on.

That crowding explains the symptoms. Fewer red cells means fatigue and breathlessness. Fewer platelets means bruising and bleeding. Fewer working white cells means infections that linger. The cancer is not a lump you can feel; it is a takeover of a supply chain.

Two details matter for the cause question. The mutations are almost always acquired during a person’s lifetime rather than inherited, and more than one is usually needed. A single “hit” rarely produces leukemia on its own. This is why age is such a powerful risk factor for many types: the longer cells keep copying themselves, the more chances there are for the wrong combination of errors to accumulate in the same cell.

Is leukemia hereditary, or does it just run in some families?

Most people with leukemia have no relative with the disease, and most children of a parent with leukemia never develop it. The DNA changes that drive leukemia usually arise in bone marrow cells during life and are not present in the egg or sperm, so they cannot be passed on.

Inheritance does play a role at the edges. The NHS notes that having a close relative with chronic lymphocytic leukemia (CLL) modestly raises a person’s chance of developing it, which points to inherited variations that make the disease slightly more likely without making it inevitable. Several rare inherited syndromes carry a clearer signal. Down syndrome, Fanconi anemia, Li-Fraumeni syndrome and a handful of other conditions involve gene changes that affect how cells repair DNA or control growth, and the Mayo Clinic lists these genetic disorders among established risk factors.

What the evidence does not support is the idea that leukemia is a “family disease” in the way that some inherited cancers are. A grandmother’s diagnosis is worth mentioning to your doctor, particularly for CLL, but it is not a prophecy. If several relatives across generations have had blood cancers, or if leukemia appeared at an unusually young age in your family, a referral for genetic counseling can clarify whether an inherited syndrome is present. For most families, the honest answer is that shared genes contributed a little and chance contributed a lot.

Does radiation cause leukemia?

Radiation is the best-established environmental cause of leukemia, and the evidence comes from tragedy. Survivors of the atomic bombings in Japan developed leukemia at higher rates than unexposed populations, with cases appearing within years of exposure, earlier than most solid cancers. People treated with radiotherapy for other cancers, and early radiologists who worked without shielding, showed the same pattern. The NHS lists exposure to high levels of radiation, including radiotherapy, among the known causes of acute myeloid leukemia.

The mechanism is direct. Ionizing radiation deposits enough energy to snap DNA strands. Blood stem cells divide often, and a broken strand repaired incorrectly can become exactly the kind of mutation that starts the leukemic process. The dose matters enormously. The risk seen in bomb survivors and radiotherapy patients reflects exposures far above anything in ordinary life.

This is where fear often outruns the facts. Medical imaging such as X-rays and CT scans does deliver ionizing radiation, and doctors take that seriously by ordering scans only when the information is needed. The evidence shows any added risk from an individual scan is very small, while the risk of a missed diagnosis is real. Airport scanners, microwave ovens and cell phones emit non-ionizing radiation, which does not have the energy to break DNA bonds; no credible mechanism or consistent evidence links them to leukemia. Radiation deserves respect, not dread, and the distinction between ionizing and non-ionizing is the whole story.

Can chemicals like benzene cause leukemia?

Benzene has the dubious honor of being one of the few chemicals firmly linked to a specific cancer. It is a colorless liquid found in crude oil, gasoline and cigarette smoke, and historically it was used as a solvent in rubber manufacturing, printing, shoe-making and chemical plants. Workers with heavy, prolonged exposure developed acute myeloid leukemia at higher rates, and both the NHS and the Mayo Clinic list benzene among recognized causes.

Once inhaled or absorbed, benzene is broken down in the liver into by-products that travel to the bone marrow, where they damage DNA and interfere with the machinery that normally repairs it. The marrow is uniquely vulnerable because its cells divide so rapidly. Regulations in most countries now restrict workplace benzene levels sharply, and the exposures that produced the clearest evidence are rare in modern, well-run industries.

Other chemicals sit in the “suspected” pile. Formaldehyde, some pesticides and certain solvents have been studied for decades with mixed results: some studies show associations, others do not, and dose and duration are hard to reconstruct. That inconsistency is meaningful. It suggests any risk is small or confined to heavy occupational exposure rather than to the trace amounts encountered at home or in a garden.

If you have worked around fuels, solvents or industrial chemicals, tell your doctor. It will not change your diagnosis, but it helps your care team understand your history and may matter for workplace health records.

Does smoking cause leukemia?

Ask people what smoking causes and they will say lung cancer, then heart disease, then perhaps a shrug. Leukemia rarely makes the list, yet the link is well documented. The Mayo Clinic identifies smoking as a risk factor for acute myeloid leukemia, and the NHS includes it in its list of AML causes.

The connection runs partly through benzene. Cigarette smoke is one of the most common everyday sources of the chemical, and a smoker’s marrow receives a steady low-dose supply. Tobacco smoke also contains dozens of other compounds known to damage DNA, and the lungs deliver them efficiently into the bloodstream, where they circulate past the marrow with every heartbeat.

This matters because smoking is the one leukemia risk factor most people can actually change. It is also the one that quietly compounds. A person who smokes and works around fuels is stacking two benzene sources. A person who smokes and has received chemotherapy in the past adds tobacco’s DNA damage to treatment-related damage. Quitting does not undo mutations already acquired, but it stops new ones from accumulating, and the body’s DNA repair systems continue working in the background.

The tone here should be honest rather than scolding. Most smokers never develop leukemia, and many people with AML never smoked. The point is not blame. It is that among all the causes on this list, this is the lever that sits within reach.

Can chemotherapy or radiotherapy for another cancer cause leukemia?

This is one of the harder truths in oncology. Treatments designed to kill cancer cells work by damaging DNA or blocking cell division, and healthy bone marrow cells are caught in the crossfire. In a small proportion of people, that damage produces a second, unrelated cancer in the blood. Doctors call it therapy-related leukemia, and it most often takes the form of acute myeloid leukemia or a precursor condition called myelodysplastic syndrome. The Mayo Clinic lists previous chemotherapy and radiation therapy among established risk factors.

Certain classes of chemotherapy carry more of this risk than others because of how they interact with DNA, and combining chemotherapy with radiation to areas rich in marrow raises it further. Your oncologist weighs these considerations when designing treatment, which is why decisions about specific medications belong with the prescribing clinician who knows the full picture.

Therapy-related leukemia does not appear immediately; it develops over time, which is why follow-up care continues long after the original cancer is gone. Blood counts checked at routine visits are partly looking for this.

Perspective is essential. The treatments that carry this risk have allowed enormous numbers of people to survive cancers that were once fatal, and the added chance of a second cancer is small compared with the benefit of treating the first. Knowing about the risk is not a reason to fear treatment. It is a reason to keep showing up for follow-up appointments.

Which blood disorders can turn into leukemia?

Leukemia sometimes announces itself years in advance through a related condition. Myelodysplastic syndromes, in which the marrow produces abnormal, poorly functioning blood cells, can progress to acute myeloid leukemia in a proportion of people. Myeloproliferative neoplasms, where the marrow overproduces one cell type, carry a similar potential to transform. The NHS names these blood disorders among conditions that increase AML risk, and Cleveland Clinic describes them as part of the same family of marrow diseases.

The biology is a continuum rather than a switch. In these disorders, a population of marrow cells has already acquired some of the mutations on the road to leukemia. They behave abnormally but not yet catastrophically. If additional mutations accumulate, the balance can tip.

Aplastic anemia, in which the marrow fails to produce enough cells of any type, is also associated with a raised risk, likely because the stressed marrow that remains is working overtime and copying DNA under pressure.

For people living with one of these conditions, this is not a countdown. Many never progress. It does mean regular monitoring of blood counts is genuinely useful, because a change in the pattern can be detected early. Hematologists watch these disorders closely for exactly this reason, and the decision about when and whether to intervene rests with them.

Why does age matter so much, and are men at higher risk?

Leukemia has a strange age curve. The MedlinePlus notes that it is the most common cancer in children, with acute lymphoblastic leukemia dominating in early childhood. Then the numbers dip through young adulthood before climbing steeply. The NHS reports that chronic lymphocytic leukemia mostly affects people over 60 and is rare under 40, and that it is more common in men than women.

Two different mechanisms explain the two peaks. Childhood leukemia is thought to begin with a mutation acquired before birth, during the rapid cell division of fetal development, which is followed by a second event in early childhood. Adult leukemias reflect the slow accumulation of errors across decades of marrow activity, combined with an aging immune system that is less effective at removing abnormal cells.

Sex differences are real but modest, and their causes are not fully understood. Hormonal influences, historical differences in occupational exposure and smoking rates, and genetic factors have all been proposed.

Leukemia type	Typical age group	Best-established risk factors
Acute lymphoblastic (ALL)	Young children; also adults	Down syndrome and other genetic syndromes, prior radiation
Acute myeloid (AML)	Mainly older adults	Radiation, benzene, smoking, prior cancer treatment, blood disorders
Chronic lymphocytic (CLL)	Mostly over 60	Older age, male sex, family history
Chronic myeloid (CML)	Mainly adults	Radiation; most cases have no identified cause

The table is a map of probabilities, not destinies. Plenty of people fall outside every box.

What about the Philadelphia chromosome and other gene changes?

Some leukemias have a signature so specific it can be seen under a microscope. In most cases of chronic myeloid leukemia, a piece of chromosome 9 and a piece of chromosome 22 have swapped places. The result, named the Philadelphia chromosome after the city where it was first described, fuses two genes into one abnormal instruction that tells the cell to grow continuously. Johns Hopkins Medicine describes this kind of chromosomal change as central to how the disease develops.

The Philadelphia chromosome is not inherited. It arises spontaneously in a single marrow cell, for reasons that remain unclear in the vast majority of people, and every leukemic cell that follows is a copy carrying the same error. Understanding this single fusion transformed the field, because it identified a precise molecular target. Medicines that block the fused protein’s signaling have changed the outlook for this disease; how they are used, and for how long, is a decision for the treating hematologist.

Similar stories play out across other leukemias. Acute leukemias are now classified partly by which genes are mutated or rearranged, because those changes predict how the disease behaves and how it responds. Some mutations affect genes that control cell growth; others disable the cell’s self-destruct program; others disrupt the process of maturing from a stem cell into a functioning white cell.

For the cause question, this genetic detail delivers a clear message. The “cause” of leukemia is, at the cellular level, always a mutation. What varies is whether we can trace what produced it.

Things people blame for leukemia that the evidence does not support

Fear fills gaps in knowledge, and leukemia has many gaps. Several suspected causes have been studied thoroughly enough to be set aside.

Cell phones, Wi-Fi and microwaves emit non-ionizing radiation that lacks the energy to break DNA. Decades of research have found no consistent link to leukemia, and no plausible biological mechanism has been demonstrated. Power lines have a more tangled history: a few early studies suggested a weak association between high magnetic-field exposure and childhood leukemia, but later research has been inconsistent, no mechanism has been established, and mainstream health bodies do not classify this as a proven cause.

Stress, grief and “negative thinking” do not cause leukemia. The Mayo Clinic and other major sources do not list psychological factors among risk factors, and studies looking for such a link have not found one. Sugar does not feed a leukemia that would otherwise not exist. Every cell in the body uses glucose; cutting it does not selectively starve cancer cells.

Infections attract suspicion because childhood leukemia often follows a common illness. The current scientific thinking is more nuanced: some researchers propose that a delayed or unusual pattern of immune exposure in early life may be one contributing factor among many, but this remains a hypothesis under study, not an established cause. Hair dye, artificial sweeteners and fluoridated water have all been examined and have not shown convincing links.

Setting these aside is not dismissiveness. It frees attention for the factors that genuinely matter.

Can you prevent leukemia? What you can actually change

Here is the uncomfortable truth first: most leukemia cannot be prevented, because most cases have no identifiable cause. There is no screening test for the general population and no diet or supplement shown to stop it. Anyone selling certainty on this point is selling something.

Within those limits, a few choices genuinely shift the odds. Not smoking, or stopping if you do, removes a documented cause of acute myeloid leukemia and cuts off a daily source of benzene. Following workplace safety rules around fuels, solvents and industrial chemicals, including wearing the protective equipment provided and using ventilation, reduces the occupational exposures that produced the clearest evidence of harm. The NHS singles out both smoking and benzene as modifiable exposures.

Medical radiation belongs in this list with a caveat. Asking whether a scan is necessary is reasonable; refusing a scan your doctor recommends usually trades a very small theoretical risk for a much larger real one. Keeping a personal record of imaging can help clinicians avoid unnecessary repeats.

Some studies have suggested an association between excess body weight and certain leukemias, though the evidence is less consistent than for other cancers and the mechanism is unclear. Maintaining general health supports the immune system that helps clear abnormal cells, which is a sound reason for good habits even without a leukemia-specific guarantee.

What you cannot change, including your age, your genes and the treatment you received for a past cancer, deserves acknowledgment rather than guilt. Knowing your risk profile helps you and your doctor pay attention to the right symptoms.

What is one of the first signs of leukemia?

Leukemia rarely arrives with a dramatic symptom. It arrives with an ordinary one that refuses to leave. Tiredness that sleep does not fix is the most common early complaint, and it is easy to blame on work, parenting or age. According to the Mayo Clinic, other early signs include fever or chills, frequent or severe infections, easy bruising or bleeding, tiny red spots in the skin called petechiae, swollen lymph nodes, unexplained weight loss, bone or joint pain, night sweats and a feeling of fullness under the left ribs from an enlarged spleen.

Each symptom traces back to the marrow takeover described earlier. Fatigue and pallor reflect too few red cells. Bruising from minor knocks, nosebleeds that take a long time to stop, or gums that bleed when brushing reflect too few platelets. Infections that keep coming back, or a cold that turns into something worse, reflect white cells that exist in large numbers but cannot do their job.

Chronic leukemias often produce no symptoms at all in their early stages. The NHS notes that CLL is frequently discovered by chance when a blood test is done for another reason. This is worth knowing, because it means an unexpected abnormal blood count deserves follow-up even when a person feels well.

None of these symptoms is specific to leukemia. Fatigue has a hundred causes, most of them benign. The pattern that should raise attention is combination and persistence: several of these signs together, lasting weeks rather than days, without an obvious explanation.

When should you see a doctor about possible leukemia symptoms?

Most people who worry about leukemia do not have it, and a doctor’s visit is how that worry gets resolved. A simple complete blood count, drawn from the arm and analyzed within hours, will show whether the numbers of red cells, white cells and platelets are normal. When they are, which is usually the case, the search for another explanation begins. When they are not, a hematologist can examine the cells more closely.

Make an appointment without delay if you notice a combination of the following: persistent fatigue or breathlessness that is new for you, bruises appearing without injury or in unusual places, bleeding that is hard to stop, tiny red or purple dots on the skin, repeated infections or a fever that keeps returning, swollen glands in the neck, armpits or groin that do not shrink over a few weeks, drenching night sweats, unexplained weight loss, or persistent bone pain. In children, watch also for pale skin, irritability, limping or reluctance to walk, and a swollen abdomen.

Seek urgent care the same day for red-flag signs: a high fever with shaking chills, especially alongside recent unexplained bruising; bleeding that will not stop; sudden severe headache, confusion or vision changes; or extreme breathlessness. These can indicate dangerously low blood counts or infection in someone whose immune system is not working, and they need assessment quickly.

Bring a list of your symptoms, when they started, any past cancer treatment, workplace chemical exposures, and family history. The Cleveland Clinic emphasizes that diagnosis rests on blood tests and, where needed, a bone marrow sample; no symptom on its own is proof of anything.

What to do if you are diagnosed with leukemia, and can it be healed?

The first thing to do is breathe, and the second is to ask which type you have. Leukemia is not one disease. Acute and chronic forms behave differently, as do lymphoid and myeloid forms, and within each category the specific genetic changes in your cells shape everything that follows. Before any decisions are made, your team will run tests to define the subtype precisely. That waiting period can feel unbearable, but it is time well spent.

Outcomes vary widely, and honesty serves you better than reassurance. Some leukemias are treated with the realistic goal of long-term remission, and many people go on to live full lives. Others are managed as long-term conditions. The NHS notes that early-stage CLL often requires no immediate treatment at all, with regular monitoring instead, and that some people live for many years with the condition. Acute leukemias require prompt treatment, and their outlook depends heavily on age, overall health and the genetic features of the disease. Your hematologist can give you a picture that is specific to you; general statistics cannot.

Practical steps help. Bring someone to appointments to take notes. Ask how the treatment plan will be decided and what each phase is trying to achieve. Ask about clinical trials if they are appropriate. Report every new symptom, especially fever, because a compromised immune system changes what counts as minor. Accept help from family, friends and support services.

Whether leukemia can be “healed” is a question with no universal answer. Whether it can be treated, understood and lived with is a question the evidence answers more encouragingly than it did a generation ago.

Frequently asked questions

What is the main cause of leukemia?

There is no single main cause; leukemia results from acquired DNA mutations in blood-forming cells, and in most people the trigger for those mutations is never identified. Established risk factors include ionizing radiation, benzene exposure, smoking, prior chemotherapy or radiotherapy, certain blood disorders, some inherited genetic conditions, older age and family history. Many people with leukemia have none of these, and many people with several of them never develop the disease.

What is one of the first signs of leukemia?

Persistent fatigue that rest does not relieve is one of the most common early signs, along with unexplained bruising or bleeding, frequent infections, fever, swollen lymph nodes, night sweats and bone pain. These reflect the marrow producing too few healthy red cells, platelets and working white cells. Chronic leukemias often cause no symptoms early on and are found incidentally on blood tests. Several of these signs together, lasting weeks, warrant a doctor’s visit.

Can leukemia be healed?

It depends on the type, and no honest answer applies to everyone. Some leukemias are treated with the goal of long-term remission and many people live full lives afterward; others are managed as long-term conditions with periods of monitoring and treatment. Outcomes vary with age, general health and the specific genetic features of the disease. Your hematologist can describe the realistic goals of treatment for your particular subtype far better than general statistics can.

How long can you live with leukemia?

Survival ranges from months to decades depending on the type and individual factors, so no single figure is meaningful. The NHS notes that early-stage chronic lymphocytic leukemia often needs no immediate treatment and that some people live for many years with it. Acute leukemias progress quickly without treatment but can respond well to prompt care. Age, overall health and the genetic profile of the leukemic cells all shape the outlook; ask your care team for your specific picture.

What to do if you get leukemia?

Start by learning your exact subtype, because acute, chronic, lymphoid and myeloid leukemias are treated very differently and testing to define yours comes before any decisions. Bring someone to appointments, write down questions, ask what each stage of treatment aims to achieve, and report every new symptom promptly, especially fever. Accept practical and emotional support. Treatment choices, including specific medications, belong with your hematology team, who know your full medical picture.

Is leukemia hereditary?

Usually not. Most leukemia arises from mutations acquired in bone marrow cells during a person’s life, which cannot be passed to children. A family history of chronic lymphocytic leukemia modestly raises risk, and rare inherited syndromes such as Down syndrome, Fanconi anemia and Li-Fraumeni syndrome increase it more clearly. If several relatives have had blood cancers or leukemia appeared at an unusually young age, genetic counseling can help clarify whether an inherited condition is present.

Can radiation from X-rays or CT scans cause leukemia?

The evidence shows any added risk from an individual medical scan is very small, and far outweighed by the risk of missing a diagnosis when imaging is needed. The clear links between radiation and leukemia come from very high exposures such as atomic bomb survivors and therapeutic radiotherapy. Doctors order scans only when the information matters and use the lowest practical dose. Asking whether a scan is necessary is reasonable; refusing recommended imaging usually is not.

Does smoking cause leukemia?

Yes, smoking is a documented risk factor for acute myeloid leukemia according to the Mayo Clinic and the NHS. Cigarette smoke contains benzene, a chemical firmly linked to this leukemia, along with many other DNA-damaging compounds that the lungs deliver directly into the bloodstream and past the bone marrow. Most smokers never develop leukemia and many people with AML never smoked, but smoking remains the most changeable risk factor on the list.

Can stress cause leukemia?

No. Major medical sources including the Mayo Clinic do not list stress, grief or emotional strain among leukemia risk factors, and studies looking for such a connection have not found one. Leukemia is caused by DNA changes in blood-forming cells, and there is no demonstrated mechanism by which psychological stress produces those changes. Stress can certainly worsen how a person copes with illness, which is a good reason to seek support, but it does not cause the disease.

Can leukemia be prevented?

Most cases cannot be prevented because most have no identifiable cause, and no screening test exists for the general population. A few choices do reduce risk: not smoking, following workplace safety rules around benzene-containing fuels and solvents, and avoiding unnecessary radiation exposure. Factors such as age, genetics and prior cancer treatment cannot be changed, but knowing your risk profile helps you and your doctor stay alert to symptoms that deserve a blood test.

References

• NHS – Acute myeloid leukaemia: Causes
• NHS – Chronic lymphocytic leukaemia
• MedlinePlus – Leukemia
• Cleveland Clinic – Leukemia

This article is for general information only and is not a substitute for professional medical advice. Please consult a qualified doctor about your individual situation.