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Understanding leukemia

Risk factors: what is known and what is not

After a leukemia diagnosis, almost everyone asks, “Why me? What did I do wrong?” The honest answer is that in most cases nobody knows the exact cause — and it is almost never the result of something a person or their family did. This topic explains which risk factors are proven, which are still uncertain, which are myths, and why a risk factor is not the same thing as a cause.

Last updated: ~8 min read
A translucent, glowing human figure in three-quarter view on a dark navy background; a faint DNA helix winds around the chest and bones, a few points on it picked out in soft amber light, with calm blood cells nearby.
Figure 1.Concept: risk factors shift the odds, but most leukemias begin with chance changes in DNA.

01Short answer

A risk factor is anything that raises the chance of getting a disease; it does not mean that it caused the disease in a particular person. For leukemia, the best-established risk factors are older age, earlier chemotherapy or radiation therapy, exposure to high doses of radiation, smoking (for AML), long-term exposure to benzene, certain inherited conditions such as Down syndrome, and — for CLL — a family history of CLL. Even so, most people with these risk factors never develop leukemia, and most people with leukemia have no known risk factor at all. Most of the DNA changes behind leukemia are acquired by chance during life and are not passed on to children. The role of power lines remains unclear; mobile phones, stress, injuries and ordinary foods are not proven causes. Leukemia is not contagious. Only a few risk factors can be changed, such as smoking and chemical exposure at work. If family risk worries you, a hematologist or genetic counsellor can advise.

02Simple explanation

A risk factor is something that makes a disease more likely — such as age, a chemical or an inherited condition. But having a risk factor does not mean you will get leukemia, and many people with leukemia have none of the known risk factors.

Leukemia starts when a blood-forming cell builds up changes in its DNA. In most people these changes happen by chance as cells divide over a lifetime — a kind of “copying error”. It is not a punishment, and it is not the result of anyone’s mistake.

The clearest risk factors are getting older, earlier cancer treatment (some chemotherapy drugs and radiation), smoking, long-term exposure to a chemical called benzene, and some inherited conditions, such as Down syndrome.

Most leukemias are not inherited. The DNA changes are usually found only in the leukemia cells, not in eggs or sperm, so they are not passed on to children. CLL runs in some families a little more often, but even then the absolute risk for relatives stays low.

Many fears are not supported by evidence: leukemia is not contagious, and mobile phones, stress, a knock or injury, or eating sugar have not been shown to cause it. If you feel guilty or the question “why?” keeps coming back, talking with your care team or a psychologist can help.

03Scientific explanation

According to the American Cancer Society (ACS), smoking is the only proven lifestyle-related risk factor for AML, and long-term exposure to benzene — found in some industries, in tobacco smoke and in gasoline — is also linked to AML. The NCI notes that benzene increases the risk of leukemia and other blood disorders. People exposed to high-dose radiation (for example, atomic-bomb survivors and people exposed in nuclear-reactor accidents) have a higher risk of AML, ALL and CML, while the risk from ordinary X-rays or CT scans is not well defined and is probably small. For CML, high-dose radiation is the only clearly established environmental risk factor; the Philadelphia chromosome is acquired during life and is not inherited (MedlinePlus Genetics).

Therapy-related myeloid neoplasms: some chemotherapy drugs raise the later risk of AML and MDS. After alkylating agents (such as cyclophosphamide), the risk usually shows up years after treatment, often together with MDS; after topoisomerase II inhibitors (such as etoposide or anthracyclines), it tends to appear sooner and often involves changes in the KMT2A gene. Radiation therapy adds to this risk as well. The benefit of treating the first cancer usually far outweighs this risk, but it is one of the reasons for long-term follow-up (NCI, ACS).

Inherited predisposition: in children, Down syndrome, Fanconi anemia, Li–Fraumeni syndrome, neurofibromatosis type 1, Noonan syndrome, Shwachman–Diamond syndrome, Diamond–Blackfan anemia, dyskeratosis congenita and other conditions raise the risk of AML or ALL (NCI). The identical twin of a child who develops ALL in the first year of life has a much higher risk (ACS). In adults, the 2022 WHO classification recognises myeloid neoplasms with germline predisposition — for example, inherited variants in the CEBPA, DDX41 or RUNX1 genes; when such a variant is suspected, genetic counselling is offered and related stem cell donors are checked too. First-degree relatives of people with CLL have a higher risk of CLL, and the ACS also lists exposure to the defoliant Agent Orange as linked to CLL.

Age-related precursor states: as we age, blood stem cells pick up mutations, and a small clone can expand without causing disease. Clonal hematopoiesis of indeterminate potential (CHIP), most often involving DNMT3A, TET2 or ASXL1, is found in about 5% of people aged 60–69 and nearly 10% of those aged 70–79, yet it progresses to a blood cancer in only about 0.5–1% of cases per year (ASH). Monoclonal B-cell lymphocytosis (MBL), a possible forerunner of CLL, is found in about 3% of adults over 40 and 6% of those over 60 (NCI). On power lines, the NCI reports mixed findings: most studies found no link, and a pooled analysis found a twofold risk only with very high magnetic-field exposure (≥0.4 µT), which affected fewer than 1% of the children studied.

04What happens in the body?

Age and chance: the biggest factors

Your body makes billions of blood cells every day, and each division carries a small chance of an error when DNA is copied. The body repairs most of these errors or removes the affected cells. But over the years changes build up, which is why most leukemias in adults appear after the age of 60. This is a natural biological process that nobody can control.

Close-up of a marrow cavity inside a translucent bone: among many healthy red and white cells sits a small group of soft violet cells, with a faint arc of light in the background resembling a clock hand.
Figure 2.With age, small clones of mutated cells can appear in the marrow; most of them never turn into disease.

A risk factor is not a cause

A risk factor shifts the odds across a large group of people, but it cannot explain why one particular person became ill. Most heavy smokers never develop AML, and many people with AML have never smoked. It also helps to tell relative risk from absolute risk: for example, if a risk rises from 1 in 10,000 to 2 in 10,000 people, that is a “doubling”, yet the risk is still very small.

What can be reduced?

There are only a few risk factors you can change, but they exist. Stopping smoking lowers the risk of AML as well as many other cancers. People who work with benzene or other chemicals should follow workplace safety rules. Medical scans that use radiation are done only when needed, and their benefit usually outweighs the small risk. For most leukemias, however, there is no known way to prevent them today.

A soft blue-gold shield of light surrounding a translucent human silhouette on a dark navy background; pale, scattered particles stay outside the shield, while calm, healthy blood cells float inside.
Figure 3.Steps such as stopping smoking and protection at work can reduce some risks.

Family and genetics: when to think about them

If several relatives have had blood cancers, if cancers appeared at a young age, or if there is a history of long-standing low platelets or congenital syndromes, a hematologist may suspect an inherited predisposition and offer genetic counselling. This matters especially when a relative is being considered as a stem cell donor. Whether family members should be tested is a decision best made together with a specialist.

05From risk to disease: the path rarely reaches the end

Four steps from a risk factor to leukemia — and the body’s protective mechanisms along the way.

Exposure or inheritance — Age, radiation, benzene, chemotherapy, an inherited variant.1Exposure or inheritanceAge, radiation, benzene, chemotherapy, an inherited variant.
DNA change — A chance or damage-related mutation in a stem cell.2DNA changeA chance or damage-related mutation in a stem cell.
The body’s controls — Repair, cell death, immune surveillance — usually enough.3The body’s controlsRepair, cell death, immune surveillance — usually enough.
Rarely, leukemia — When several changes come together in one cell.4Rarely, leukemiaWhen several changes come together in one cell.
Most never get illMost people with risk factors never develop leukemia.
Usually chanceMost mutations are acquired, not inherited.
Some risk can be reducedStopping smoking, protection at work.

06Leukemia risk factors: how strong is the evidence?

FactorLinked to which leukemias?EvidenceComment
Older ageAML, CLL, CMLProvenMost adult leukemias occur after 60
Earlier chemotherapy or radiation therapyAML, MDSProvenThe benefit of treatment usually outweighs the risk
High-dose radiationAML, ALL, CMLProvenAtomic bombs, reactor accidents; ordinary X-ray risk is small
SmokingAMLProvenThe only proven lifestyle factor
Long-term benzene exposureAML, other blood disordersProvenIndustry, tobacco smoke, gasoline
Inherited syndromes and variantsAML, ALL (especially in children)ProvenDown syndrome, Fanconi anemia, CEBPA, DDX41, RUNX1 and others
CLL in the familyCLLProvenAbsolute risk is still low
HTLV-1 virusAdult T-cell leukemia/lymphomaProvenRare; found in certain regions
Power lines, magnetic fieldsChildhood leukemiaUnclearFindings are mixed
Mobile phones, stress, injury, sugar—No evidenceNot shown to be causes

* This table is a simplified summary of ACS, NCI and ASH information. A risk factor describes probability, not the cause in an individual person. Discuss questions about your own situation with your hematologist.

07Key terms

Risk factor
Anything that raises the chance of getting a disease.
Relative risk
How many times higher the risk is in one group compared with another.
Absolute risk
The actual chance of getting a disease over a given time, for example 1 in 10,000.
Acquired (somatic) mutation
A DNA change that arises during life and is not inherited.
Inherited (germline) variant
A DNA change present in all cells from birth that can be passed on to children.
Benzene
A chemical found in industry, tobacco smoke and gasoline that raises leukemia risk.
Therapy-related AML
AML that develops after earlier chemotherapy or radiation therapy.
CHIP
Clonal hematopoiesis of indeterminate potential — an age-related, usually harmless clone of mutated cells.
MBL
Monoclonal B-cell lymphocytosis — a possible, usually harmless forerunner of CLL.
Genetic counselling
A conversation with a specialist about inherited risk and testing.

08Key points

  • A risk factor raises the odds but does not identify the cause in an individual.
  • Most people with leukemia have no known risk factor.
  • The strongest factors: age, earlier chemotherapy or radiation therapy, high-dose radiation, smoking, benzene and some inherited conditions.
  • Most leukemias are not inherited and are not passed on to children.
  • Leukemia is not contagious.
  • Mobile phones, stress, injury and sugar are not proven causes.
  • Stopping smoking and protection at work lower risk.
  • Talk to a hematologist or genetic counsellor about family risk.

09Frequently asked questions

Did I cause my leukemia?

Almost always, no. In most cases leukemia is caused by chance DNA changes that have nothing to do with lifestyle, diet or emotions. Even if you smoked, AML has many other causes, and the past cannot be changed — what matters now is treatment and support.

Will my children get leukemia?

Most leukemias are not inherited, because the DNA changes are found only in the leukemia cells. The exceptions are rare inherited syndromes and family predisposition; if one of these is suspected, your hematologist may offer genetic counselling.

Is leukemia contagious?

No. The NCI stresses that cancer does not spread from person to person. Hugging someone with leukemia, living in the same home or sharing dishes is safe. In fact, it is the patient who needs protecting from infections during treatment.

Can stress or an injury cause leukemia?

There is no evidence that they do. People sometimes remember a hard time or an injury before they became ill, but this is usually a coincidence. Stress does affect quality of life during treatment, though, so psychological support is worthwhile.

Should my relatives be tested?

In most cases relatives do not need any special tests. If several family members have had blood cancers or inherited syndromes, or if a relative is being considered as a stem cell donor, your hematologist may discuss genetic testing.

Can leukemia be prevented?

There is no known way to prevent most leukemias. Stopping smoking, avoiding benzene exposure and avoiding unnecessary radiation can reduce some risks. For childhood leukemia, there are no known preventive steps that parents could have taken.

10Questions for your doctor

Take these questions to your appointment. The ones you save are collected on the “My questions” page and stay on this device only.

  1. Do I have any known risk factor?

  2. Can the cause of my leukemia be identified?

  3. Do my family members need any tests?

  4. Is there anything in my lifestyle I should change?

My questions

12Sources

  1. American Cancer Society. Risk Factors for Acute Myeloid Leukemia (AML)
  2. American Cancer Society. Risk Factors for Acute Lymphocytic Leukemia
  3. American Cancer Society. Risk Factors for CLL
  4. American Cancer Society. Causes, Risk Factors, and Prevention of Childhood Leukemia
  5. National Cancer Institute (NCI). Risk Factors for Cancer
  6. National Cancer Institute (NCI). Benzene
  7. National Cancer Institute (NCI). Electromagnetic Fields and Cancer
  8. National Cancer Institute (NCI). Common Cancer Myths and Misconceptions
  9. National Cancer Institute (NCI). The Genetics of Cancer
  10. National Cancer Institute (NCI). Adult Acute Myeloid Leukemia Treatment (PDQ®) — Patient Version
  11. National Cancer Institute (NCI). Childhood Acute Myeloid Leukemia and Other Myeloid Malignancies Treatment (PDQ®) — Patient Version
  12. National Cancer Institute (NCI). Chronic Lymphocytic Leukemia Treatment (PDQ®) — Health Professional Version
  13. American Society of Hematology. Myeloid Malignancy Precursor Conditions (CHIP and related states)
  14. MedlinePlus Genetics (U.S. National Library of Medicine). Chronic myeloid leukemia
  15. Leukemia (Nature), Khoury et al. 2022. The 5th edition of the World Health Organization Classification of Haematolymphoid Tumours: Myeloid and Histiocytic/Dendritic Neoplasms
Medical disclaimerThis information is for educational purposes only and does not replace medical advice.
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