Leukemia doesn’t have a single cause. It develops when blood cells in your bone marrow acquire mutations in their DNA — specifically in genes that control how cells grow, divide, and die. These mutations cause abnormal white blood cells to multiply out of control, crowding out healthy blood cells. In most cases, we can’t point to one definitive trigger, but research has identified several factors that significantly increase your risk.
About 59,610 new cases of leukemia are diagnosed in the U.S. each year, according to the American Cancer Society. While some risk factors — like chemical exposures and smoking — are modifiable, others, like inherited genetic conditions, are not. Here’s what we actually know about what causes leukemia and what raises your risk.
How Leukemia Develops at the Cellular Level
Every blood cell in your body starts as a hematopoietic stem cell in the bone marrow. These stem cells differentiate into red blood cells, white blood cells, and platelets. Leukemia occurs when one of these cells acquires a genetic error — sometimes a chromosomal translocation, sometimes a point mutation — that gives it a survival or growth advantage.
That single mutated cell then divides rapidly, producing billions of dysfunctional clones. These leukemic cells don’t mature properly and can’t fight infections like normal white blood cells. They also accumulate in the marrow, suppressing normal blood cell production. That’s why patients develop anemia, infections, and bleeding problems.
The specific mutation determines the leukemia type. For example, the Philadelphia chromosome (a translocation between chromosomes 9 and 22) drives nearly all cases of chronic myeloid leukemia (CML). In Promyelocytic Leukemia: From Definition to…”>acute promyelocytic leukemia, a fusion of chromosomes 15 and 17 is the culprit.
The 7 Known Causes and Risk Factors of Leukemia
1. Chemical Exposure — Especially Benzene
Benzene is the most well-established chemical risk factor for leukemia, particularly acute myeloid leukemia (AML). It’s found in gasoline, industrial solvents, cigarette smoke, and certain manufacturing processes. Workers with prolonged benzene exposure have a 2- to 3-fold increased risk of AML. The International Agency for Research on Cancer (IARC) classifies benzene as a Group 1 carcinogen — meaning there’s sufficient evidence it causes cancer in humans.
2. Ionizing Radiation
High-dose radiation exposure is a proven leukemia trigger. Survivors of the Hiroshima and Nagasaki atomic bombings showed leukemia rates 5 to 15 times higher than the general population, with peak incidence occurring 6-8 years after exposure. Therapeutic radiation for other cancers also modestly increases leukemia risk, particularly for AML.
3. Previous Chemotherapy
Treatment-related leukemia accounts for roughly 10-20% of all AML cases. Alkylating agents (like cyclophosphamide) and topoisomerase II inhibitors (like etoposide) are the biggest offenders. This type of leukemia typically develops 2-10 years after the original cancer treatment and tends to carry a worse prognosis.
4. Smoking
Cigarette smoking increases AML risk by about 40%. The link is dose-dependent — the more pack-years, the higher the risk. Tobacco smoke contains benzene and formaldehyde, both of which damage bone marrow stem cells. This is one of the few modifiable causes of leukemia.
5. Genetic Disorders
Certain inherited conditions dramatically increase leukemia risk. Children with Down syndrome (trisomy 21) are 10-20 times more likely to develop leukemia than children without it. Other predisposing conditions include Li-Fraumeni syndrome, Fanconi anemia, and ataxia-telangiectasia.
6. Family History
Having a first-degree relative with CLL increases your risk of developing CLL by about 2- to 7-fold. However, familial leukemia is relatively uncommon overall. Most patients I see with leukemia have no family history of the disease.
7. Age and Sex
Leukemia risk increases with age for most subtypes. The median age at AML diagnosis is 68 years. Men are diagnosed with leukemia more often than women across nearly all subtypes, though the reasons aren’t fully understood.
Risk Factors by Leukemia Type
| Leukemia Type | Peak Age Group | Key Risk Factors | 5-Year Survival Rate |
|---|---|---|---|
| ALL (Acute Lymphoblastic) | Children (2-5 years) | Down syndrome, radiation, certain genetic syndromes | ~90% (children); ~40% (adults) |
| AML (Acute Myeloid) | Adults (65+) | Benzene, smoking, prior chemotherapy, radiation | ~30% overall |
| CLL (Chronic Lymphocytic) | Adults (70+) | Family history, Agent Orange exposure, male sex | ~87% |
| CML (Chronic Myeloid) | Adults (55-65) | Radiation, Philadelphia chromosome (acquired) | ~70% |
What About Viruses and Infections?
A few infectious agents have direct links to specific leukemia types. Human T-lymphotropic virus type 1 (HTLV-1) causes adult T-cell leukemia/lymphoma, primarily in endemic regions like southern Japan and the Caribbean. The Epstein-Barr virus (EBV) has been associated with certain lymphoid malignancies, though its role in typical leukemia is less direct.
Helicobacter pylori is famously linked to gastric MALT lymphoma but doesn’t cause leukemia. Despite persistent myths online, there’s no evidence that common viral infections like the flu or COVID-19 directly cause leukemia.
Can You Prevent Leukemia?
Honestly, most leukemia cases can’t be prevented because the majority of risk factors are non-modifiable. But you can reduce your risk by:
- Not smoking — this alone cuts AML risk significantly
- Minimizing benzene exposure — use proper protective equipment in industrial settings
- Limiting unnecessary radiation — though diagnostic imaging at standard doses carries negligible risk
- Maintaining awareness if you have a genetic predisposition or prior chemotherapy history
When to See a Doctor
See your doctor promptly if you experience any of these symptoms lasting more than two weeks:
- Persistent fatigue that doesn’t improve with rest
- Unexplained fevers or night sweats
- Easy bruising or bleeding (including bleeding gums or frequent nosebleeds)
- Recurrent infections
- Unintentional weight loss
- Bone pain, especially in the sternum or long bones
- Painless swelling of lymph nodes in the neck, armpits, or groin
A simple complete blood count (CBC) is usually the first step. Abnormal results — particularly a very high or very low white blood cell count, low hemoglobin, or low platelets — will prompt further evaluation, including a bone marrow biopsy if leukemia is suspected.
Frequently Asked Questions
Is leukemia hereditary?
Most leukemia is not inherited. While certain genetic syndromes (Down syndrome, Li-Fraumeni) increase risk, and CLL can cluster in families, the vast majority of leukemia patients have no relevant family history. Having a parent with leukemia does not mean you’ll develop it.
Can stress cause leukemia?
There’s no credible scientific evidence that psychological stress directly causes leukemia. Chronic stress can weaken the immune system, but the leap from weakened immunity to causing DNA mutations in blood cells hasn’t been demonstrated. Don’t let anyone blame you for your diagnosis.
Does leukemia run in children’s families?
Childhood ALL is almost never hereditary. In identical twins, if one develops ALL before age 1, the other twin has a high risk — but this is due to shared blood circulation in the womb, not inherited genes. For most children, leukemia arises from random somatic mutations with no family connection.
Can cell phones or power lines cause leukemia?
Despite decades of investigation, large epidemiological studies have not confirmed a causal link between non-ionizing radiation (from cell phones, power lines, or Wi-Fi) and leukemia. The energy from these sources is too low to damage DNA directly.
What’s the difference between a cause and a risk factor?
A cause directly produces the disease — like how the Philadelphia chromosome drives CML. A risk factor increases your probability of developing the disease but doesn’t guarantee it. Most people exposed to benzene, for instance, never develop leukemia. The distinction matters because leukemia is almost always the result of multiple factors converging, not a single cause.
