What risk means
The World Health Organization estimates that around 38% of cancers could be prevented by avoiding known risk factors and using existing prevention strategies, such as vaccination and screening (WHO cancer fact sheet). That also means most cancers are not explained by anything a person did.
When you read that something "doubles the risk", ask: double of what? A rare cancer that becomes twice as likely may still be rare. Absolute numbers are more useful than percentages.
Modifiable risk factors
These are things that can change. Small changes count, and it is never too late for some benefit.
Tobacco in any form
Smoking, chewing tobacco, betel quid (paan), gutka and bidis are the largest preventable cause of cancer worldwide, including lung, mouth, throat, bladder and many others. Stopping at any age lowers risk, and support doubles the chance of success.
Alcohol
Alcohol is linked to cancers of the mouth, throat, food pipe, liver, bowel and breast. Risk rises with the amount; there is no level known to be risk-free for cancer.
Body weight
Excess body fat is linked to several cancers, including bowel, womb, kidney and breast after menopause. Changes in eating and activity help, alongside support rather than shame.
Physical inactivity
Regular movement is linked to lower risk of bowel, breast and womb cancer. Any activity counts: walking, cycling, housework or dancing.
Diet
Diets high in fibre, fruit, vegetables and whole grains, and lower in processed and red meat, are linked to lower bowel cancer risk.
Ultraviolet (UV) light
Sunburn and sunbeds raise the risk of skin cancer. Shade, clothing and sunscreen help in strong sun.
Non-modifiable risk factors
- Age: most cancers become more common as we get older, because cell changes build up over time. But cancer can happen at any age.
- Sex: some cancers mainly affect people with particular organs, such as cervix, prostate or ovaries.
- Inherited gene changes: a small proportion of cancers are strongly linked to inherited changes such as BRCA1, BRCA2 or Lynch syndrome.
- Previous treatment or conditions: some past treatments and long-term conditions change future risk.
You cannot change these, but knowing about them can change when screening starts or what to watch for.
Family history and genetic risk
Most cancers are not inherited. Inherited gene changes are thought to play a major role in about 5 to 10% of cancers (US National Cancer Institute).
A family history is more likely to be significant when:
- several close relatives on the same side of the family had the same or related cancers (for example breast and ovarian, or bowel and womb)
- a relative had cancer at a young age, for example under 50
- a relative had more than one primary cancer
- a known inherited gene change has been found in the family
In these situations, a clinician may suggest , earlier or extra screening, or other steps. Genetic test results can affect relatives, so counselling before testing is recommended.
Infections linked to cancer
About 10% of cancers diagnosed in 2022 were linked to infections, and in lower-income countries the share is higher (WHO). Many of these are preventable.
| Infection | Linked cancers | Prevention |
|---|---|---|
| Cervical, and some throat, anal, penile, vaginal and vulval cancers | HPV vaccination; cervical screening | |
| Hepatitis B | Liver cancer | Vaccination (including at birth); testing and treatment |
| Hepatitis C | Liver cancer | Testing and curative treatment; safe injections and blood products |
| Helicobacter pylori | Stomach cancer | Testing and treatment when advised |
| HIV | Raises risk of several cancers | Prevention, testing and treatment; more frequent cervical screening |
Environmental and occupational exposure
Some exposures at home or work raise risk. Examples include asbestos, silica dust, diesel exhaust, some industrial chemicals, radon gas, and smoke from cooking with solid fuels indoors.
- Tell a clinician about jobs you have done, even many years ago.
- Ask employers about protective equipment and safety rules.
- Improve ventilation where fuel is burned indoors, where possible.
Air pollution is also a recognised cause of lung cancer. Individual choices only go so far here: this is an area for public policy as much as personal action.
Prevention without blame
No one deserves cancer. People smoke because of addiction and circumstance; weight is shaped by genes, income, stress and environment; exposures at work are often not a choice. Blame helps no one and can stop people seeking care.
Prevention is an invitation, not an accusation.
Questions to take to a clinician
- Does anything in my history, family or work change my risk in a meaningful way?
- Which vaccines or screening tests are right for me?
- Where can I get support to stop tobacco or reduce alcohol?
- Would genetic counselling help me or my family?