Understanding what may increase the risk of cancer can help us make informed choices about prevention, screening and healthcare.
Cancer develops through changes that affect how cells grow, divide and survive. These changes can arise for different reasons. Some are related to inherited genetic factors, while others develop during a person’s lifetime because of natural errors in cell division or exposure to certain environmental, lifestyle or biological factors.
Importantly, having a risk factor does not mean that a person will definitely develop cancer. Likewise, people can develop cancer even when they do not have an obvious risk factor. In many individual cases, it is not possible to identify one specific cause.
Understanding risk factors is therefore not about assigning blame. It is about recognizing what can potentially be changed, what cannot, and where prevention and early detection can make a difference.
What Causes Cancer?
Cancer is fundamentally a disease involving changes to genes that control how cells function, particularly how they grow and divide.
Genetic changes associated with cancer can occur in several ways:
- They may occur as random errors when cells divide.
- DNA can be damaged by certain environmental exposures.
- Some cancer-associated genetic changes can be inherited from a parent.
- Certain infections can contribute to genetic or cellular changes associated with cancer.
Over time, multiple genetic changes can accumulate within cells. When these changes interfere with the normal controls that regulate cell growth and survival, a normal cell may eventually become cancerous.
This is one reason cancer is considered a complex and multifactorial disease rather than something that usually has a single cause.
What Is a Cancer Risk Factor?
A risk factor is something that increases a person’s chance of developing a particular disease.
For cancer, risk factors can include characteristics that cannot be changed—such as age or inherited genetic changes—as well as exposures and behaviours that may be modified.
The National Cancer Institute identifies several established or studied cancer risk factors, including age, alcohol, tobacco, obesity, diet, chronic inflammation, hormones, immunosuppression, infectious agents, radiation, sunlight and exposure to cancer-causing substances.
Risk factors also vary according to the type of cancer. A factor associated with one cancer may not have the same relevance to another.
Major Cancer Risk Factors
1. Tobacco and Smoking
Tobacco is one of the most important preventable causes of cancer.
Smoking and other forms of tobacco exposure can damage DNA and increase the risk of multiple cancers. Tobacco is associated with cancers of the lung, mouth, throat, larynx, oesophagus, bladder, kidney, liver, stomach, pancreas, colon and rectum, cervix, as well as certain blood cancers.
Smokeless tobacco is also harmful and is associated with cancers including those of the mouth, oesophagus and pancreas.
Second-hand smoke can also expose non-smokers to cancer-causing substances.
There is no safe level of tobacco use. Stopping tobacco use is one of the most important steps a person can take to reduce their cancer risk.
Tobacco and cancer prevention
For people who use tobacco, quitting can reduce cancer risk. The benefits of stopping tobacco use extend beyond cancer and can also improve cardiovascular and respiratory health.
For patients already diagnosed with cancer, stopping tobacco remains important and may improve overall health and treatment outcomes.
2. Alcohol Consumption
Alcohol consumption is associated with an increased risk of several cancers.
Alcohol is linked with cancers including those of the mouth, pharynx, larynx, oesophagus, liver, colorectum and breast.
The relationship between alcohol and cancer risk is influenced by the amount consumed, and alcohol can contribute to cancer through several biological mechanisms, including effects that can damage DNA and alter cellular processes.
The combination of alcohol and tobacco is particularly important. Research has shown that people who use both can have substantially greater risks of certain cancers of the upper aerodigestive tract than people exposed to either factor alone.
Reducing or avoiding alcohol can therefore be an important component of cancer-risk reduction.
3. Excess Body Weight and Obesity
Body weight is another factor associated with cancer risk.
Overweight and obesity have been linked with several cancers, including cancers of the oesophagus, colorectum, breast, endometrium and kidney.
The relationship between excess body weight and cancer is complex and can involve hormonal, metabolic and inflammatory processes.
Maintaining a healthy body weight, together with regular physical activity and a balanced diet, can contribute to overall health and may reduce the risk of several cancers.
It is important, however, to approach weight and cancer prevention without oversimplification. Body weight is only one factor among many, and cancer can occur in people across a wide range of body weights.
4. Diet and Nutrition
Diet can influence cancer risk, although no single food or dietary habit can completely prevent cancer.
A healthy dietary pattern generally emphasizes a variety of fruits, vegetables and other nutrient-rich foods, while limiting excessive consumption of highly processed foods and certain foods associated with increased cancer risk.
WHO identifies unhealthy diet among the important modifiable risk factors for cancer and recommends a healthy diet including fruits and vegetables.
Diet should be considered as part of an overall lifestyle rather than as a standalone cancer-prevention strategy.
There is also an important distinction between healthy eating and unproven “anti-cancer” diets. No particular food, juice, supplement or restrictive diet should be presented as a substitute for evidence-based cancer prevention, screening or medical treatment.
5. Physical Inactivity
Regular physical activity contributes to overall health and is associated with a lower risk of several chronic diseases, including some cancers.
Physical inactivity can also contribute to excess body weight and metabolic health problems, which may further influence cancer risk.
WHO identifies physical inactivity as a cancer risk factor and recommends regular physical activity as part of cancer prevention.
Being physically active does not mean that a person needs to follow an intense exercise programme. The appropriate level and type of activity depend on age, health status, fitness and individual circumstances.
For people living with cancer, exercise recommendations should also take into account the diagnosis, treatment and overall physical condition.
6. Age
Age is one of the most important risk factors for cancer.
As we grow older, cells accumulate genetic changes over time. At the same time, the body’s ability to repair or eliminate cells with certain types of DNA damage can become less effective. This contributes to the increasing incidence of many cancers with age.
Age, of course, cannot be changed.
This makes appropriate screening, awareness and timely evaluation of concerning symptoms particularly important as people get older.
7. Family History and Inherited Genetic Risk
Cancer itself is not generally inherited from parents to children. However, a genetic change that increases the risk of developing cancer can sometimes be inherited.
For example, inherited changes in genes such as BRCA1 and BRCA2 can substantially increase the risk of certain cancers.
A family history of cancer does not automatically mean that a person has an inherited cancer syndrome.
However, certain patterns may warrant further evaluation—for example:
- Multiple close relatives with related cancers
- Cancer occurring at unusually young ages
- Several generations affected by certain cancers
- Multiple primary cancers in the same individual
- Certain combinations of cancers within a family
When appropriate, a healthcare professional may recommend genetic counselling or genetic testing based on the patient’s personal and family history.
The important message is that inherited cancer risk is not the same as a cancer diagnosis. Having an inherited risk-associated genetic change increases risk but does not mean that cancer will definitely develop.
8. Cancer-Causing Infections
Some infections can increase the risk of developing certain cancers.
WHO identifies several important cancer-associated infections, including:
- Human papillomavirus (HPV)
- Hepatitis B virus (HBV)
- Hepatitis C virus (HCV)
- Helicobacter pylori (H. pylori)
- Epstein-Barr virus (EBV)
These infections can contribute to cancer through different biological mechanisms.
For example, persistent infection with certain types of HPV is strongly associated with cervical cancer and also contributes to several other cancers.
Chronic hepatitis B and hepatitis C infections can increase the risk of liver cancer.
Some infection-related cancers can potentially be prevented through vaccination, appropriate infection prevention and treatment of certain chronic infections.
HPV and hepatitis B vaccination are important examples of cancer-prevention strategies where vaccination is recommended for appropriate groups.
9. Radiation Exposure
Radiation is another category of cancer risk factor.
Two important forms are:
Ionizing radiation
Ionizing radiation has enough energy to damage DNA. Sources can include certain medical exposures and environmental or occupational sources.
Medical radiation can be extremely valuable for diagnosing and treating disease, and necessary radiation-based medical procedures should not be avoided simply because radiation can carry risks.
Instead, medical radiation should be used appropriately and safely, with the benefits and risks considered by qualified healthcare professionals.
Ultraviolet radiation
Ultraviolet (UV) radiation from sunlight and artificial tanning devices can damage skin-cell DNA and is a major risk factor for skin cancers.
Reducing excessive UV exposure and using appropriate sun-protection measures can help reduce this risk.
10. Occupational and Environmental Exposures
Some people may encounter cancer-causing substances through their workplace or environment.
Occupational exposures can include certain chemicals, dusts, fibres and other substances, depending on the industry and working conditions.
WHO identifies occupational carcinogens as being associated with cancers including lung cancer, mesothelioma and bladder cancer.
Environmental exposures can also include air pollution and other contaminants.
Not every environmental exposure causes cancer, and the level, duration and nature of exposure matter. Where a known occupational or environmental hazard exists, appropriate workplace safety measures and exposure controls are important.
11. Chronic Inflammation and Certain Medical Conditions
Long-term inflammation can contribute to changes in the cellular environment and is associated with an increased risk of some cancers.
Certain chronic diseases and conditions can therefore be associated with cancer risk.
This does not mean that every person with a chronic inflammatory condition will develop cancer.
The relationship depends on the specific disease, its duration, severity and other individual factors.
People with certain chronic medical conditions may benefit from appropriate medical follow-up and screening based on their individual risk.
12. Hormonal and Reproductive Factors
Hormones can influence the growth of certain tissues, and hormonal factors can therefore affect the risk of some cancers.
The relationship between hormones and cancer is complex and can depend on factors such as age, reproductive history, endogenous hormone exposure and certain medications or hormone-based treatments.
Hormonal factors should therefore be considered in the context of an individual’s complete medical history rather than interpreted as an isolated cause of cancer.
13. Weakened Immune System
A weakened immune system can affect the body’s ability to control abnormal cells and certain infections.
People whose immune systems are suppressed—for example, because of certain medicines or medical conditions—may have an increased risk of particular cancers.
This is one reason cancer risk assessment needs to consider a person’s complete medical history rather than focusing only on lifestyle factors.
Can Cancer Be Prevented?
Not all cancers can be prevented.
Some risk factors cannot be changed, including age and certain inherited genetic changes. Other cancers arise through genetic changes that occur during normal cell division and accumulate over time.
However, a significant proportion of cancers are associated with potentially preventable causes.
A 2026 WHO/IARC analysis estimated that 37% of new cancer cases globally in 2022—around 7.1 million cases—were linked to preventable causes, including tobacco, infections, alcohol, high body mass index, physical inactivity, air pollution and ultraviolet radiation.
This highlights the importance of prevention, while also reminding us that prevention cannot eliminate cancer completely.
Practical Steps to Reduce Cancer Risk
There is no guaranteed way to prevent cancer, but several evidence-based measures can reduce the risk of developing certain cancers.
Avoid tobacco
Do not smoke or use tobacco products. Avoiding second-hand smoke is also important. If you use tobacco, seek appropriate support to quit.
Limit or avoid alcohol
Reducing alcohol consumption can reduce alcohol-associated cancer risk.
Maintain a healthy body weight
Aim for a healthy weight through sustainable eating habits and regular physical activity.
Stay physically active
Regular physical activity is beneficial for overall health and can contribute to cancer-risk reduction.
Eat a balanced diet
Choose a varied diet with adequate fruits and vegetables and limit excessive consumption of foods associated with poorer health outcomes.
Protect yourself from excessive UV exposure
Use appropriate sun protection and avoid unnecessary exposure to intense UV radiation and artificial tanning devices.
Follow recommended vaccinations
Vaccination against HPV and hepatitis B, when recommended for an individual, can help prevent infections associated with certain cancers.
Follow appropriate screening recommendations
Screening can help detect certain cancers or precancerous changes before symptoms develop. The appropriate screening programme depends on factors such as age, sex, personal history and individual risk.
Risk Factors Do Not Tell the Whole Story
One of the most important things to understand about cancer risk is that risk is not destiny.
A person may have several risk factors and never develop cancer. Another person may develop cancer without having any obvious or recognized risk factor.
Cancer usually results from a complex interaction of genetic, biological, environmental and lifestyle factors, and in many individual cases the exact reason cancer developed cannot be determined.
For this reason, cancer prevention should not become a source of guilt or blame.
The goal is to focus on what can reasonably be changed while also recognizing the factors that cannot.
When Should You Talk to a Doctor?
Risk factors are only one part of cancer care.
If you notice a persistent or unusual change in your health, it is important to discuss it with an appropriate healthcare professional rather than trying to determine the cause yourself.
Depending on the situation, symptoms or findings may require examination, imaging, laboratory tests, screening or other investigations.
A symptom does not automatically mean cancer. Many symptoms have non-cancerous causes. However, persistent or unexplained changes deserve appropriate medical evaluation.
Understanding Your Individual Risk
There is no single “cancer risk test” that can accurately predict whether every person will develop cancer.
A meaningful risk assessment may require consideration of:
- Age
- Personal medical history
- Family history
- Tobacco and alcohol exposure
- Lifestyle factors
- Previous cancer or precancerous conditions
- Certain infections
- Occupational or environmental exposures
- Previous radiation exposure
- Genetic factors
If a person has a strong personal or family history of cancer, discussing this history with a doctor can help determine whether additional screening, genetic counselling or other evaluation may be appropriate.
Prevention, Awareness and Early Detection
Cancer prevention and early detection are closely connected.
Reducing avoidable risk factors can lower the likelihood of developing some cancers. At the same time, appropriate screening and timely medical evaluation can help detect certain cancers earlier, when treatment may be more effective.
WHO notes that the cancer burden can be reduced through prevention, early detection and appropriate treatment and care.
This is why cancer awareness should go beyond knowing the word “cancer.”
It should include understanding risk factors, recognizing concerning changes, following appropriate screening recommendations and seeking medical advice when necessary.
A Message From Dr. Geeta Singh
Cancer is a complex disease, and there is rarely one single reason why it develops. Some risk factors are within our control, while others are not. What we can do is understand our individual risk, make evidence-based choices, follow appropriate screening recommendations and seek medical advice when something changes.
Cancer awareness should not create fear. It should create knowledge—and knowledge can help us make better decisions about our health.
