What Causes Cancer — and What Can We Actually Control?

The World Health Organization estimates that there are about 20.6 million new cancer cases worldwide each year.

That figure could reach nearly 35 million by 2050.

The number is frightening. Understanding what sits behind it is more useful.

What causes cancer?

Can food change our risk?

Why does movement help?

What happens inside the body when we drink alcohol?

How much control do people have over polluted air, dangerous workplaces and chemicals in the environment?

One question runs through all of these:

When a cancer risk can be prevented, who has the power to prevent it?

WHO and the International Agency for Research on Cancer estimate that up to four in ten cancer cases worldwide could be prevented.

The risks they studied include tobacco, alcohol, excess body weight, low physical activity, air pollution, ultraviolet radiation, infections and dangerous exposures at work.

Some risks sit largely within personal decisions.

Others depend on employers, governments, health services and industries.

That difference matters.

What is cancer?

Our bodies are made of cells.

Cells grow, divide, copy their DNA and eventually die. A complex system controls these processes.

Cancer begins when that control breaks down.

Changed or damaged cells may continue dividing beyond their usual limits. Some survive when the body would normally remove them. Some form tumours. Others spread into different parts of the body.

Many things can contribute to this process:

• ageing;
• inherited genes;
• copying errors when cells divide;
• smoking;
• alcohol;
• infections;
• ultraviolet radiation;
• workplace exposures;
• air pollution;
• diet;
• physical inactivity;
• excess body fat;
• other environmental and biological factors.

Cancer usually develops over time through several interacting processes.

A single meal, a difficult year or one isolated decision rarely explains why one particular person develops the disease.

Risk describes probability.

Someone who reduces every avoidable risk can still develop cancer. Another person may live with several major risks and remain cancer-free.

Both outcomes can happen while the evidence about risk remains true.

A harmful exposure can increase the chance of cancer without deciding one person’s future.

Reducing risk changes the odds. It does not create a guarantee.

Smoking: the clearest risk we can change

Smoking gives us the clearest example of a major avoidable cancer risk.

Tobacco smoke contains thousands of chemicals. WHO says at least 69 are known to cause cancer.

Smoking repeatedly exposes cells to substances that can damage DNA. As this damage accumulates, the chance of dangerous cellular changes rises.

Stopping smoking ends that repeated tobacco exposure, and the risk of several cancers falls over time.

Earlier is better, although stopping at any age can improve health.

The biology only tells part of the story.

Nicotine is addictive. People begin smoking under different circumstances and have very different levels of help available when they try to stop.

Advertising, stress, poverty, social environment and addiction can all shape smoking behaviour.

The tobacco industry also depends on continued sales.

A customer who keeps smoking remains profitable.

A customer who quits disappears from future sales.

That places commercial interests and public health interests in direct conflict.

Personal choice remains part of the picture.

The environment surrounding that choice matters too.

Alcohol: why drinking less helps

Alcohol is linked to several cancers.

The body converts alcohol into a chemical called acetaldehyde.

This substance can damage DNA and proteins.

Alcohol can also contribute to oxidative damage and affect biological processes involved in cancer development.

Lower alcohol intake means lower exposure to these effects.

Cancer risk also reaches beyond alcohol dependence. A person can have an increased risk while remaining far below the level associated with severe addiction.

Here too, biology meets economics.

Public health benefits when harmful alcohol consumption falls.

Alcohol companies make money by selling alcohol.

Business growth usually means reaching more customers, selling more products or encouraging more frequent consumption.

The conflict comes from two different goals.

Public health seeks lower harmful exposure.

The industry seeks higher sales.

Food: patterns matter more than miracle ingredients

Food and cancer attract enormous amounts of poor information.

One week a headline announces that coffee protects us. Another says it harms us.

Social media fills the gap with powders, detox drinks, expensive supplements and restrictive diets.

The useful evidence is quieter.

Long-term eating patterns matter more than individual foods.

Why fibre helps

Foods rich in fibre include:

• beans;
• lentils;
• chickpeas;
• wholegrain bread;
• oats;
• brown rice;
• many fruits;
• many vegetables.

Fibre matters particularly when discussing bowel cancer.

Part of the explanation is physical.

Fibre adds bulk to stools and helps material move through the bowel. Faster movement can reduce the time that potentially harmful substances remain in contact with the bowel lining.

Gut bacteria also ferment some types of fibre and produce short-chain fatty acids.

One of these, called butyrate, appears to support a healthier environment in the colon and influence the way cells grow and behave.

The important point is simple:

Fibre changes what happens inside the bowel, both physically and biologically.

That gives people a real reason to eat it.

Why whole foods help

Vegetables, fruit, beans and whole grains provide fibre, nutrients and a wide range of other compounds.

Scientists continue to study the detailed relationship between specific foods and particular cancers. The broader pattern is already useful.

Current cancer-prevention guidance supports diets built largely around whole grains, vegetables, legumes and fruit, alongside lower consumption of red meat and processed meat.

Health comes from the overall pattern across months and years.

One meal carries very little meaning by itself.

Bodies respond to repeated habits and repeated exposures.

Why processed meat is different

Processed meat includes foods such as bacon, ham, salami and some sausages.

IARC classifies processed meat as carcinogenic to humans because the evidence linking it with colorectal cancer is strong.

This classification tells us that the evidence for causation is convincing. It does not mean that every carcinogen carries the same level of danger.

Smoking carries a far greater cancer risk than eating an occasional bacon sandwich.

The concern around processed meat includes chemicals formed or added during processes such as curing and smoking.

These can include N-nitroso compounds and polycyclic aromatic hydrocarbons. Some high-temperature cooking methods can also produce carcinogenic compounds.

Scientists know that these compounds can be formed, although their exact contribution to the cancer risk linked with meat is still being studied.

The practical lesson concerns repeated exposure.

Eating less processed meat reduces that exposure over time.

Body weight: explain the biology and leave blame behind

Discussions about cancer and body weight often become personal and cruel.

A biological explanation is more useful.

Fat tissue is active tissue.

It affects hormone levels, inflammation, insulin and other growth signals that influence how cells behave.

These systems can change the environment in which some cancers develop and grow.

That helps explain the link between excess body fat and increased risk for several cancers.

Body weight is influenced by a complicated mixture of biological, social and environmental factors, including:

• genetics;
• medication;
• disability and illness;
• sleep;
• stress;
• income;
• working hours;
• access to safe places for movement;
• food prices;
• food availability.

Advice is only useful when people can realistically act on it.

Understanding the biology helps.

So does practical support.

Movement: it changes the body’s internal environment

Physical activity offers benefits even when body weight changes very little.

Movement can affect insulin, hormones, inflammation and immune function.

In the digestive system, activity may also help material pass through the bowel more efficiently.

A gym membership is only one route.

Walking, cycling, swimming, dancing, gardening, physical work and other forms of movement all contribute.

The useful aim is regular movement that fits a person’s body and circumstances.

Living systems respond to movement.

That is the reason behind the advice.

Sunlight: why burning matters

Ultraviolet radiation can damage DNA in skin cells.

The body reacts to UV exposure in several ways. Tanning is one of those responses.

A tan shows that the skin has reacted to ultraviolet radiation.

Repeated high exposure and sunburn increase the amount of DNA damage skin cells experience.

Reducing excessive UV exposure lowers that repeated damage.

Useful actions include:

• avoiding sunbeds;
• reducing repeated sunburn;
• using shade;
• wearing protective clothing;
• using suitable sunscreen.

Ordinary outdoor life still matters for movement, wellbeing and daily life.

The aim is sensible protection from excessive UV exposure.

Vaccines can prevent some cancers

Vaccination is usually associated with preventing infectious disease.

Some vaccines also prevent cancers.

Certain infections can begin biological processes that lead to cancer years later.

Two important examples are HPV and hepatitis B.

Certain types of HPV can cause cancers of the cervix and several other parts of the body.

HPV vaccines protect against dangerous types of the virus before infection begins the long chain of cellular changes that may eventually lead to cancer.

Hepatitis B can cause long-term infection and inflammation in the liver.

Over many years, that damage can increase the chance of liver cancer.

Vaccination prevents the infection that starts this process.

The science is clear.

Access is a political question.

Children depend on national vaccination programmes.

Families depend on healthcare systems, supply chains and public funding.

Cancer prevention therefore happens at both personal and collective levels.

A cancer risk may be preventable even when the individual exposed to it holds very little power to prevent it.

Air pollution: a risk controlled mainly by society

Air pollution shows the limits of individual advice.

Fine particles and carcinogenic chemicals can travel deep into the lungs.

Long-term exposure can contribute to inflammation and cellular damage and increases the risk of lung cancer.

An individual may make small changes to reduce exposure.

Large reductions require decisions about:

• transport;
• energy;
• industry;
• housing;
• urban planning;
• emissions;
• regulation.

Air pollution appears among the cancer risks identified in WHO and IARC prevention work.

The same research also examines occupational exposures: risks people face because of the work they do.

This reveals an important weakness in the word preventable.

Some risks can be reduced mainly through collective decisions.

For the person breathing polluted air, personal control may be very small.

Dangerous work: who controls the exposure?

Some jobs expose people to substances and conditions that increase cancer risk.

The danger depends on the material, the amount of exposure, the duration and the quality of protection.

Workers often have limited control over the main decisions.

Employers may decide:

• which materials are used;
• how ventilation is designed;
• whether safer alternatives are purchased;
• which protective equipment is supplied;
• how safety procedures are enforced;
• how complaints are handled.

Personal protective equipment can reduce exposure.

Removing a hazard, replacing a dangerous substance and improving ventilation can provide stronger protection.

Workplace cancer prevention therefore depends heavily on regulation, enforcement and employer behaviour.

Responsibility should follow control.

The risks built into being alive

Some cancer risks come from biology itself.

Age

Cancer risk rises with age.

Cells have had more time to divide, experience damage and accumulate changes.

The world’s population is also growing and ageing. This forms part of the reason total cancer cases are projected to rise sharply by 2050.

Longer lives bring many benefits.

They also give age-related diseases more time to develop.

The genes we are born with

Some people inherit genetic changes that increase their risk of particular cancers.

Testing can sometimes identify these variants.

Medical monitoring, screening and preventive treatment may then help manage the risk.

The inherited change comes from biology.

Healthcare can influence what happens next.

Chance

Every time a cell divides, it copies DNA.

The body has remarkable repair systems, yet biological copying remains an imperfect process.

Some cancer-related changes arise through ordinary cellular activity without a clear avoidable cause.

People often want a clean explanation and a clear rule that guarantees safety.

Biology offers probabilities instead.

Every useful reduction in risk changes the odds.

That is valuable, even when certainty remains impossible.

What happens when harmful exposure is profitable?

Some cancer risks sit inside industries that make money from continued exposure.

WHO uses the term commercial determinants of health to describe the ways company behaviour, products, marketing and business decisions influence health.

Its work includes industries such as tobacco, alcohol, ultra-processed food and fossil fuels.

The tobacco example is the clearest.

Public health improves when fewer people smoke.

Tobacco companies earn money through continued tobacco sales.

Each person who quits gains health and removes future purchases from the market.

The conflict comes directly from the business model.

Alcohol creates a similar tension.

Health improves when harmful consumption falls.

Business growth comes from greater sales.

Food systems create another version of the problem.

People may understand that beans, vegetables, whole grains and fruit are useful, while still living in environments where heavily marketed convenience food can be cheaper, easier to find or quicker to prepare.

A tired person finishing a long shift makes choices inside a system of prices, working hours, transport and availability.

Those choices remain real.

So do the forces shaping them.

Pollution raises the same issue.

A company receives the financial benefit from production.

The surrounding population may carry part of the health cost through polluted air.

Safer technology, stronger controls and cleaner production often cost money.

Companies therefore have a financial incentive to keep those costs low.

Government regulation exists partly because markets give businesses limited reason to pay voluntarily for benefits enjoyed by the wider public.

Workplace safety follows the same pattern.

Better ventilation costs money.

Safer chemicals may cost money.

Protective equipment costs money.

Thorough monitoring and enforcement cost money.

For the worker, these measures protect health.

On a company balance sheet, they appear as costs.

The problem is larger than a few bad companies.

It comes from systems that reward profit while allowing health costs to fall elsewhere.

Personal choice happens inside a designed environment

Health advice often imagines a person standing alone in front of a set of free choices.

Real life looks different.

Prices matter.

Advertising matters.

Poverty matters.

Working hours matter.

Housing matters.

Transport matters.

Regulation matters.

Availability matters.

A child grows up inside an advertising system created by adults and companies.

A low-paid worker buys food within the limits of their income, time and local shops.

A renter has limited power over the building they live in.

A resident beside a busy road lives with planning decisions made long before they arrived.

An employee works with materials selected by someone higher in the organisation.

Personal behaviour remains important.

Power is distributed unevenly.

A serious cancer-prevention strategy has to understand both.

What can a person actually do?

Cancer risk can be reduced in several practical ways.

Avoid smoking. Use support to stop when needed.

Reduce alcohol intake. Lower exposure means lower risk.

Eat more fibre-rich food. Beans, lentils, whole grains, vegetables and fruit all help.

Reduce processed meat. The concern is repeated exposure over time.

Move regularly. Choose forms of movement that suit your body and daily life.

Protect your skin. Reduce excessive ultraviolet exposure and avoid sunbeds.

Use appropriate vaccines. Some vaccines prevent infections that can later cause cancer.

Take workplace safety seriously. Raise concerns through safe channels where possible.

Respond to screening invitations. Take part in programmes that apply to you.

Get persistent or unusual changes checked. Early investigation can matter.

Each action changes part of the risk picture.

Together, they can make a meaningful difference.

Cancer prevention is bigger than self-improvement

Cancer advice often comes down to a familiar list:

Eat better.

Move more.

Drink less.

Stop smoking.

These actions matter.

They form one part of the story.

Genes shape risk.

Age shapes risk.

Cell biology shapes risk.

The air around homes shapes risk.

Conditions at work shape risk.

Food prices and availability shape behaviour.

Vaccination programmes shape infection-related cancer risk.

Health services shape whether suspicious symptoms are investigated quickly.

Governments, industries, employers, communities and individuals all hold different parts of the power.

The question therefore has two parts.

What can I do to reduce my own risk of cancer?

And:

Which cancer risks could we reduce together, who has the power to reduce them, and what stands in the way?

Cancer prevention is partly personal.

It is also political.

We should be honest about which part belongs to which.