Causes and risk factors

There are things that can increase your risk of getting cancer. Find out what these might be and the possible changes you could make to reduce your risk.

What are risk factors?

Most of the time, we do not know why one person gets cancer while someone else does not.

Some things can increase a person’s risk of getting cancer. These are called risk factors. There are some general risk factors for developing cancer. And there are some that increase the risk of developing a specific type of cancer.

Having 1 or more risk factors does not mean you will definitely get cancer. Some factors only increase your risk a small amount. Others are much more likely to cause cancer, such as smoking. You can still develop cancer even if you do not have any known risk factors.

About 4 in 10 cancers (40%) could be prevented. Living a healthier lifestyle can help reduce your risk (see below). But you cannot reduce your risk of cancer completely.

General risk factors

General risk factors for cancer include the following:

  • Age – the risk of developing cancer increases as you get older.
  • Lifestyle factors – these include smoking, your weight, your diet, how active you are, sun exposure and sunbed use, and how much alcohol you drink. You can read more about how to reduce your risk below.
  • Family history – some cancers are more common in some families. We have more information for people with a family history of cancer.

Lifestyle risk factors and reducing your risk

There are many factors involved in developing cancer. Having a healthy lifestyle does not guarantee that you will not get cancer. But it reduces your risk and improves your general health. It also reduces your risk of other illnesses such as heart disease.

Giving up smoking

Smoking is the biggest cause of cancer in the UK. It causes 15 in every 100 cancers (15%). Over 70 in 100 lung cancers (72%) are caused by smoking. Giving up smoking is the single most important thing you can do for your health.

Chewing or sucking tobacco is not a safe alternative to smoking cigarettes. If you chew or suck tobacco, you have a higher risk of mouth and oral cancers.

Breathing in other people’s tobacco smoke (passive smoking) also increases your risk of cancer. Keeping your home smoke-free will protect you and your family’s health.

Many people now use e-cigarettes. The long-term effects of e-cigarettes are not yet fully known. E-cigarettes are thought to be a lot safer than tobacco cigarettes. But it is still much better to not smoke at all.

If you want to give up smoking, it is never too late to stop. Ask your GP for advice, or contact a stop-smoking service in your area.

Keep to a healthy weight

After smoking, being overweight is the second biggest cause of cancer. It increases the risk of many cancer types, including cancers of the bowel, kidney, womb, and gullet (oesophagus). Women who are overweight and have had the menopause also have a higher risk of breast cancer.

Keeping to a healthy weight reduces your risk of cancer and other health problems, such as heart disease and diabetes.

Here are some tips to help you keep to a healthy weight:

  • Eat a healthy diet with lots of fruit and vegetables and less fat and sugar.
  • Only eat as much food as you need depending on how active you are.
  • Be more physically active.

If you are worried about your weight or need more information, talk to your GP or a dietitian.

Eat a healthy diet

There is no single food that causes or prevents cancer. Eating a balanced diet is good for your overall health and helps reduce your risk of some cancers. It can also help you keep to a healthy weight.

Try to limit how much red and processed meat you eat. These are linked to a higher risk of bowel and prostate cancer. Red meat is beef, pork, lamb and veal. Processed meats include sausages, bacon, salami, tinned meats, and packet meats such as the ham you have in sandwiches. We have more information about eating a balanced diet.

You can find more detailed information about diet and cancer risk on the World Cancer Research Fund website.

Be physically active

Regular physical activity can help reduce the risk of some cancers. Physical activity is also good for your general health and well-being. Each week, you should try to do at least 150 minutes of moderate activity or 75 minutes of vigorous activity.

Moderate activity raises your heartbeat and makes your breathing faster. It includes things like brisk walking, riding a bike and dancing.

Vigorous activity makes you breathe hard and not be able to say much without taking a breath. It includes running, swimming and walking up the stairs.

If you are not used to doing exercise, ask your GP for advice about getting started. You can find more information about keeping active on the following websites:

Limit how much alcohol you drink

Drinking alcohol increases your risk of mouth and throat cancers. It is also linked to cancers of the gullet (oesophagus), bowel, liver and breast.

In general, the more you drink, the higher your risk. Your risk is higher if you also smoke.

Current guidelines say:

  • do not drink more than 14 units of alcohol in a week
  • spread the amount you drink in 1 week over 3 or more days
  • try to have several alcohol-free days every week.

There is no safe level of drinking alcohol. But sticking to these guidelines reduces your risk of damaging your health.

You can find more information about alcohol and drinking guidelines at

Take care in the sun

Spending some time outside helps you stay healthy. Our bodies need sunlight to make vitamin D. This is important for bone health and reduces the risk of some illnesses.

But it is important to protect your skin from too much sun. This is because too much sun can increase your risk of skin cancer. If you have white or pale skin or do not tan easily, you should avoid letting your skin go pink or red in the sun. If you have black or brown skin, the signs of sun damage may not be as obvious, but you should still protect your skin in the sun.

Here are some tips to help you stay safe in the sun:

  • Wear clothes made of fabric that does not let sunlight through. Make sure they cover your body, arms and legs.
  • Wear a wide-brimmed hat that protects your face, ears and neck.
  • Wear sunglasses with wide wraparound lenses or wide arms with the CE Mark and British Standard Mark 12312-1:2013 E.
  • Stay in the shade when you can, especially between 11am and 3pm.
  • Use a suncream with a sun protection factor (SPF) of at least 30. Choose one that protects against UVA and UVB, with four or five stars.

Using sunbeds or sunlamps also increases your risk of skin cancer. If you want to look tanned, use fake tan lotions or sprays.

Viruses and risk of cancer

A small number of viruses have been linked to a higher risk of certain types of cancer. These viruses include:

There is a vaccine to protect against HPV. This is given to children aged 12 to 13 as part of the NHS vaccination programme.

If you have an increased risk of cancer caused by HPV, you may be able to have an HPV vaccine. Your GP, local sexual health clinic or HIV clinic can give you more information.

Using condoms and dental dams during sex can help protect you from some viruses.

If you inject drugs, it is important to never share needles. This is because viruses can pass from person to person in the blood.

Other risk factors

Workplace and environmental factors

 There are certain things we may be exposed to in the environment or at work that can increase the risk of getting cancer. 

Substances that cause cancer are called carcinogens. The risk from carcinogens can vary. It might depend on how much of the substance you were exposed to, and for how long. 

Sometimes it takes years for cancer to develop. People are still getting cancer because of a job they did a long time ago, before we had better health-and-safety laws.

Some people can claim Industrial Injuries Disablement Benefit (IIDB) if something they were exposed to at work caused them to get cancer. We have more information about benefits and financial support when you have cancer.


Asbestos is a natural mineral that is now banned in the UK. It can damage the lungs and cause mesothelioma and lung cancer

The people most likely to have been exposed to asbestos are those who have worked in construction, shipbuilding or boiler making. But people who have not worked with asbestos can also be at risk. They might have been exposed to asbestos factories or buildings containing asbestos. Or they may have lived with someone working with asbestos.

Industrial chemicals

Some chemicals have been linked to bladder cancer and upper urinary tract urothelial cancer (UTUC). These chemicals were used in dye factories and other industries. Many of them are now banned. But cancer can take more than 25 years to develop after exposure to the chemicals.

Some chemicals can increase the risk of skin cancer. Many of these chemicals are also banned.

Ultraviolet (UV) radiation

One of the main environmental causes of cancer is ultraviolet (UV) radiation from the sun. Many skin cancers, including melanoma, are caused by spending too much time in the sun. Some people have a higher risk of skin cancer – for example, those who work outdoors. There are things you can do to reduce your risk.


Radon is another source of radiation that may be linked to cancer. Radon is a natural gas found in rock in parts of the UK. It has been linked to lung cancer. But the risk is very small.

Air pollution

Air pollution is caused by particles in the air which come from things such as fumes from vehicles and factories. Air pollution can increase the risk of lung cancer. But the risk is low. Air pollution levels in the UK are low compared to other countries.

Low immunity

Low immunity means your immune system does not work as well as it should. This could be because of a medical condition such as HIV. It can also be the result of treatments or medicines used to treat cancer. Having low immunity means you are more likely to get infections.

If you have low immunity, you may be more likely to develop some cancers. These cancers include:

Pre-cancerous and genetic conditions

An inherited genetic condition is a genetic change passed from a parent to their child. It is passed when a sperm and an egg join to start making a baby (conception). Some genetic conditions can increase a person’s risk of getting cancer in their lifetime.

A pre-cancerous condition is when cells are found to have abnormal changes that may lead to cancer if left untreated.

Having a pre-cancerous or inherited genetic condition does not mean you have cancer. Nor does it mean you will definitely get cancer. But it can increase your risk of developing it. If you have a pre-cancerous or inherited genetic condition, you may need to:

  • have regular checks with a doctor or genetics specialist
  • have treatment to help prevent cancer in the future.
Related pages

About our information

  • Reviewers

    This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by members of Macmillan’s Centre of Clinical Expertise.

    Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information.

The language we use

We want everyone affected by cancer to feel our information is written for them.

We want our information to be as clear as possible. To do this, we try to:

  • use plain English
  • explain medical words
  • use short sentences
  • use illustrations to explain text
  • structure the information clearly
  • make sure important points are clear.

We use gender-inclusive language and talk to our readers as ‘you’ so that everyone feels included. Where clinically necessary we use the terms ‘men’ and ‘women’ or ‘male’ and ‘female’. For example, we do so when talking about parts of the body or mentioning statistics or research about who is affected.

You can read more about how we produce our information here.

Date reviewed

Reviewed: 01 October 2022
Next review: 01 October 2025
Trusted Information Creator - Patient Information Forum
Trusted Information Creator - Patient Information Forum

Our cancer information meets the PIF TICK quality mark.

This means it is easy to use, up-to-date and based on the latest evidence. Learn more about how we produce our information.