Can ionising radiation cause cancer?

What is ionising radiation?

Radiation is how energy, such as light or heat, moves around. Ionising radiation is high-energy radiation. 

We are exposed to small amounts of ionising radiation every day. It can come from natural sources such as the air, soil and water. The main source in the UK is radon gas from the ground.  

There are also artificial sources of ionising radiation such as x-rays. 

Mobile phones, microwaves and radios do not use ionising radiation. These use radio waves, which are a weak form of radiation that doesn’t cause cancer. You can find out more about radiofrequency radiation on our mobile phones page. 

How can ionising radiation cause cancer?

Ionising radiation can cause cancer if a person is exposed to a lot of it.  This is because it can damage our DNA, which can lead to cancer. 

The level of ionising radiation most people are exposed to every day is very low, so the risk of developing cancer from this exposure is low.  

Around 2 in 100 cancer cases in the UK (2015) are linked to ionising radiation. This includes radon-related lung cancers, many of which could be prevented by not smoking.  

Find out more about the link between radon, smoking and cancer.  

The UK government regulates the use of ionising radiation to help reduce potential negative health effects. 

Can X-rays, CT scans and MRI scans cause cancer? 

Ionising radiation from medical imaging slightly increases the risk of cancer. But the amount of radiation used is small and the risk is low. 

Medical x-rays and scans are very important for diagnosing illnesses and conditions. The benefit of correctly diagnosing and treating health conditions outweighs any potential harm from the radiation. 

The UK government sets guidelines on using ionising radiation in medical scans to make them as safe as possible. The guidelines state that medical scans are only done when needed and use the smallest dose of radiation possible to get the imaging result. 

Even for scans that use higher doses of ionising radiation, the risk of cancer is still low and is outweighed by the importance of getting the right diagnosis and treatment.  

Types of medical scans that use ionising radiation include: 

• x-rays  
• CT scans 
• mammography (used for breast screening) 
• fluoroscopy (e.g. barium x-rays to look at the digestive system). 
• nuclear medicine imaging 

Different types of medical scans use different amounts of radiation. For example x-rays usually use less radiation than CT scans. 

There are also types of medical imaging that don’t use ionising radiation, including ultrasounds and magnetic resonance imaging (MRI) scans. 

These types of scans do not increase the risk of cancer. 

What should I do if I am worried about having a medical scan?  

Talk to your doctor if you’re worried about having a medical scan. You can ask for reassurance that the scan is needed and how it will help to diagnose you.  

The risks from medical scans depend on many factors, including:  

• your age 
• the type of scan used 
• the body part being scanned 
• if you have had any scans before 

Your doctor might talk to you about these things, as they want to make sure the potential benefits of the scan outweigh the risks for you.  

You should tell your doctor about any previous scans you have had. 

Also tell your doctor if you may be pregnant or are breastfeeding. This is because unborn babies and babies are at higher risk from radiation. 

We have information on radiation used in cancer treatment on our page on radiotherapy.  

Can radiation from flying cause cancer? 

Air travel is unlikely to increase your risk of cancer. 

Cosmic radiation from space is another type of natural ionising radiation. The earth's atmosphere shields us from most cosmic radiation. But the atmosphere is thinner higher up, so this means someone flying in a plane meets more cosmic radiation than someone on the ground. 

This small amount of extra cosmic radiation from flying is unlikely to increase the risk of cancer. 

Some people are also worried about radiation from airport scanners, when people are scanned through security before travelling by plane. Not all body scans at airports use ionising radiation. For example, in the UK all airport scanners use non-ionising radiation. 

Airport body scanners that do use ionising radiation use a very small amount. There is no reliable evidence that this increases the risk of cancer.