Radiation is a general term referring to any sort of energy that can travel through space either as a wave or a particle.
Everyone is exposed to background radiation from natural sources such as soil, rocks and stones. Even water and certain foods, including nuts, bananas and potatoes, contain small traces of radiation.
However, as background radiation occurs in low levels, it's very unlikely to cause health problems.
Types of radiation
There are two types of radiation that may be associated with health risks. These are:
non-ionising radiation (low energy)
ionising radiation (high energy)
You'll usually only be exposed to man-made ionising radiation during certain medical tests, but the levels are so low that the chances of problems developing are small.
Examples of non-ionising radiation include:
radio and radar waves
wireless internet connections (wifi)
mobile phone signals
Overall, there's little evidence to suggest most types of non-ionising radiation are harmful at levels you're normally exposed to, but some forms of non-ionising radiation are potentially dangerous.
The main proven danger of non-ionising radiation is damage to the skin caused by ultraviolet (UV) light. UV light primarily comes from the sun, but is also produced by sunbeds and sunlamps.
Low levels of exposure to UV light are actually beneficial to health – sunlight helps our bodies produce vitamin D, which is important as it helps keeps bones strong and healthy.
However, high levels of exposure to UV light can be harmful as it can cause sunburn, as well as increasing your risk of developing melanoma and non-melanoma skin cancer.
Some people have also argued telecommunications devices that use non-ionising radiation, such as mobile phones or wifi, could be potentially dangerous.
But as yet, a number of British and international studies haven't identified any health risks associated with these devices.
A research programme known as the Mobile Telecommunications and Health Research (MTHR) Programme is ongoing in the UK. Their reports in 2007 and 2012 concluded there's no evidence that short-term use of mobile phones increases the risk of cancer, or affects the normal functioning of the brain.
This has been supported by further studies, which also show no link between mobile phones and problems such as cancer.
However, as evidence is only based on mobile phone use over the last 20 years, there's still some uncertainty about possible long-term risks or associated problems.
Ionising radiation in medical tests and treatments
Ionising radiation is a more powerful form of radiation than non-ionising radiation, and is more likely to cause damage to cells. Exposure to ionising radiation can increase the risk of cancer. High doses can cause serious damage, including radiation burns.
One of the most common sources of exposure to man-made ionising radiation is during medical tests or treatments.
However, while it may sound dangerous, the radiation used in medicine is closely controlled, and the risk of any problems resulting from exposure to radiation is very small.
Examples of using ionising radiation to treat or diagnose a condition include:
tests such as X-rays and CT scans – a low level of ionising radiation is used to produce images of the inside of the body
nuclear medicine – for example, a mild radioactive substance can be injected into the bloodstream so it shows up better on an imaging scan
radiotherapy – a common cancer treatment that uses ionising radiation to kill cancerous cells
Measuring radiation exposure
The low levels of radiation you are exposed to during medical tests can be measured in units called millisieverts (mSv).
Some examples of different levels of radiation exposure are listed below.
a single chest X-ray (0.02 mSv) – equivalent to three days of natural background radiation
natural radiation (2.2 mSv) – the average annual dose a person in the UK receives from natural sources
a mammogram (2 to 5 mSv) – the amount of radiation a woman receives after having a mammogram (a type of X-ray used during breast cancer screening); the benefit of detecting breast cancer at an early stage is likely to outweigh the risk of any problems from the radiation exposure
a computerised tomography (CT) scan of the whole body (10 mSv) – the dose is lower for a CT scan of the head or chest; the benefits of having a CT scan usually greatly outweigh any potential risk
working with radiation (20 mSv) – the UK legal limit that a classified person who works with radiation may be exposed to in any given year (as set by the Ionising Radiations Regulations 1999); however, most workers receive considerably less than this
Want to know more?
GOV.UK: patient dose information
Health and Safety Executive: ionising radiation FAQs
World Health Organization: what is ionising radiation?
There's conflicting evidence about the risks faced by people who regularly work with radiation. This includes nuclear power workers and medical professionals who use radioactive technology, such as X-rays and CT scanners.
Some studies have shown people working with radiation have a higher risk of problems such as cancer, heart disease and stroke, while other studies have indicated there's a lower risk of these problems.
Improvements in safety standards mean it's now estimated only 6% of radiation workers are likely to be exposed to high levels of ionising radiation (100mSv or more) during their career, which should reduce the chances of problems developing.
There's also currently no evidence that the children of people who work with radiation have an increased risk of developing serious health conditions, such as birth defects or leukaemia.
Want to know more?
Health and Safety Executive: information on doses