TEETH AND LIMBS
Less than a day and a half
A single dental bitewing or an X-ray of an arm or ankle is under 0.01 mSv, less than 1.5 days of natural background radiation.
Compare scansStart
WHAT THE FIGURES SAY
A few days of
background, in a blink.
Radiation is all around us, all the time.
Rocks, soil, the air and even food give everyone a small dose every year. UK health guidance compares each X-ray with that natural background, which makes the numbers far easier to picture.
MILLISIEVERTSmade easier to picture
Compare an X-rayKeep in mind
- Teeth and limbs: tiny
- Chest: about 3 days
- CT: years, not days
- Every scan weighed up first
THE SHORT ANSWER
Most X-rays are
a very small dose.
UK guidance puts each scan side by side
with the radiation we all get naturally.
BIGGER SCANS
CT is a different scale
A CT scan of the chest is about 8 mSv, roughly 3.6 years of background. Doctors weigh the benefit before offering one.
See the numbers
HISTORY
Found by accident in 1895
Wilhelm Röntgen noticed a faint glow on a nearby screen while studying cathode rays. He won the Nobel Prize in Physics in 1901.
Where they came fromGeneral information only, not medical advice. For advice about your own health, speak to a doctor, pharmacist or other qualified health professional.
A QUICK COMPARISON
How big is
that X-ray?
Pick a common examination to see its typical dose and how long it would take to get the same amount from natural background radiation in the UK. The bar shows the relative size of the dose.
Typical figures from UK Health Security Agency guidance. Your own dose may differ. This is general information, not medical advice.
TWO NUMBERS WORTH KNOWING
Background first,
then the scan.
One figure for a common X-ray,
one for what everyone gets each year.
≈ 3 days
Natural background it equals
UKHSA patient guidance puts a single chest X-ray at about 0.02 mSv, about the same as 3 days of natural background radiation.
CHEST X-RAY · UKHSA
2.6 mSv
UK average annual radiation dose
UKHSA's dose comparisons give 2.6 mSv as the average annual dose in the UK, of which radon contributes 1.3 mSv on average. A transatlantic flight is about 0.08 mSv.
EVERY YEAR · UKHSA
UKHSA's two pages use slightly different typical figures for a chest X-ray (0.02 and 0.014 mSv), because doses vary with equipment and patient. Both are a tiny fraction of a year's background.
FOUR THINGS TO KNOW
Quick, painless
and weighed up.
What the NHS says to expect, so the appointment holds no surprises.
Step 1
Say if you might be pregnant
Tell the healthcare professional if you are or might be pregnant, or if you are breastfeeding.
Step 2
Expect a few minutes
The images take only a few minutes. You hold still while the radiographer steps behind a screen.
Step 3
Allow time after contrast
If you have barium or contrast dye, you may be asked to wait up to 30 minutes to check for a reaction.
Step 4
Ask when results come
You should be told when to expect them. If you hear nothing after a few weeks, contact the doctor who referred you or your GP.
WHERE THEY CAME FROM
A glow in
a dark lab.
In 1895 the German physicist Wilhelm Röntgen was studying cathode rays at Würzburg when he noticed a faint glow on light-sensitive screens nearby. He had found a new, penetrating kind of radiation.
The rays were later named after him in many languages, and in 1901 he received the Nobel Prize in Physics for their discovery. Today X-rays are used to check bones for breaks, spot tooth decay and look at the lungs and digestive system.
Questions
Questions on the way
How much radiation is in a chest X-ray?
UKHSA patient guidance gives about 0.02 mSv, similar to 3 days of natural background radiation. Its separate dose comparison table lists 0.014 mSv.
Are dental X-rays safe?
The NHS says X-rays are usually very safe. A single dental bitewing is under 0.01 mSv, less than a day and a half of natural background, according to UKHSA.
Is a CT scan the same as an X-ray?
CT uses X-rays but takes many images, so the dose is higher. UKHSA gives about 8 mSv for a CT of the chest, roughly 3.6 years of natural background.
Where does natural background radiation come from?
From the ground, buildings, the air, food and space. UKHSA says radon gas alone gives people in the UK an average of 1.3 mSv a year, and much more in places such as Cornwall.
Should I worry about having several X-rays?
The NHS says many X-rays carry a very small risk of causing cancer, and your doctor weighs this before offering one. Ask them if you have concerns.
Destination