An X-ray is often compared to natural background radiation exposure to help people understand the amount of radiation involved, and in many cases, a single X-ray corresponds roughly to a few days to a few months of natural background radiation, depending on the type of X-ray and the specific background radiation levels.
Natural background radiation is the ionizing radiation that everyone is exposed to continuously from the environment. It comes from cosmic rays from space, radioactive materials in the earth (like uranium, thorium, and radon gas), and even from radioactive elements naturally present in our bodies, such as potassium-40 and carbon-14. This background radiation dose is very low and constant, typically averaging about 3 millisieverts (mSv) per year for most people living at sea level, though it varies by location and altitude.
When you get an X-ray, such as a chest X-ray, the radiation dose you receive is usually around 0.1 mSv. This amount is roughly equivalent to about 10 days of natural background radiation exposure. So, a single chest X-ray is not equal to months but closer to a few weeks of natural background radiation. Other types of X-rays, like dental X-rays, deliver even less radiation—often comparable to just a day or two of natural background exposure. Digital dental X-rays, for example, use 80% to 90% less radiation than traditional film X-rays, making their dose very low.
More complex imaging, such as CT scans, involves significantly higher doses of radiation. A CT scan can deliver doses equivalent to several months or even years of natural background radiation, depending on the scan type and area of the body imaged. For instance, a typical abdominal CT scan might expose a patient to about 10 mSv, which is roughly equivalent to three years of natural background radiation.
It is important to understand that natural background radiation is delivered at a very low and continuous rate, whereas medical X-rays deliver radiation in a short burst at a higher dose rate. This difference in dose rate means that the biological effects of radiation from medical imaging and natural background radiation are not exactly the same, even if the total dose numbers appear similar.
The risk from a single X-ray is generally very small and is considered acceptable given the diagnostic benefits. Medical imaging contributes to about half of the total radiation exposure in some developed countries, but the doses from individual X-rays are carefully controlled to minimize risk. Protective measures, such as lead aprons and thyroid collars, are often used to shield parts of the body not being imaged, further reducing unnecessary exposure.
In summary, while a single X-ray is sometimes said to be “equal to months of natural background radiation,” this is an oversimplification. The equivalence depends on the type of X-ray and the natural background radiation level. A chest X-ray is roughly equal to about 10 days of natural background radiation, dental X-rays are even less, and CT scans can be equivalent to several months or years of background exposure. The continuous low-dose nature of natural radiation and the short, higher-dose bursts from medical imaging mean their biological impacts differ, but both are measured in terms of millisieverts to help gauge exposure and risk.