Natural background radiation is all around us. Background radiation varies from place to place and over time, depending on the amount of naturally-occurring radioactive elements in soil, water and air. Weather conditions also affect radiation levels, as snow cover may shield these elements, and radioactive particulates can wash out of the air during rain storms. Cosmic radiation from the sun, our galaxy, and beyond is constantly around us and contributes to natural background radiation. Altitude and latitude can also influence the level of background radiation at any one site.
All rocks and soils contain some trace amount of natural radioactivity and can sometimes be ingested or inhaled if disturbed. Radon is a gas that can concentrate indoors and be inhaled, along with its decay products. We can also ingest radioactivity from the food we eat and the water we drink.
A number of factors determine the annual dose you and your family receive from background radiation. The following chart shows the percentage of background radiation dose received annually from various natural sources.
Source: National Council of Radiation Protection and Measurements (NCRP), Report 160
To estimate your personal yearly radiation dose from the most significant sources of ionizing radiation, please visit Calculate your Radiation Dose.
For more information on background radiation, visit Radiation Sources and Doses.
For more information on radon and how it may affect you and your family, visit the EPA's Radon web area.