What Is Background Radiation? Sources and Risks

Sources of Background Radiation
Sources of background radiation include radon gas, buildings, rocks, food, nuclear tests, and cosmic rays.

Background radiation is ionizing radiation present in the natural environment. It does not include non-ionizing radiation, like visible light or radio waves, nor does it include intentional radiation, like in radioactive sources or research or man-made items, like Fiestaware glaze. Ionizing radiation includes alpha, beta, gamma, x-rays, and neutrons.

Background radiation occurs everywhere. The amount varies from one place to another, but usually poses no health risk.

Sources of Background Radiation

Various references assign slightly different values to the amount of background radiation attributable to various sources. This is because its composition isn’t the same everywhere. But, approximately half of background radiation (or more, depending where you live) comes from radon isotopes, roughly 12% comes from artificial sources; about 11% comes from cosmic rays; about 11% comes from rocks, minerals, and building materials; and around 5% comes from food and drink.

Background Radiation Pie Chart
Most background radiation exposure comes from radon gas, but space, the ground, building materials, and potassium-40 in food also contribute.

Specific background radiation sources include:

  • Radon gas from the ground
  • Cosmic rays (altitude affects the exposure, so highest in aircraft and on the ISS)
  • Plants that absorb isotopes from soil and water
  • Food, especially produce high in the isotope potassium-40
  • Natural radioisotopes in water
  • Natural radioisotopes in rocks and minerals, especially uranium and thorium
  • Isotopes in building materials, such as limestone, concrete, and bricks
  • Medical tests, mostly from CT scans, plus some from x-rays and other nuclear medicine (radiation for cancer treatment is not considered background)
  • Nuclear weapons testing
  • Nuclear and coal power
  • Nuclear accidents
  • Depleted uranium shells
  • Cigarettes (from polonium)

How High Is Background Radiation?

Background radiation comes from both natural and artificial sources. It is present everywhere, but the amount varies widely from place to place and also depends on where a person works. The average annual effective dose ranges between 2 and 4 mSv. Places where dose rates exceed 10 mSv/year are considered high natural background radiation (HNBR) regions. For example, background radiation in Ramsar, Iran is 6 to 131 Sv/year (mostly from naturally radioactive limestone and radon).

Background Radiation Risks

While it’s a good idea to avoid unnecessary radiation exposure, background radiation usually doesn’t present a health risk. Human cells have many repair mechanisms to repair damage from ionizing radiation. Also, the benefit from some radiation sources greatly outweighs their risk. For example, potassium from bananas naturally includes a tiny amount of potassium-40, but the element is essential for human nutrition. A mammogram results in 42 mrem (0.42 mSv) of x-ray exposure, yet early cancer detection is more beneficial than the tiny risk from the radiation.

Researchers examining a possible link between background radiation and cancer have not found an unequivocal link between the two, despite theoretical models that predict any increase in radiation dose should result in a proportional increase in disease. There are many confounding variables that make it difficult to establish a link between background radiation and negative health effects. Some studies even point to a slight health benefit from radiation.

Also, the type of risk depends on the radiation source. For example, inhaling radon or smoking cigarettes is more likely to cause lung cancer. Exposure to strontium-90 from nuclear testing or waste is more likely to cause bone cancer. The dose, duration of exposure, and which body part is exposed also factor into risk.

So, reducing risk from background radiation involves lessening exposure to controllable radiation sources. For example, reducing risk from radon exposure includes sealing cracks in floors and walls and increasing building ventilation. Reducing risk from cosmic rays involves limiting time at high altitude.


  • Dobrzyński, L.; Fornalski, K.W.; Feinendegen, L.E. (2015). “Cancer Mortality Among People Living in Areas With Various Levels of Natural Background Radiation”. Dose-Response. 13 (3): 1–10. doi:10.1177/1559325815592391
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