Welcome to the State of California 


Radon is a naturally occurring gas found in soil, rocks, and water throughout California and the world. Radon has no color, odor, or taste. The gas can move from the ground into homes, schools, and other buildings and is our largest exposure to naturally occurring radiation.1

Radon leaks inside buildings through cracks and holes in the slab or foundation. The air pressure in the ground is usually higher than in buildings, so the outside pressure pushes radon gas through small openings in a building’s structure.

Radon Gets In Through:

  1. Cracks in solid floors
  2. Construction joints
  3. Cracks in walls
  4. Gaps in suspended floors
  5. Gaps around service pipes
  6. Cavities inside walls
  7. The water supply

From “A Citizen's Guide to Radon: The Guide to Protecting Yourself and Your Family from Radon.” Click here to read the entire U.S. Environmental Protection Agency (EPA) brochure.

Click here to go to the CDPH Indoor Radon Program web site.

Click here to learn about the geology of radon.

What are the health effects of radon?

Radioactive particles from radon can damage cells that line the lungs and lead to lung cancer.2 This is the most common type of cancer, with smoking as the leading cause and radon as the second leading cause of lung cancer.3 The EPA estimates that each year over 20,000 lung cancer deaths are radon related,4 greater than the number estimated to be due to exposure to second-hand tobacco smoke.5

The risk of lung cancer is higher for non-smokers exposed to radon than those not exposed, and radon-exposed smokers are at an even greater risk because radon and cigarette smoke work together to cause lung cancer.6

Click here to find out more about the health risks from radon.

From “A Citizen's Guide to Radon: The Guide to Protecting Yourself and Your Family from Radon.” Click here to read the entire EPA brochure.

What is CDPH's position on testing for radon?

CDPH agrees with the recommendations of the EPA and the U.S. Surgeon General that all schools be tested for radon and that homes be tested below the third floor. Radon concentrations are much lower above the second story.7

Are there related policies?

If you are building a house in an area of moderate or high radon potential, the EPA recommends using radon-resistant building techniques.

Click here to learn more about radon-resistant home design and construction.


1 Radon (chemical symbol Rn) is a naturally occurring radioactive gas found in soil, rock, and water throughout the U.S. and the world. It has numerous different isotopes, but radon-220 and -222 (220Rn and 222Rn) are the most common (http://www.epa.gov/rpdweb00/radionuclides/radon.html).

2 Long-term exposure to radon can lead to lung cancer, the only cancer proven to be associated with inhaling radon (http://www.cancer.gov/cancertopics/factsheet/Risk/radon).

3 Lung cancer is the leading cause of cancer deaths in the United States, among both men and women (http://www.mayoclinic.com/health/lung-cancer/DS00038). It claims more lives each year than colon, prostate, lymph, and breast cancers combined.

4 Smoking is the leading cause of lung cancer. Smoking causes an estimated 160,000 cancer deaths in the U.S. every year (American Cancer Society, 2004) (http://www.epa.gov/radon/healthrisks.html).

5 Secondhand smoke is the third leading cause of lung cancer and responsible for an estimated 3,000 lung cancer deaths every year (http://www.cancer.gov/cancertopics/factsheet/Tobacco/ETS)

National Cancer Institute. Cancer Progress Report 2003 .

Public Health Service, National Institutes of Health, U.S. Department of Health and Human Services, 2004.

6 The National Research Council report: "Health Effects of Exposure to Radon: BEIR VI, Committee on Health Risks of Exposure to Radon (BEIR VI)" by the National Academy of Sciences (NAS) is the most definitive accumulation of scientific data on indoor radon (http://www.nap.edu/openbook.php?record_id=5499). The report confirms that radon is the second leading cause of lung cancer in the U.S. and that it is a serious public health problem (http://www.epa.gov/radon/beirvi.html).

7 Because most indoor radon comes from naturally occurring gas in the soil, high indoor levels are more likely to exist below the third floor (http://www.epa.gov/radon/pubs/tenants.html). In some cases, high radon levels have been found on upper floors due to radon movement through elevators or other air shafts in a building.

Last modified on: 5/14/2014 12:10 PM