Welcome to the State of California 

Indoor Radon Program

The Indoor Radon Program, within the Environmental Management Branch, seeks to reduce the health risk from radon exposures by increasing awareness, providing information about testing, identifying areas of high radon potential, and promoting mitigation and radon-resistant construction.   

New! Special Report 226 - Radon Potential in San Mateo County

The California Department of Public Health, in partnership with the California Geological Survey, is developing detailed radon potential maps for regions of the state. The latest map and report, covering the County of San Mateo, has been released. See all reports here.

What is radon?

Radon is a naturally occurring radioactive gas that is odorless, invisible, and without taste.  It is released during the natural decay of uranium, which is present in most rock, soil and water. Its occurrence in the state is influenced primarily by geology; find out more about radon.

Where is radon found?

Radon can be found throughout California because uranium exists in all rock and soil.  Although certain areas of the state are more likely to contain higher radon levels than others, radon is a house-to-house issue.  You may live in an area of low radon potential yet your house can have elevated radon but your neighbor's house has a low radon level. 

Radon, in its natural state cannot be detected with the human senses. The only way to detect radon is to test.  California residents can purchase low cost radon test kits,
Home Test Kits $7.95
, to test their home.  The results of the test should determine if you and your family are at risk. 

Testing for real estate transactions must be conducted by a California certified radon tester.  If the tester is not on the service providers list, he or she may not be certified or registered with the Indoor Radon Program.  Certification and registration for service providers is a requirement in California; (Radon and Real Estate). 

How does radon enter into my house and what can I do?

As the radon gas escapes from the ground into the air, the lower air pressure inside your home draws the outside air in through cracks, seams and other openings in your home foundation; (How Radon Enters Into My House).  If you have elevated radon levels you can still fix your home.  The California Department of Public Health (CDPH) along with U.S. Environmental Protection Agency (US EPA) recommends that you fix your house if it has 4 picocuries per liter (4 pCi/L) or higher.  If you are building a house in an area of moderate or high radon potential, we recommend using radon-resistant building techniques. 

Why do I need to be concerned about radon?

Radon is the second leading cause of lung cancer (PDF)Opens in new window., following smoking.  US EPA estimates (PDF)Opens in new window.that nationally 21,000 lung cancer deaths are caused by radon each year.   

Additional Information 

Frequently Asked Questions (PDF) Opens in new window.

Why Build Radon Resistant?          

Granite Counter Tops and Radon Concerns (PDF)Opens in new window.

Health Physics Society response to use of Geiger-Mueller detectors for granite counter tops (PDF) Opens in new window. 


 Contact Information

California Department of Public Health
ATTN:  Radon Program Manager, Radonprogram@cdph.ca.gov; (916) 449-5674; Fax (916) 449-5665
Indoor Radon Program, 1616 Capitol Avenue, MS 7404
P.O. Box 997377
Sacramento, CA  95899-7377  


For More Information

World Health Organization
Last modified on: 12/29/2014 11:20 AM