Welcome to the State of California 

What Is Radon?

Radon is a cancer-causing, radioactive gas. You can’t see radon.  And you can’t smell it or taste it.  But it may be a problem in your home. Radon comes from the natural (radioactive) breakdown of uranium in soil, rock and water and gets into the air you breathe. It can get into any type of building—homes, offices, and schools—and result in a high indoor radon level.  You and your family are most likely to get your greatest exposure at home, where you spend most of your time. Radon has been found in every county in California. Every Californian is encouraged to test their home.

The Surgeon General has warned that radon is the second leading cause of lung cancer in the United States today.  Only smoking causes more lung cancer deaths.

According to EPA estimates, exposure to radon is responsible for about 21,000 lung cancer deaths every year, more than drunk driving, household falls, drowning, or home fires. That’s because when you breathe air containing radon, you can get lung cancer. Not everyone exposed to radon will get lung cancer, but the greater the amount of radon and the longer the exposure, the greater the risk of developing lung cancer. Lung cancer is the only health effect which has been definitively linked with radon exposure. There is no evidence that other respiratory diseases, such as asthma, are caused by radon exposure and there are no immediate symptoms from exposure to radon. Smokers are at higher risk of developing radon-induced lung cancer.

Radon is a risk at any level. The EPA recommends fixing your home if the radon level is 4pCi/L (pico Curies per liter) or more. However, some health risk remains at any level of radon:


Radon Level

If 1,000 people who never smoked were exposed to this level over a lifetime*...


The risk of cancer from radon exposure compares to**...


What to do:

20 pCi/L

About 36 people could get lung cancer

35 times the risk of drowning

Fix your home

10 pCi/L

About 18 people could get lung cancer

20 times the risk of dying in a home fire

Fix your home

8 pCi/L

About 15 people could get lung cancer

4 times the risk of dying in a fall

Fix your home

4 pCi/L

About 7 people could get lung cancer

The risk of dying in a car crash

Fix your home

 2 pCi/L

 About 4 person could get lung cancer

 The risk of dying from poison

Consider fixing between 2 and 4 pCi/L

1.3 pCi/L

About 2 people could get lung cancer

(Average indoor radon level)

(Reducing radon levels below 2 pCi/L is difficult.)

0.4 pCi/L


(Average outdoor radon level)

(Reducing radon levels below 2 pCi/L is difficult.)

Note: If you are a former smoker, your risk may be higher.
* Lifetime risk of lung cancer deaths from EPA Assessment of Risks from Radon in Homes (EPA 402-R-03-003).
** Comparison data calculated using the Centers for Disease Control and Prevention's 1999-2001 National Center for Injury Prevention and Control Reports.




Last modified on: 10/21/2015 6:00 PM