You can't see, smell, or taste radon gas, and it's everywhere, inside and outside of your home. Radon gas is RADIOACTIVE! When you breath radon and it's decay products in, you expose your lungs to dangerous ionizing radiation. We are exposed to ionizing radiation all the time from several sources, like xrays, CT scans, consumer products, but the ionizing radiation received from radon causes 20 times more damage!
Because radon gas is the leading cause of lung cancer among non-smokers, the leading environmental cause of lung cancer, and the second leading cause of lung cancer after smoking. It is estimated that radon gas causes between 14,000 and 21,000 lung cancer deaths each year in the United States. High levels of radon gas have been found in every home type, in every state, and in every county across the US. High radon levels have even been found in multi-story dwellings. The EPA estimates that about 7% of homes across the US have elevated levels of radon gas above the EPA action level, however, many of the counties in Northern Virginia are much higher than this, with some counties in the 40% range.
Radon is everywhere, inside and outside your home. The question isn't "Do I have radon gas in my home?", the question is "How much radon gas do I have in my home?". While there is no "Safe" level of radon, the EPA has set an action level of 4 pico Curies per liter (pCi/L) If your home has a radon level at or above the action level of 4 pCi/L, you should take steps to reduce it. The EPA also recommends that you "consider" taking steps to reduce the radon level in your home if it's between 2 and 4 pCi/L. A good mitigation professional can usually get the radon level in your home to below 2 pCi/L, regardless of how high it is to begin with. We have found homes in VA with over 100 pCi/L, again, the only way to know what the radon level is in your home is to perform radon testing.
Radon is a radioactive gas that comes from the breakdown of uranium found in soils everywhere on the planet. So radon gas comes primarily from the soil under your home. However, it can also come from building materials which contain uranium or by-products of uranium, and it can also come from the water you use in your home, especially if you get your water from a private well. If there is radon gas in the soil under your home, it will be pulled into your home due to pressure differences. The pressure inside your home is usually less than the pressure outside. The negative pressure inside your home will draw outside air in through gaps and cracks in your floor slab and walls. If there's radon gas in the outside soil and air, it will be drawn in too.