Radon is found at very low levels in outdoor air.

It is found at higher levels in indoor air in homes, schools, and office buildings.

Cracks in the basement or foundation of a home may allow higher levels of radon inside the home. However, sealing alone is not an effective way of reducing radon.

Indoor radon levels are affected by the radium and uranium levels in soil, the porosity of the soil, the composition and condition of the foundation materials, and the ventilation rate of the room.

Miners, particularly those who mine uranium and hard rock, are exposed to higher levels of radon.