Radiation is a form of energy in waves which exists on a spectrum with low frequency radiation from radio waves as well as microwaves on the low end and which also exists on a spectrum with high frequency radiation from gamma rays as well as x rays on the high end. The lower the frequency radiation of the waves and the lower the exposure, the less dangerous it is but all the radiation affects the cells in our bodies to some extent. Some sources of the environmental radiation include radon gas in the home, mineral potassium in the body, radiation from outer space, radioactive compounds in soil and building materials, etc.
It is well established that the exposure to the large amounts of radiation at once can also cause acute sickness as well as even cancer. There are some enzyme systems in the body which repair damages from these low levels of background radiation but even small levels of these radiation exposure may impact cancer risks later in life. Some other various sources of the radiation exposure includes abdominal CT scan, living in Denver, mammogram, living at sea level, chest x ray, smoking, living within 50 miles of a nuclear power plant, dental x ray, banana, etc.