Any dose of ionizing radiation can increase our lifetime cancer risk, but low doses of radiation increase the risk of cancer by only a small amount. The evidence for this comes from a number of studies that have looked carefully at cancer rates in large groups of people with various levels of radiation exposures; this includes people who survived the atomic bombs that were dropped on Japan, people who have been exposed to radiation at work, and people who have lived for a long time in homes with high radon levels.