The vast majority of people are exposed to some level of radioactivity every day, whether through medical imaging, air travel, or even eating certain foods like shrimp. According to a report by the Nuclear Safety and Radiation Protection Authority (ASNR), published on September 28, the average annual dose of radiation for the general population is 7.1 millisieverts (mSv), with significant variation depending on individual circumstances. For comparison, the regulatory limit for the general public exposed to nuclear activities is 1 mSv per year, while workers in such environments can be exposed to up to 20 mSv annually. "This dose mainly comes from exposure to radon, which accounts for about 55 percent of the total," says Éric Blanchardon, who oversees the evaluation of radiological and nuclear risks at the ASNR. "We estimate an average dose per person of 3.9 mSv per year, with variations ranging from 1.4 to 9.4 mSv per year." Radon is a radioactive gas that forms naturally from the decay of radionuclides in the soil. It is particularly common in regions like Brittany, the Massif Central, Corsica, and the Vosges, where the soil contains high levels of uranium and granite. Radon tends to accumulate in older buildings constructed with local stone, especially those with basements, earthen floors, and poor ventilation. This can lead to dangerous concentrations of the gas. Radon is the second leading cause of lung cancer after smoking, which is why it is recommended to properly ventilate homes, especially in winter, in areas where radon levels are high. However, this may not always be enough. "If measurements show radon levels above a reference level of 300 becquerels per cubic meter (Bq/m³), we investigate the cause," explains Carole Rousse, director of ionizing radiation and health at the ASNR. "If levels exceed 1000 Bq/m³, it is necessary to reduce exposure and carry out remediation work if possible." Radon is not the only source of radiation in our living spaces. People living in high mountain areas are also exposed to cosmic radiation, which comes from particles originating in space. The dose from this source is 0.3 mSv per year at sea level, but increases to 0.8 mSv per year at altitudes above 2000 meters. For example, in Tignes (Savoie), the dose was 0.82 mSv in 2024. Long flights can also increase exposure to cosmic radiation. Other areas may have higher levels of terrestrial radiation due to naturally occurring radionuclides in the Earth's crust. Medical imaging, however, is the second largest contributor to radiation exposure, with an average dose of 1.6 mSv per year per person. This varies widely, as some people receive no medical radiation, while others may receive significant doses. "The most common examinations are conventional radiology, including dental X-rays. However, the most significant contributors to radiation exposure are CT scans and, to a lesser extent, nuclear medicine," says Éric Blanchardon. "For all medical exposure, it is always a risk-benefit balance." Should people avoid preventive exams like mammography, which is recommended every two years for women aged 50 to 74? "For all medical exposure, it is always a risk-benefit balance. If mammography is offered to a woman, it is because there is a benefit, and it is well considered in breast cancer screening programs," reassures Carole Rousse. Other factors, such as diet and tobacco use, contribute about 9 percent of the average radiation dose, or 0.65 mSv per year. The consumption of certain seafood, such as mussels, oysters, shrimp, and crabs, which contain polonium 210, can add up to 1.3 mSv per year for those who eat large amounts of seafood (around 50 kg per year). The nuclear industry contributes very little to overall radiation exposure. According to the ASNR, the dose from nuclear installations is extremely low: between 0.0001 and 0.01 mSv per year for people living within 10 km of a nuclear reactor or radioactive waste facility, and 0.002 mSv per year within a 1 km radius of a cyclotron. Fallout from nuclear tests and the Chernobyl accident also contributes an estimated 0.005 mSv per year, with 90 percent coming from atmospheric nuclear tests and 10 percent from Chernobyl. However, some areas in eastern France, still contaminated with cesium 137, require continued vigilance. "A person working outdoors in non-remediated areas may receive a higher dose," says Éric Blanchardon. "Consuming game meat or mushrooms, which tend to accumulate radionuclides, can also increase exposure." While radiation exposure is unavoidable, it is not entirely risk-free. A study published in January 2012 by the National Institute of Health and Medical Research (Inserm), in collaboration with the IRSN (now the ASNR), found a higher incidence of leukemia in children under 15 living within 5 km of a nuclear power plant. "Today, the available scientific data do not allow us to determine a threshold dose below which we could be sure there is no risk," says Énora Cléro, an epidemiologist at the ASNR. "This means that the lower the dose, the lower the risk, and the higher the dose, the higher the risk. For the lowest doses, there is a possible long-term risk of cancer, and the probability of developing cancer decreases with the dose." To assess radiation exposure accurately, the ASNR conducts extensive environmental monitoring, collecting over 8,000 samples per year from air, water, soil, marine environments, and food, as well as more than 50,000 radon measurements. For those interested in understanding their own radiation exposure, the ASNR has created an online questionnaire to help individuals determine their level of exposure.