Is there more radioactive radiation at high altitudes than, say, at sea level?

Answer

Indeed, at high altitudes there is more ionizing radiation, which is potentially carcinogenic. There is a lot of radiation in space, coming from the sun and all kinds of other radiation sources in the cosmos. It is largely blocked by the atmosphere around the earth. Given that half the sky is below 5,000 meters, you can understand that there is even more radiation intensity at the altitudes of long-haul flights, which go up to 10,000 meters or more. Just like personnel who work in a radiation sector, such as in hospitals or nuclear power plants, aviation personnel are also checked with similar procedures. But for those who only occasionally make an airplane trip, this is not a big problem.