Humans have always been exposed to natural radiation—whether from external sources (such as space and rock formations) or through internal exposure resulting from the intake of naturally occurring radioactive elements (radionuclides) via inhalation and diet. As is so often the case, the dose matters. Today, we are able to measure this radiation and compare, for instance, the exposure caused by building materials used in a home against the limit value recommended by the International Commission on Radiological Protection (ICRP). This makes it possible to determine whether the measured levels exceed the average exposure for a given region. More on the subject of radiation