Hot nights not only prevent rest, but also directly influence health and mortality rates worldwide. This is the main conclusion of an international study led by the Spanish National Research Council (CSIC) that analyzed the effects of nighttime air temperature in 178 locations in 44 countries between 1990 and 2018. The research, carried out through research institutes in Catalonia, Galicia, and Andalusia, found a mortality rate of up to 3%.