In humans, high temperatures combined with high humidity can cause feelings ranging from discomfort to life-threatening conditions. A heat wave in Switzerland is defined as a period of very warm weather lasting several days. The threshold value is defined by the American heat index, which comprises temperature and humidity. Elderly and sick people are particularly susceptible to changes in temperature. Individuals who are physically very active and those in extremely hot environments (cars without air-conditioning, offices behind glass windows, etc.) are also at high risk. As the climate changes, it is quite likely that heat waves will occur much more frequently in the future.