Serge Bouthez at the Pont de Lunel campsite in France, during a heatwave, August 12, 2025. CLAIRE GABY/ DIVERGENCE FOR LE MONDE
At every age, heat can pose a health risk. Since August 8, the start of the summer's second heat wave, the number of emergency room visits related to heat has increased to more than 100 per day, Santé Publique France (SPF, France's national public health agency) reported in its Heat Wave and Health bulletin published on Wednesday, August 13. The rise was particularly sharp among 15 to 44 year olds (up 100%), mainly due to hyperthermia and heat stroke. Between August 8 and August 11, 45% of the population experienced at least one day of orange-level weather alert, SPF noted.
During the first heat wave of the summer, which affected 60 administrative departments between June 19 and July 6, there were 480 more deaths than usual recorded in France, according to SPF's initial estimates. These figures will be refined in a full report in September. People over 75 paid a particularly heavy toll, making up 85% of this excess mortality from all causes.
Unlike other animal species whose internal temperature fluctuates with their environment, humans must keep their bodies within a range of 36°C to 38°C for cells to function properly. The thermoregulation system is managed by the hypothalamus, a small almond-sized gland at the base of the brain, as well as by a network of receptors in the skin and muscles.
