France, July 31 -- "Extreme heat causes the bronchi to constrict. This bronchoconstriction leads to breathing difficulties," Professor Colas Tcherakian, a pulmonologist and consultant at Foch Hospital near Paris, told RFI. "You may feel unwell, even without having a respiratory condition."

"With the succession of heatwaves, we are learning that anyone can end up in hospital with a respiratory infection," Tcherakian added.

"It has now been clearly demonstrated that, when a heatwave lasts more than three days, the risk of developing this type of infection increases by 70 percent: that's enormous."

Heat affects the range and circulation of bacteria, viruses, mould and other pathogens, while also reducing the body's ability to fight infect...