"How Hot Is Too Hot For The Human Body?"

Given that it is summer and Europe is having summer temperatures similar to what you see in the United States, The Conversation has published what seems a timely article on "How hot is too hot for the human body? Our lab found heat + humidity gets dangerous faster than many people realize." The authors first lay out what is the current consensus:

    People often point to a study published in 2010 that estimated that a wet-bulb temperature of 35 C – equal to 95 F at 100% humidity, or 115 F at 50% humidity – would be the upper limit of safety, beyond which the human body can no longer cool itself by evaporating sweat from the surface of the body to maintain a stable body core temperature.

    It was not until recently that this limit was tested on humans in laboratory settings. The results of these tests show an even greater cause for concern.

The article then briefly describes how the authors conducted their research before getting to their findings:

    That combination of temperature and humidity whereby the person’s core temperature starts to rise is called the “critical environmental limit.” Below those limits, the body is able to maintain a relatively stable core temperature over time. Above those limits, core temperature rises continuously and risk of heat-related illnesses with prolonged exposures is increased.

    When the body overheats, the heart has to work harder to pump blood flow to the skin to dissipate the heat, and when you’re also sweating, that decreases body fluids. In the direst case, prolonged exposure can result in heat stroke, a life-threatening problem that requires immediate and rapid cooling and medical treatment.

    Our studies on young healthy men and women show that this upper environmental limit is even lower than the theorized 35 C. It’s more like a wet-bulb temperature of 31 C (88 F). That would equal 31 C at 100% humidity or 38 C (100 F) at 60% humidity.

The authors also warn:

    Keep in mind that these cutoffs are based solely on keeping your body temperature from rising excessively. Even lower temperatures and humidity can place stress on the heart and other body systems. And while eclipsing these limits does not necessarily present a worst-case scenario, prolonged exposure may become dire for vulnerable populations such as the elderly and those with chronic diseases.