How hot is too hot for the human body?

Research shows that the combination of temperature and humidity can get more dangerous faster than scientists previously believed. 

Scientists and other observers have become alarmed about the increasing frequency of extreme heat paired with high humidity, measured as “wet-bulb temperature.” A 2010 study estimated the wet bulb temperature of 95 F at 100% humidity or 115 F at 50% humidity as the upper limit of safety. Recently this limit was tested on humans in a laboratory setting and showed that the wet-bulb temperature is actually 88 F at 100% humidity or 100 F at 60% humidity.

The combination of temperature and humidity whereby a person’s core temperature starts to rise is called the “critical environmental limit.” 

• Below those limits, the body is able to maintain a fairly stable core temperature over time.
• Above those limits, core temperature rises continuously, and the 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 disperse the heat. When you're also sweating, it decreases body fluids.
• In the worst case, prolonged exposure can cause heat stroke.