How much heat can the human body withstand?

How much heat can the human body withstand?

Heat deaths have become quite common, and as the world heats up, they may become even more common unless a plan is developed for extreme heat days, like the kind of warning system that usually comes before a major storm.

Heat can kill because our bodies are made up of membrane-encased cells that, if heated enough, will melt. While we think of ourselves as warm-blooded animals, biologists would call us homeothermic—we must maintain a core temperature within a narrow range of about 98 F (36.6 degrees Celsius).

Our core can survive up to 104 F (40 degrees Celsius) for a short time without permanent damage, said Sam Cheuvront, a heat physiologist who worked for the US Army Research Institute.

Our bodies cool down by sending blood to the skin, where it dissipates heat into the air. But that only works until the air temperature is around 95 F (35 degrees Celsius), he said.

Then there is only one way to cool down, and that is to sweat. Sweat isn't what keeps you cool - it's the process of sweat evaporation.

Human bodies heat up much faster in direct sunlight than at the same temperature in the shade. Airflow can help sweat evaporate and allow body heat to dissipate.

Most heat-related deaths are not due to heatstroke, Jay said. The elderly and people with heart disease are more at risk of heart attack because the body's cooling mechanisms create cardiovascular stress when pushed too hard. Others die of kidney failure from a combination of blood being pulled from the kidneys and dehydration.

Once the body's core temperature starts to rise above 104 F (40 degrees Celsius), things get dangerous very quickly. If it reaches 106 F (41 degrees Celsius), you are likely to suffer fatal heat stroke.

People can adapt to the heat for a few days in a hot place. They will begin to sweat faster, lower their core temperature and increase fluid volume. But eventually the heat can overcome all these natural adaptations.