People suffer heat illness when the body’s temperature control system is overloaded. The body normally cools itself by sweating. If the body loses too much water through sweating, it can have a negative effect on the cardiovascular system. Sometimes sweating just isn’t enough and a person’s body temperature rises rapidly. Very high body temperatures may damage the brain or other vital organs. This can be fatal.
(This answer provided for NATA by the Marist College Athletic Training Education Program.)