Like an engine, the human body has ways of keeping itself cool, such as letting heat escape through the skin, and perspiring.
But in heat waves, if people's bodies do not cool properly, they can end up with a heat-related illness.
"Basically what happens in a true heat stroke, the most serious of all the heat illnesses, is that the body's temperature regulating system shuts down," Dr. Tim Johnson told ABCNEWS' Good Morning America. "The lack of perspiration that occurs is one part of it."
Johnson said the internal body temperatures can skyrocket past 105 degrees. "It's like frying your own tissues," he said. "It destroys cells. The brain is destroyed, the heart and the kidneys."
Heat strokes can really happen to anyone, but such illnesses most often strike the very young, or the elderly. Heat-related illnesses can be serious, and even deadly. However, they come on gradually in stages.
The first stage is painful heat cramps in the muscles. Anyone who experiences them should stop the activity they are doing and rest. If someone suffering from the cramps is awake and alert, have them drink water or a sports drink, and stretch the muscle for 20 seconds, then massage it.
According to the American Red Cross, the following are signals of heat exhaustion, the more serious stage of heat-related illness: cool, moist, pale skin (or skin could be red right after physical activity), headache, dizziness and weakness or exhaustion; nausea; skin may or may not feel hot.
The signs of a late stage heat-related illness (often called heat stroke) include: vomiting, decreased alertness level or complete loss of consciousness; high body temperature (sometimes as high as 105 degrees Fahrenheit); skin may still be moist or the victim may stop sweating and the skin may be red, hot and dry; rapid, weak pulse; rapid, shallow breathing. If someone is experiencing any of these symptoms, call 911.
For heat cramps or heat exhaustion, get the person suffering from it to a cooler place, where they can rest. Give them a half glass of cool water every 15 minutes, and have them drink slowly. No alcohol or caffeine drinks. Remove or loosen tight clothing and apply wet cloths.
If someone has signs of heat stroke, get help fast by calling 911. Move the person to a cooler place, make them lie down and wrap wet sheets around their body. Watch for breathing problems and make sure the person's airway is clear. They should remain lying down.
To prevent heat-related illness, follow these tips:
Dress for the heat in lightweight, light-colored clothing.
Drink water even if you're not thirsty, but avoid alcohol and caffeine.
Eat small meals, and eat more often.
Avoid using salt tablets, unless directed by a physician.
Slow down — avoid strenuous activity, but if you must exercise, do so in the morning between 4 a.m. and 7 a.m.
Stay indoors when possible.
Take regular breaks when engaged in physical activity.