Signs of heat illness include nausea, weakness, fainting and pale, clammy skin. Often, the skin turns red and dry, providing a warning signal of heat illness. According to NOAA, there are four kinds of heat-related illnesses. Sunburn is redness and pain in the skin, with possible swelling, blisters, fever and headache. Heat cramps are described as heavy sweating and painful spasms, usually in the legs or abdominal muscles.
Heat exhaustion is the stage before heat stroke where sufferers become weak and sweat heavily.
The skin is cold, pale and clammy, the pulse becomes weak and rapid, and the person faints or vomits. Heat stroke can cause a person to lose consciousness, and is defined as a body temperature of 106 or higher along with hot, dry skin and a rapid, strong pulse. The first defense against heat illness is prevention. Avoid heavy physical exertion in the middle of the day. Keep windows open for ventilation in cars or houses without air conditioning.