What is the major cause of heat stroke? Ignorance — of our own bodies, of the weather and of what one can do to the other.

Most people, for example, would say that they are much more comfortable when air temperatures are in the 90s than when they are in the 40s or 50s. Few realize, however, that the body can handle cold air a lot better than hot. Our normal body temperature is around 98.6° Fahrenheit. An increase of only 5 or 6 degrees, however, can be life-threatening. At 104 degrees, we will become very sick; at 106 the brain starts to die; few people reach 113° and survive.

Keeping cool on hot, humid summer days is not just about comfort, according to the Pennsylvania Medical Society, which has issued a special warning that heat stroke is a deadly illness to be avoided at all costs — even if it means skipping your morning run or a day at the beach.

"Heat stroke is not an accident," says Marilyn J. Heine, M.D., an ER physician and member of the Pennsylvania Medical Society. "Over the summer, we see too many cases of heat-related illness in the emergency room, but it's a condition that generally can be prevented with a little effort and lots of common sense."

There have been several news stories about athletes and heat stroke in recent years, most notably Minnesota Viking Korey Stringer, who died in 2001 from multi-organ system failure.

Non-athletes are equally at risk. Dr. Heine recalls a 78-year-old woman who came into the ER with a temperature of 104.7 degrees and a decreased blood pressure of 100/70. Fortunately, she was resuscitated with IV fluids and then hospitalized.

There are two types of heat stroke. Classic or non-exercise-induced heat stroke affects those exposed to hot environments for an intolerable length of time. Dr. Heine explains, "Most at risk are elderly persons and infants, those with chronic illness like cardiovascular disease, and people on certain medications. Individuals who drink large amounts of caffeine and alcohol during this time also are more susceptible."

Exertional or activity-induced heat stroke, on the other hand, "primarily affects persons who overdo physical activity in very hot temperatures," according to Dr. Heine. Football players — who wear body-covering uniforms and practice in the hottest temperatures — are especially prone to dehydration and heat stroke.

When should you watch out for heat stroke? Humidity over 70 percent and air temperatures of 95 degrees Fahrenheit or higher are good warning signs. Also, be alert for symptoms such as cramps, headache, dizziness, nausea, elevated temperature or profuse sweating. Any of these can indicate imminent heat stroke.

"If you exhibit any of these symptoms," Dr. Heine advises, "get out of the heat, rest, and drink plenty of cool fluids, preferably containing sugar and salt."

Heat stroke's symptoms include profuse sweating; then hot, dry, red skin; high fever; vomiting; confusion; seizures during cooling; and unconsciousness. The blood pressure may be low or high, and lack of sweating is also common, though athletes may perspire. The body temperature often will be 105 degrees or higher. The Pennsylvania Medical Society advises immediate treatment if any of these symptoms are present. "After calling 911," Dr. Heine says, "move the victim to a cooler location, remove heavy clothing, fan the body and wet it down with a cool sponge or cloth, and encourage the individual to drink cool fluids."