When air temperature rises, the body turns on its natural cooling system - sweat. Excess heat from inside the body is pulled into the circulatory system. When the warmer blood reaches the skin, the heat is drawn into sweat. The warm sweat evaporates and the cooled blood returns to circulate once again through the body.

Prolonged or profuse sweating decreases the volume of fluid in the body, including the volume of blood. Blood pressure also decreases, which reduces the ability to move warm blood to the skin for cooling. To compensate, the heart beats faster. Eventually, like a car trying to cool a hot engine without enough radiator fluid, the body's cooling system begins to fail and the body overheats. Exercise increases the body's core temperature and can increase the risk of overheating.

There are several degrees of heat-related illnesses. Heat cramps occur when the body loses salt and moisture through sweating, leading to painful cramps in the muscles after exertion. The affected muscles are usually those in the legs, arms or abdomen. Heat exhaustion typically occurs in people who have been working or exercising in hot temperatures. Too much fluid is lost through sweating. So, as the body tries to pump more blood to the skin to reduce core temperature, blood flow to the vital organs decreases. This causes a mild form of "shock." Symptoms can include fatigue, nausea, vomiting, dizziness or headache. Patients may also have a rapid but weak pulse and rapid, shallow breathing. Heat stroke is the most serious form of heat-related illness. It occurs when the body's temperature regulating system shuts down, causing the internal body temperature to rise rapidly. The elevated temperature can quickly damage vital organs, leading to permanent disability or death. The skin may be red, hot and dry. Heart rate may be rapid and weak and breathing may be shallow. The patient may appear confused and complain of a severe headache, dizziness or nausea. This is a medical emergency. Treatment must be given immediately to prevent loss of consciousness and death.

In an average year, about 400 people in the U.S. die from heat exposure. In fact, the CDC reports from 1979 to 2003, more than 8000 Americans died from excessive heat - more than the numbers who were killed by hurricanes, lightning, tornadoes, floods and earthquakes during the same period. During a heat wave (defined as more than 48 hours of a temperature 90 degrees F or 80 percent or higher high humidity), the number of deaths greatly increases. Researchers report that the extremely hot summer of 2003 led to more than 50,000 deaths across Europe. Infants, children four and under, people 65 and older, those who are overweight, and patients with chronic health problems or taking certain medications are at highest risk for heat-related illness.

Dealing with the Heat

Health experts have several suggestions to help people deal with high temperatures and reduce their risk of developing a heat-related illness:

Drink plenty of fluids. Keep the body hydrated to replace fluid lost through sweating. Thirst is a sign that the body has already become dehydrated. So drink even if you don't feel thirsty. Water is best. Avoid drinks with alcohol or a lot of sugar, which can dehydrate the body.

Slow down. Avoid strenuous activity during the peak hours of sunlight. If you must work outside, it's best to do it early in the morning - before the temperature rises. Take frequent, regular breaks, seeking shelter in the shade whenever possible.

Pay attention to the reported "Heat Index." This is a measure that combines the actual temperature and humidity level to provide a corresponding "real-feel" temperature. The predicted heat index may be listed in the weather section of the local newspaper. The current heat index is often reported on local news.

Keep in touch with elderly neighbors, relatives and friends. Make sure they are well and they have fans or air conditioning to help them stay cool during a heat wave.

Dress for the appropriate temperature. When working outside, wear lightweight, light-colored, loose-fitting clothing (don't forget the sunscreen!). A wide hat can help protect the body from some of the sun's direct rays.

Let "Cooler" Heads Prevail

Several types of apparel items have been developed to help consumers stay cool in hot temperatures. Kevin Pringles and his mom, Linda Cook, have teamed up to form a company, called Hydro Headwear, that produces a line of "cooling" hats The hats contain acrylamide acrylate/potassium copolymer crystals, a substance that absorbs and retains water. The crystals were first developed by the agriculture industry to help maintain water in soil.

The inside of the top of the hat contains 15 water-soluble tubes of the crystals. The hat is soaked in water for about 20 minutes. The crystals absorb water, swelling to 400 times their original size and forming a gel-like substance. Even with the water absorption, the hat weighs less than a pound. The crystals also maintain the original temperature of the water for about two hours. Thus a hat soaked in ice water will feel colder than one soaked in water at room temperature.

When the hat is placed on the head, air flowing through the hat causes evaporation, cooling the head and the body. The crystals will eventually lose their water content through the evaporation process. But the hat can be soaked again to maintain the cooling effect. If the hat is allowed to dry, the crystals will eventually return to their original dry state.

The hats are currently available in several styles and are sold at some specialty stores. They will soon be available on line at http://www.chillfactorclothing.com. Cost is about $20.00. Pringles says the crystals should last a long time. In fact, he says the hat will wear out long before the crystals.

Pringles and Cook are co-owners of Hydro Headwear. The company was created last year through a grant from the Edson Student Entrepreneur Initiative at Arizona State University, which helps fund student initiatives to develop marketable ideas and products.

The hats are sold at some specialty stores and will soon be available online at:

http://www.chillfactorclothing.com

You may also call: 1-877-88-CHILL.

For general information on dealing with heat-related illnesses:

American Geriatrics Society Foundation for Health in Aging

American Red Cross

Centers for Disease Control and Prevention

FEMA

For information about the heat index:

NOAA National Weather Service Weather Forecast Office