Hans House, M.D., a physician in the Emergency Treatment Center at University of Iowa Hospitals and Clinics, says hot weather can cause a variety of health problems, including dehydration, heat exhaustion, and heat stroke.

"Extreme heat is especially hazardous to the very young and the elderly who have less ability to compensate for the temperature," says House. "They may not be able to get out of the heat or may be on medications that interfere with the body's regulatory systems."

Heat is also a problem to those with chronic illnesses, such as heart disease, diabetes, and lung problems, due to the increased stress on the body.

Heat exhaustion occurs when someone becomes dehydrated from being exposed to hot weather for too long and develops symptoms.

Typically, House says, someone suffering from heat exhaustion will report fatigue, weakness, dizziness, and nausea and vomiting. They may also have a headache or muscle cramps. "Basically, if you start feeling sick from being in the heat, you probably have some degree of heat exhaustion," he says.

The key difference between heat exhaustion and heat stroke is the presence of mental status changes. "Heat stroke is a complete break-down of the body's ability to compensate for heat, and the body temperature continues to rise unheeded, with disastrous results," says House.

"Elevated body temperature with a LACK OF SWEAT, and changes in mentation, such as confusion, bizarre behavior, seizures, or coma are symptoms of heat stroke.

"With heat exhaustion, there is still time to get out of the heat, drink lots of fluids, and cool off. Once confusion or other signs of heat stoke occur, the person's life is in grave danger and an ambulance must be called immediately.

"While waiting for emergency help, move the person to a shaded area, preferably inside in an air-conditioned building," says House. "Moving air across the skin will increase evaporation which helps to cool the body, so any fanning or breeze is very useful. Most important, drink plenty of fluids, and even pour some on the skin, which also helps to cool the body."

Humidity makes the summer heat worse because less evaporation from the skin can occur when the air is already so heavily laden with moisture. To avoid having problems, be aware of the heat, avoid heavy exertion in the warmest part of the day, use any type of fan to get some air movement, and seek shade or A/C when you begin to feel too warm says House.

Most important is to drink plenty of fluids and stay hydrated.

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Hans House, M.D.