Hyperthermia is the general name given to a variety of heat-related illnesses. Warm weather and outdoor activity go hand in hand. However, it is important for older people to take action to avoid the severe health problems often caused by hot weather. Regardless of extreme weather conditions, the healthy human body keeps a steady temperature of 98.6 degrees Fahrenheit. In hot weather or during vigorous activity, the body perspires. As this perspiration evaporates from the skin, the body is cooled. The two most common forms of hyperthermia are heat exhaustion and heat stroke. Of the two, heat stroke is especially dangerous and requires immediate medical attention. Heat stress occurs when a strain is placed on the body as a result of hot weather. Heat fatigue is a feeling of weakness brought on by high outdoor temperature. Symptoms include cool, moist skin and a weakened pulse. The person many feel faint. Heat syncope is a sudden dizziness experienced after exercising in the heat. The skin appears pale and sweaty but is generally moist and cool. The pulse is weakened and the heart rate is usually rapid. Body temperature is normal.