Heatstroke is caused by prolonged exposure to high temperatures or by doing physical activity in hot weather. You are considered to have heatstroke when your body temperature reaches 104 F (40 C) or higher. High humidity, certain health problems and some medications increase your risk of heatstroke. So does being a young child or older adult.

Heatstroke is the progression of two worsening heat-related conditions. When your body overheats, you first may develop heat cramps. If you don't cool down, you may progress to symptoms of heat exhaustion, such as heavy sweating, nausea, lightheadedness and feeling faint.

Heatstroke occurs if your body temperature continues to rise. At this point, emergency treatment is needed. In a period of hours, untreated heatstroke can cause damage to your brain, heart, kidneys and muscles. These injuries get worse the longer treatment is delayed, increasing your risk of serious complications or death.

Sep. 02, 2011