It seems to be getting warmer each year. Extreme heat events, or heat waves, are one of the leading causes of weather-related deaths in the United States. When temperatures rise in the summer, extremely hot weather can cause sickness or even death. Heat stress is heat-related illness caused by your body's inability to cool down properly. The body normally cools itself by sweating. But under some conditions, sweating just isn't enough. In such cases, a person's body temperature rises rapidly. Very high body temperatures may damage the brain or other vital organs. Learn more: heat