The heat index provides information about how hot it feels
outside in the shade. It is a measure of the air temperature in relation to the
relative humidity for a particular day.
The National Weather
Service lists a heat index each day in the newspaper to alert people of the
risk for a heat-related illness. Direct exposure to the sun can increase the
risk for a heat-related illness on days when the heat index is high. Babies, older adults, or anyone with a health condition may have more risk of problems with the heat because of their age and general health.
A heat index of:
80°F (27°C) to
89°F (32°C) may cause
90°F (32°C) to 104°F (40°C) may
cause heat cramps or heat exhaustion.
105°F (41°C) to
129°F (54°C) may cause
heat cramps or heat exhaustion, and heatstroke is
130°F (54°C) or higher may cause heatstroke.
Prevention measures during days of high heat index will
help reduce the risk of a heat-related illness. When the outdoor humidity is
greater than 75%, losing body heat by sweating is not as effective, so other
measures to keep cool are needed.
William H. Blahd, Jr., MD, FACEP - Emergency Medicine & H. Michael O'Connor, MD - Emergency Medicine
How this information was developed to help you make better health decisions.
The Health Encyclopedia contains general health information. Not all treatments or services described are covered benefits for Kaiser Permanente members or offered as services by Kaiser Permanente. For a list of covered benefits, please refer to your Evidence of Coverage or Summary Plan Description. For recommended treatments, please consult with your health care provider.