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.
A heat index is listed 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:
27°C (80°F) to
32°C (89°F) may cause
32°C (90°F) to 40°C (104°F) may
cause heat cramps or heat exhaustion.
41°C (105°F) to
54°C (129°F) may cause
heat cramps or heat exhaustion, and heatstroke is
54°C (130°F) 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