The National Weather Service developed the heat index to help people identify days when the risk for a heat illness is higher than normal. During a heat wave, the heat index is excessive for many days in a row. Everyone has an increased risk for a heat-related illness during a heat wave.
A heat-related illness can be more serious for:
Older adults, who may not notice excessive heat, do not sweat as effectively, or do not feel thirsty.
Small children, who can't transfer heat very well.
People with chronic medical conditions.
People taking medicines, such as heart medicines or tranquilizers, for serious psychiatric disorders or depression.
People with weight problems.
People with alcohol or drug use problems.
People with mental health or developmental problems.
Other things that affect a person's risk for a heat-related illness during a heat wave include:
Living in cities, because heat is trapped by tall buildings and air pollutants.
Not having cooling devices, such as fans or air-conditioning.