Prolonged exposure to extreme heat taxes the human body beyond its abilities to function properly and can cause sunstroke, heat cramps and heat exhaustion. It can also exacerbate existing health conditions such as heart or respiratory problems. Children, infants, and the elderly are especially susceptible to heat.
Extreme heat occurs when an air mass stalls over a region.
The temperature and often the humidity build to unhealthy levels for days on end, explains the National Weather Service. Humidity reduces your body's natural cooling mechanism, the evaporation of moisture or sweat from your skin. Thus, the higher the humidity, the hotter a temperature feels to your body. City residents are particularly vulnerable to high heat conditions. When strong sunlight hits brick and stone, surfaces warm to temperatures even higher than the air.