Extreme heat makes it especially hard for your body to cool down, so you need to be extra careful if you exercise or play sports when it's baking outside.
Your brain tries to keep your body within a degree or two of 98.6 degrees Fahrenheit 37 degrees Celsius, and it does so in part by triggering sweat. When sweat dries, it carries away heat from your body's surface.
When sweat can't do its job - because your body is generating a lot of heat or it's too hot and humid to cool down - you are at risk of becoming dehydrated or even getting a heat-related illness such as heat exhaustion or heat stroke .
When heat is dangerous - and why humidity matters
The higher the temperature, the harder it is for the body to stay cool, but humidity plays a big role too. High humidity makes it feel hotter than the temperature because it makes sweating less effective. There's so much water in the air already that it can't take up much more - including the water in your sweat.