It's summer. The sun is shining, temperatures are rising, and the air is a hot, sticky mess. That steamy feeling that washes over you when you step outside is caused by humidity in the air. And it can wreak havoc on your body.

To understand how humidity affects the human body, you need to understand how the body responds to heat. As you probably already know, your body reacts to high temperatures by releasing sweat. But sweating only works if the moisture on your skin actually evaporates. When the humidity is high, the air is already loaded with moisture, reducing its ability to absorb the sweat from your skin.

Think of the air like a sponge. When humidity is low, that sponge can absorb plenty of water. But when it's very humid, the sponge may be nearly saturated and unable absorb any more. So you're sweating like crazy but not getting cooler.

As your internal temperature continues to rise, your body responds by cranking out even more sweat, leaving you feeling hot, sticky and in danger of dehydration. With all that sweat being pumped out, your body is losing water, salt and minerals.

High levels of humidity make the temperature feel even hotter than it really is because the moisture in the air makes it difficult for our bodies to cool down. Just as meteorologists tell us the wind chill in winter to describe how the temperature really feels when winter winds are blowing, they use the heat index to describe how high temps feel when the humidity rises.

When the humidity is 30 percent or below, the air temperature feels more or less like what you see on the thermometer. The chart below from the National Weather Service, however, shows how those temperatures skyrocket as the humidity rises. That's why a hot 90-degree Fahrenheit day (32 degrees Celsius) feels like an unbearable 105 degrees Fahrenheit (40 Celsius) when the humidity is 70 percent. It feels even hotter as the humidity rises.

Heat Index Chart This chart from the National Weather Service shows why it feels so hot when the humidity rises. (Image: weather.gov)

If all that isn't enough to leave you feeling exhausted, humidity can also affect your sinuses, as high humidity often encourages dust mites and mold. If you hide indoors to escape, you could be exposing yourself to excessive levels of allergens that leave you feeling headachey and fatigued.

So what can you do to combat the effects of humidity on your body? On hot summer days, keep track of the humidity just as you would the temperature. When it's high, be sure to drink plenty of water, slow down and rest as often as possible to give your body a chance to cool down and recover.

Why does humidity make you feel so awful?
Here's what these steamy days are doing to your body.