Your breath can be a weird thing.  

Did you ever notice that your breath is used for both its heating and cooling properties? You use your breath to cool soup, but you also use your breath to warm your hands.  

Your breath is both warm and cool!

The normal body temperature for a human is 98.6°F.  You really can't make your breath hotter than that, but you can essentially make it cooler.  

Most of how this works is how your breath comes out of your mouth. When you blow on soup, your mouth is more closed, and when you warm your hands, your mouth is usually opened wide.

You can see that there are obvious differences in what is happening when it is cold enough to see your breath.  

When you huff out a breath with your mouth open, you can see your breath. However, when you blow out a breath like you're cooling soup, you do not see your breath.

Yes, your breath is initially the same temperature when it comes out of your mouth, but how it comes out of your mouth is where there is some cool science.  

When you breathe out with your mouth wide open, you are letting out a bigger area of warm air that is the temperature of your body.  

It comes out slower than when you have your lips closer together, like when you blow on soup. That air comes out in a smaller, but faster stream, causing the cooling.

In the past, we showed you how to use a fan to cool a room more efficiently.  When you have a jet of air, like blowing on soup, you are pulling in more of the surrounding air. This is Bernoulli's principle: as the speed of a fluid, in this case air, increases, its pressure decreases.

The fast-moving air that you blow out creates an area of low pressure that causes surrounding air molecules to fill in that area of low pressure.  Those molecules are as cool as the surrounding air, causing a cooling process on the hotter things.

So, that is how your breath can be both hot and cold!