In cold temperatures we bundle up with hats, scarves, and gloves, but no matter how warm we keep, the chilly winter breeze makes our nose drip. So, what is it that makes our nose run in the cold whenever we step outside? In SciShow’s latest video, "Why Do Our Noses Run in the Cold?," host Michael Aranda explains it's part biology and part physics, also known as thermodynamics.

On the biology side, our nose starts to produce more mucus to warm and moisturize all the cold, dry air, so the nasal cavity doesn't dry up, crack, and bleed. Some of the mucus drains out of our nose, in what doctors call “rhinorrhea.” This mucus dripping from our nose comes from the mucus membrane, which is a thin, protective blanket of cells that covers the inside of the nasal cavity. The mucus is mostly made of water, salt, white blood cells, and glycoproteins, or proteins that are attached to carbohydrates.

Moreover, the mucus traps particles in the air, stopping a lot of harmful stuff from getting into our lungs. Now, after we've inhaled, we end up with two warm lungs full of air, ready to be exhaled. This is where the physics component comes in.

Some of the air we inhale is water vapor, and when we exhale, it's suddenly pushed from a nice, warm environment to a harsh, cold environment. This sharp change in temperature causes the water vapor to condensate into little water droplets on the tip of the nose. This is the same way water condensates on the cold bathroom mirror while we're taking a hot shower.

Now, all of a sudden, we've got mucus and water dripping from our nose.