Brace yourselves—cold and flu season is upon us. And when it hits you, your body will be subject to a unique form of torture: One minute you’re piling blankets upon yourself, and the next minute you’re so hot you want to go walk outside and sit in the snow (don't actually do this).

How can our bodies go to such extremes in such a short time span? Rest assured, this horrible hot-and-cold routine means your system is doing exactly what it should to fight off infection.

Bacteria and viruses thrive at 98.6 degrees Fahrenheit. When you run a fever, that’s your body essentially trying to burn off the sickness—your hypothalamus kicks into gear and raises your internal temperature in an effort to stop the virus and bacteria from growing.

That’s when the chills come in. Your system has “set” your internal temperature at a higher level, so your body is hustling to match it. It’s kind of like your house thermostat working hard to meet a warmer setting. Because you’ve reset what your internal temperature should be, the rest of you feels cold by comparison. And then, since your body thinks you’re cold, it starts shivering to try to warm you up.