So you're eating an apple or some chips, and then all of a sudden you crunch on something that is not your food. Whether it's your lip or your cheeks, it hurts like hell. It's not like we forget how to chew, so what's going on when you bite your lip or cheek?
There are a couple different reasons as to why this happens, so let's get started!
As you chew, your teeth are rubbing up and down against your lips and cheeks. As humans evolved, we developed methods to stop ourselves from biting our tongues, lips, and cheeks, and one of those methods is saliva. Natural lubrication is produced to help your teeth easily slide up and down the inside of your mouth.
However, oily and dry foods can suck the moisture from your mouth and cause a higher chance of biting down on something you didn't want to. Bread is inherently dry and absorbs a lot of moisture, so it forces your mouth to produce saliva in overdrive. Oily foods, like pizza, are hydrophobic, meaning it essentially repels water.
You can prevent dry mouth by drinking water before you eat a dry or oily meal, and also avoiding these types of food if you find yourself biting the inside of your mouth too often.
But lack of moisture is not the only reason people bite their lips and cheeks.