Pineapple is one of the most pungent fruits to snack on. Sure, lemons probably have them beat in the bitter and tart categories, but pineapples are the cause of sore tongues and lips everywhere. And there's a sudden social media storm surrounding the reason why. (Sorry HIMYM fans, this is a different Pineapple Incident.)
The irritation is caused by a combination of enzymes in pineapples called bromelian, which break down proteins and essentially attack your tongue, cheeks, and lips on contact. But once you chew and swallow it, both your saliva and stomach acids overtake them. So if your mouth hurts after eating raw pineapple, you're not alone—it happens to virtually everyone. The good news is that your tongue rebuilds those proteins and amino acids, so it won't be sore for long.
It's no secret that fruits and vegetables contain enzymes that break down proteins, fats, and carbs. That's one of the many reasons they're so great for us. Some produce, however, contains larger than average amounts of enzymes, including papayas, kiwi, grapes, figs, avocados, dates, bananas, and mangos. I mean, that's why lemon, pineapple, and other citruses are used as marinades and meat tenderizers: They divide the collagen in your steak.
Wondering why this phenomena doesn't happen when you cook the fruit or add it to pineapple desserts? Heating it, roasting it, grilling it, baking it—all of those methods cause a chemical reaction that eliminates the enzymes and we're left with sweeter, more sugary fruit.