When it comes to spicy foods, people are very divided. Across families, marriages, friend groups, there’s usually one half who loves the feeling of eating – and subsequently digesting – something really hot, and the other half who would rather not eat at all.

And there’s good reason for this.

Ever feel the adrenaline rush when you do something that scares you and it goes, well, better than your brain might have expected? Think about the big hit when you get off of a rollercoaster, or the accidental burst of laughter when you almost fall over but manage to rectify your stance before it’s too late.

Though spicy food isn’t really a danger to us (in moderation, at least) it does cause our pain receptors to flare up, and thus causes some stress in our nervous system. Add that to some of the delicious flavors that spicy chili is usually paired with (most of us will have a hot curry, or spicy tacos rather than just eat a chili pepper on its own) and you get a recipe for some feel-good energy coursing through your veins.

But why are foods spicy to begin with? Well, when it comes to chili peppers (the most common ingredient in our spicy foods) the key factor is a chemical called capsaicin. Though many people believe that the capsaicin is found in the seeds of chili peppers – and avoid eating the seeds as a result – it’s actually most concentrated in the more white-coloured flesh that holds the seeds within the fruit.

It is the presence of capsaicin that causes pain in the body. When you eat something containing a sufficient quantity of capsaicin (and depending on your tolerance level, that amount can vary) you will find that your tongue and your mouth is burning. Sometimes even your lips burn too. As you breathe it in, or hot, spicy air fills your mouth from the food, you may find that the capsaicin starts to affect your nose and eyes, causing them to run. For some people, it even affects the lungs, making them wheeze. As it travels through your body, you may feel the capsaicin hit your stomach, and if you’re really unlucky you’ll feel the intense burn as this plant chemical exits your body, too.

Why such a dramatic reaction? Well capsaicin can actually be considered a toxin (and it is poisonous to humans in very high doses). In evolutionary terms, this chemical was in the interests of the capsaicin plants: it fended off predators, with the bright red color of the chili and its toxic kick meaning that it would be left to grow undisturbed.

A similar effect can be found in other spicy products too. For example, sichuan peppers – popularly used in food from the Sichuan region of China – contain hydroxy-alpha-sanshool. This chemical, while still having a spicy effect, feels different in the mouth and the body, causing more of a buzz than a burn. This is because the chemical causes different pain and heat receptors in the body to react, ultimately leading to a slightly different sensation – one that is no less pleasant, or unpleasant, depending on your standing on spice.

So, while eating spicy food in moderation and up to your own tolerance is absolutely fine – and an exciting experience for some – it’s absolutely okay if you don’t like your food to come with a burning tongue, a runny nose, and stomach pain. And now you have a perfectly viable excuse – evolution – to back you up.

If you think that’s impressive, check out this story about a “goldmine” of lithium that was found in the U.S. that could completely change the EV battery game.