Brian (a different Brian) asked via Twitter:

嗨，布莱恩，

There are all sorts of foods that irritate the senses, and we love many of those irritants. Usually, when people talk about spicy food, though, they’re talking about chills. The class of chemicals responsible for a chili’s spiciness are capsaicins.

首先，为什么：辣椒是水果，水果通常会邀请自己吃东西，以便让动物吃它们。这些动物将种子待一会儿，最终以通常的方式摆脱了种子。时间过去了，种子将其营养丰富的环境带入植物。这是一种令人印象深刻的进化策略。

Chili seeds, unlike many fruit seeds, are destroyed by the high acid content of mammal stomaches. In order to combat the destruction of potential new plants, chili peppers evolved the ability to generate capsaicins which irritate the taste buds of mammals. In situations where it’s harder to grow, such as dry temperatures, the spiciness is concentrated even more.

So how do chilis spread their seeds? Bird stomaches don’t harm the seeds, and birds can’t taste capsaicin, so no problems there. Birds eat the chili peppers, fly away, drop the seeds after a while, and the circle of life continues.

So, back to the main question, which is: how does this work? Molecules work in two ways. The first is kind of a magnetic attraction, based on the number of electrons available to the atoms. I don’t think we want to go into the details right now, but the short of it is that some atoms will stick to other atoms really well, while other atoms completely ignore the space.

The second way molecules, especially proteins, work is by shape. Wetalked about this a bit in Freezer Burn，但本质上，分子会在其中有这些原子等待匹配的原子出现，但是分子本身可以在各种疯狂的形状中。蛋白质一直根据温度或物理搅动或许多外部力量而改变形状。当您做饭时，您常常不重塑这些蛋白质，并将可用原子暴露于可以以正确方式单击的其他原子。

Spicy Peanut Noodles with Ground Pork & Shredded Vegetables		Beef Enchiladas with Salsa Verde		辣鸡肉和白豆辣椒

Some nerve cells have what is called a vanilloid receptor, and this receptor is one of the things that capsaicin is specially shaped to attach to. Once it does, it activates that nerve intensely, which is interpreted as heat and pain and a little bit itching, depending on the nerve and probably the variety of capsaicin. The capsaicin is also surrounded by oil, so that it’s really hard to wash off of you when it touches your skin, tongue, or eye.

Because the capsaicin is so intense when it activates the nerve, the nerve gets kind of worn out. This is why, if you eat a lot of spicy food, you become desensitized to it. Eventually the nerves recover, so if you stop eating spicy food after a while, you will lose your ability to tolerate it, until you beat down the nerve cells again.

辣椒素使热和疼痛受体脱敏的能力对于患有各种慢性疼痛的人确实很方便。实际上，辣椒素有各种医疗用途，科学家一直在发现更多的医疗用途。