Chili Peppers Burn Your Mouth and Wasabi Burns Your Nose Because Their Heat Molecules Are Different Sizes
Spiciness is not a taste at all, but a pain alarm that mistakes large, lingering molecules and small, floating ones for real heat.
TED-Ed · The science of spiciness - Rose EvelethBite into a chili pepper and the fire sits on your tongue. Taste wasabi and the sting shoots up into your nose. The difference comes down to size.
Spiciness is not a taste like sweet, salty, or sour. It is pain. Certain plant chemicals switch on pain-sensing nerve endings in the mouth and nose, the same endings that respond to dangerously hot heat.
In chili peppers and black pepper, the chemicals responsible are capsaicin and piperine. They are part of a family of relatively large, heavy molecules called alkylamides, bulky heat compounds that mostly stay where they land, in the mouth.
Mustard, horseradish, and wasabi work differently. Their heat comes from a family of much smaller, lighter molecules called isothiocyanates. Small enough to drift easily, they float up from the mouth into the sinuses.
Your brain cannot tell these chemical alarms apart from an actual burn. Convinced you have touched something dangerously hot, it orders the standard emergency response, sweating and a faster heartbeat, the beginning of fight or flight. Size decides the battlefield, but the brain sounds the same fire alarm either way.
Questions people ask
Does drinking milk really help a chili burn more than water?
Yes. Capsaicin does not dissolve well in water, so water mostly spreads it around. Casein, a protein in milk, and fats in milk, yogurt, and ice cream can surround the oily molecules and wash them away from the pain receptors.
Why does a wasabi burn fade faster than a chili burn?
It usually does. The small wasabi molecules float into the sinuses, cause a sharp sting, and then clear out quickly. The larger chili molecules cling to the mouth and keep triggering the pain receptors longer.
If nothing is actually burning, can spicy food hurt you?
For most healthy people, no, in normal food amounts. The brain thinks there is burning, with sweating and a racing heart, but there is no hot object injuring the tissue. Extremely concentrated extracts can injure skin, eyes, and airways, so they should be treated with care.