A chemical that lies to your nerves
Why Are Some Peppers Hot?
A chilli is not actually hot. It contains a chemical that switches on the nerve that reports heat.
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Step 1 of 5
You have a nerve that reports hot things.
A particular sensor in your mouth and skin fires when the temperature goes above about forty-two degrees. Its message means danger, and your brain reads it as burning.
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Step 2 of 5
The chilli chemical fits that sensor.
By coincidence of shape, it locks onto the same sensor and switches it on directly. Everything downstream is identical to a real burn, so it feels like one.
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Step 3 of 5
Water does not help.
It is not about cold. It is about what the chemical dissolves into. The chemical is oily and does not dissolve in water, so a glass of it just moves it around. Milk and yoghurt carry fat, which does dissolve it and take it away.
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Step 4 of 5
The plant is aiming at mammals, not birds.
A mammal chews the seeds and destroys them; a bird swallows them whole and spreads them. Birds lack that sensor entirely, so a chilli is hot to us and not to them.
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Step 5 of 5
Heat is measured by dilution.
The old scale asked how much sugar water it takes to dilute an extract until nobody can taste the burn. A sweet pepper needs none; the hottest need over a million times their volume.
Repeated exposure genuinely wears the sensor down, which is why people who eat chilli often can take far more of it.
The short version
Chilli heat is a chemical that opens the nerve for high temperature, so the burn is a real signal about nothing.
Try it yourself
After something spicy, try water and then milk. Only one of them does anything.