The spiciness of spicy foods is typically found in an oil contained in the spicy food.
Bread helps absorb the spicy oil. Milk helps to neutralize it.
Being oil based, this is why drinking water doesn't help - water will just pass over the oils at best, or spread it around further at worst.
Buttered bread works really well too
Spice in foods is usually capsacin oil. Bread essentially acts like a paper towel, while milk that has a high fat content dissolve the oil.
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