Why do chilli peppers make your mouth feel like it’s burning?

This question was asked by Ariadne from Alexandroupoli, Greece. 

Chilli peppers have been cultivated by humans for more than 6,000 years and are used worldwide in cooking. They’re well-known for adding flavour and spice to a meal, but they can also make your mouth feel like it’s on fire. This is because of a compound in chilli peppers called capsaicin (pronounced cap-say-sin). Mostly found in the seeds and the immediate area surrounding them, capsaicin activates the same nerve cells in the mouth that register heat. This is why it feels like your mouth is burning, because the nerves are telling your brain that you’re in pain due to excessive heat. Interestingly, eating chilli peppers also releases endorphins, the chemicals in the brain that make you feel happy or excited.

So what’s the best way to counteract the burning sensation? Interestingly capsaicin is hydrophobic, which means that it doesn’t dissolve in water. So drinking a glass of water won’t really help remove it from your tongue and mouth. But liquids that are high in fats, like cooking oils and full-fat mammal’s milk, will bind to the capsaicin and wash it away. It has to be mammal’s milk though because it’s a protein called casein that’s key here. Plant derived milks like coconut milk or soya milk don’t contain casein so won’t be much more help than water!

(Image: Lucas Cobb).
(Image: Lucas Cobb).

The heat or spiciness of chilli peppers is measured on something called the Scoville scale. Invented by Wilbur Scoville in 1912, it was originally based on the reactions of volunteers after tasting each chilli but these days science has stepped in with something called high performance liquid chromatography (a way of measuring how much of something is present in a substance). Each type of chilli is given a score in Scoville units. Ordinary bell peppers, for example, have a score of 0 Scoville units; jalapeño peppers range from 3,500 to 8,000 Scoville units. Cayenne peppers have a score ranging from 30,000 to 50,000 Scovilles.

The hottest curry in the world is believed to be one called “The Widower” and measures an astounding 6,000,000 (yes, that’s 6 million) Scovilles. That’s ten thousand times stronger than Tabasco sauce. Chefs who prepare it have to wear protective goggles and face masks, and the effect of the curry is so intense that it’s thought to cause hallucinations.

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