My question is about taste: why can some people tolerate chilli and some not? Chilli tolerance seems to improve when you eat more, but what’s happening in your mouth and brain? – Andrew Beale
The perception of taste is much more complicated than most people assume at first. When you bite into an apple, for instance, there is a lot going on. Even before your tongue gets a hold of that first bite, your emotional state, social circumstance, the way the apple was presented, and your perception of its value will all affect your experience of the apple. Once it’s inside your mouth, receptors on your tongue will react according to the presence of sugars (sweetness), acids (sourness), metal ions (saltiness), a complicated set of chemicals that I won’t get into here (bitterness), and amino acids (umami) to give a basic perception of taste. Through the trigeminal nerve, your tongue will also send information to your brain about the temperature and texture.
In order to truly appreciate the flavour (not just the taste and physical properties), your nose needs to get in on the action. In fact, the only way you’ll know that you’ve eaten an apple and not a pear is that a bundle of nerves at the back of your nasal passage will react to all of the various volatile compounds in the fruit that have floated up through a hole in your palate. You can even try this at home. Plug your nose and take a bite of an apple or a pear, you won’t be able to tell the difference because the two fruits share almost every attribute that your tongue can decipher. In this instance, it’s all up to your nose.
I know that doesn’t answer your question directly, but I think the intricate process of perceiving tastes and flavours is a fascinating and often under-appreciated topic.
The particular sensation you’re asking about, spiciness, is the result of the interaction of the chemical capsaicin with your tongue. Capsaicin is commonly found in the fruits of the Capsicum genus of plants and it tricks your tongue into sending a “hot” signal to your brain. So when people say that spicy food is “hot”, their brains are literally interpreting the food as temperature-hot regardless of the actual temperature of the food.
There is significant variation between people in terms of their tolerance for foods with capsaicin (like chilis). This tolerance seems to be largely a cultural phenomenon, with people who grew up eating spicy foods being desensitized to it. Some have argued that people with thrill-seeking personalities tend to prefer spicy foods and that there is an allure to foods that our senses tell us are dangerous but that we know aren’t. A study from the 90s showed that the same dose of capsaicin applied directly to the tongue every minute will increase sensitivity, but as soon as you have a break (as short as 2.5-5 minutes), your tongue will become desensitized and you’ll be able to handle more heat. Apparently if you repeat this process every day for a whole childhood, the nerve endings that react to capsaicin will die off.
So it turns out that spice tolerance is a combination of nature and nurture, as are most things in life. Over enough exposures, your tongue gets desensitized and either stops sending panic signals to your brain or your brain stops listening to those panic signals. According to this 2012 study, however, habitual spicy food eaters were more sensitive to actual hot water than spice-avoiders. This, combined with the finding that spice-lovers are better able to determine gradations of spice, may indicate that a spice-lover’s tongue actually becomes more sensitive but won’t set off pain alarms as easily.
Exactly what is going on remains a mystery, but biological predisposition, culture, and personality are all playing a role.
If you’re interested in boosting your spice tolerance, check out this article that has some great advice for spice novices.