Humans have been cultivating chilli as food for 6,000 years, but we are still learning new things about the science behind their heat and how it reacts with our body. In the late 1990s, scientists identified the pain nerves that detect capsaicin: the chemical in chilli responsible for most of the burning sensation in our mouth. But it's only during the last few years that scientists have also learnt why chilli evolved to be spicy in the first place, and they have managed to cultivate new varieties that are up to 300 times hotter than the common jalapeno.

The hottest part of chilli is not the seeds, as many people think, but the white flesh that houses the seeds, known as the placenta. But why did chilli evolve to be hot in the first place? Most scientists believe capsaicin acts mainly as a deterrent against would-be mammal predators such as rodents. But recent research suggests this may not be the whole story. US scientists working in Bolivia have studied how hot and mild chilli differ in their susceptibility to a certain harmful fungus. It turns out that the hotter the chilli, the better its defences against the fungus, leading the researchers to propose that heat may have evolved to help chilli deal with harmful microbes, as well as hungry mammals.