What makes chili spicy

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To your dismay, the water does almost nothing to douse the flames. Or is it? Humans have been cultivating chillies for years, but we are still learning new things about the science behind their heat and how it reacts with our body.

In the late s, scientists identified the pain nerves that detect capsaicin: the chemical in chillies responsible for most of the burn. And this explains why full-cream milk, and not water, is the traditional choice for quelling the fire. The hottest part of a chilli is not the seeds, as many people think, but the white flesh that houses the seeds, known as the placenta.

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 chillies 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 chillies deal with harmful microbes, as well as hungry mammals.

Birds, unlike mammals, are not bothered by capsaicin, and their digestive systems actually encourage chilli seeds to germinate. So when birds fly away and spread their droppings, they help the parent plant to disperse its seeds. The brain then responds by sending a jolt of pain back to the affected part of the body. If a person accidentally places fingers on a hot stove, the pain makes him or her yank that hand back quickly. The result: a minor burn, not permanent skin damage.

People, mice and other mammals feel the burn when they eat peppers. Birds do not. Why would peppers develop a way to keep mammals away but attract birds? Mammals have teeth that smash seeds, destroying them. Birds swallow pepper seeds whole. Later, when birds poop, the intact seeds land in a new place. That lets the plant spread. Those with pepper allergies or stomach conditions do need to stay away from chilies. But most people can safely eat hot peppers. Capsaicin does not actually damage the body in the same way that a hot stovetop will — at least not in small amounts.

In fact, the chemical can be used as a medicine to help relieve pain. It may seem bizarre that what causes pain might also make pain go away.

The human body is good at repairing itself, however. Eventually, the pain will fix this pain system and can once again send pain alerts to the brain. However, if the TRPV1 protein is activated often, the pain system may not get a chance to repair itself in time.

The person will only feel discomfort or burning at first. Then he or she will experience relief from other types of pain.

For example, people with arthritis Arth-RY-tis regularly have pain in their fingers, knees, hips or other joints. Rubbing a cream containing capsaicin onto the painful area may burn or sting at first. After a while, however, the area will become numb. He says other researchers are currently testing capsaicin patches or injections. These would likely do a better job at halting pain. Unfortunately, these therapies tend to hurt a lot more than a cream — at least in the beginning.

Someone who can tough out the initial discomfort, however, could get relief that lasts for weeks, not hours. Chili peppers also may help people lose weight. He works at the University of Wyoming in Laramie. As a pharmacologist, he studies the effects of medicines. His team is now working to create a drug to make the body burn through fat more quickly than usual.

A primary ingredient: capsaicin. In the body, capsaicin triggers a stress reaction known as the fight-or-flight response. It normally occurs when someone or some animal senses a threat or danger. The body responds by preparing to either run away or stand and fight. In a study, his group showed that mice that ate a high-fat diet containing capsaicin did not gain extra weight.