Why chilies hurt
The heat of a chili pepper is not actually a taste. That burning feeling comes from the body’s pain response system. Capsaicin inside the pepper activates a protein in people’s cells called TRPV1. This protein’s job is to sense heat. When it does, it alerts the brain. The brain then responds by sending a jolt of pain back to the affected part of the body.
Normally, the body’s pain response helps prevent serious injury. 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.
Biting into a jalapeño pepper has the same effect on the brain as touching a hot stove. “[Peppers] trick our brain into thinking we are being burned,” says Tewksbury, who now leads the Boulder, Colo., office of Future Earth. (The group promotes research to protect Earth's resources). Pepper plants likely evolved their fake-out technique to keep certain animals from eating up their fruit, according to Tewksbury’s research.
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? It ensures the plants’ survival. 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.
People managed to outsmart the pepper when they realized that a chili’s pain doesn’t cause any lasting damage. Those with pepper allergies or stomach conditions do need to stay away from chilies. But most people can safely eat hot peppers.