Goose bumps

Goose bumps, goosebumps or goose-pimples (also called chill bumps) are the bumps on a person's skin at the base of body hairs which may involuntarily develop when a person is tickled, cold or experiencing strong emotions such as fear, euphoria or sexual arousal.

The formation of goose bumps in humans under stress is considered to be a vestigial reflex. Its function in other apes is to raise the body's hair, and would have made human ancestors appear larger to scare off predators or to increase the amount of air trapped in the fur to make it more insulating. The reflex of producing goose bumps is known as piloerection or the pilomotor reflex, or, more traditionally, horripilation. It occurs in many mammals; a prominent example is porcupines, which raise their quills when threatened, or sea otters when they encounter sharks or other predators.