piloerection

Goose bumps (in American English), goose pimples (in British English), goosebumps, or gooseflesh 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 by some to be a vestigial reflex, though visible piloerection is associated with changes in skin temperature in humans. 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.