piloerection
n. a temporary raising of the hairs covering the surface of the skin caused by contraction of the piloerector muscles, which are attached to the individual follicles from which each hair arises. Piloerection is involuntary, being directed by the sympathetic nervous system, and elicited by cold, fear, or a startling stimulus. In mammals with a thick, visible covering of hair (e.g., cats), piloerection serves a protective function: The resulting “fluffed up” appearance makes the animal seem larger and may deter attack by others. In humans, whose skin has only a sparse covering of hair, piloerection creates a temporary roughness as the muscles pucker the surrounding skin, giving rise to such colloquial names for the effect as goose bumps, goose flesh, and goose pimples. Also called pilomotor response (or effect).