Goose bumps
Goose bumps, also called goose pimples, goose flesh, or cutis anserina, are the bumps on a person's skin at the base of body hairs (typically on the forearm), which involuntarily develop when a person is cold, afraid, or experiences other strong emotions. The reflex of producing goose pimples is known as horripilation, piloerection or the pilomotor reflex. It occurs not only in humans but also in many other mammals.
Goose bumps are created when tiny muscles at the base of each hair -- called erector pilae -- contract. The muscle pulls the hair erect. The reflex is started by the sympathetic nervous system.
Goose bumps are often a response to cold: in animals covered with fur or hair, the erect hairs trap air to create a layer of insulation. Goose bumps can also be a response to fear: the erect hairs make the animal appear larger, in order to intimidate enemies. Both of these responses are vestigial in humans: as humans have lost most of their body hair, the reflex now serves no known purpose.
Piloerection is also a (rare) symptom of some diseases, such as temporal lobe epilepsy and autonomic hyperreflexia.
The Latin horrere is the root of words such as "horrific" or "horror"; it means "to stand on end" and refers to the standing hairs of goose bumps.
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