Piloerection

Piloerection'Bold text, popularly known in humans as Goose bumps, also called goose pimples, goose flesh, chill bumps, chicken skin, or the medical term cutis anserina', are the bumps on a person's skin at the base of body hairs which involuntarily develop when a person is cold or experiences strong emotions such as fear or awe, or captures the essence of a unique experience. The reflex is known as horripilation, piloerection, or the pilomotor reflex. It occurs not only in humans but also in many other mammals; a prominent example are porcupines which raise their quills when threatened.

Goose bumps are created when tiny muscles at the base of each hair, known as arrectores pilorum, contract and pull the hair erect. The reflex is started by the sympathetic nervous system, which is in general responsible for many fight-or-flight responses.

The reflex is often a response to cold: in animals covered with fur or hair, the erect hairs trap air to create a layer of insulation. It can also be a response to anger or fear: the erect hairs make the animal appear larger, in order to intimidate enemies. This can be observed in the intimidation displays of chimpanzees, in stressed mice and rats, and in frightened cats. In humans, it can even extend to piloerection as a reaction to hearing nails scratch on a chalkboard or listening to awe-inspiring music.

Piloerection as a response to cold or fear is vestigial in humans; as humans retain only very little body hair, the reflex (in humans) now serves no known purpose.

In humans, goose bumps are strongest on the forearms, but also occur on the legs, back, and other areas of the skin that have hair. In some people, they even occur in the face or on the head.

Piloerection is also a (rare) symptom of some diseases, such as temporal lobe epilepsy, some brain tumors, and autonomic hyperreflexia. Goose bumps can also be caused by heroin withdrawal. A skin condition that mimics goose bumps in appearance is keratosis pilaris.

Goose bumps can occur only in mammals, since other animals do not have hair. The term "goose bumps" is therefore misleading: the bumps on the skin of a plucked goose technically do not qualify as piloerection even though this is where the term comes from. Birds do however have a similar reflex of raising their feathers in order to keep warm.

The Latin horere is the root of words such as "horrific" or "horror"; it means "to tremble".

In other languages, the "goose" may be replaced by other kinds of poultry. For instance, "hen" is used in French (la chair de poule), Dutch (kippenvel), Spanish (la piel de gallina), Chinese (雞皮疙瘩) and Afrikaans (hoendervleis).