Goose bumps, also called goose flesh, chill bumps, chicken skin, people bumps, 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. The reflex of producing goose bumps 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.
The German word is a mimicry of English, referring to is as Gänsehaut, i.e. "goose skin", as it is in Italian (la pelle d'oca) . In other languages, however, the "goose" may be replaced by other kinds of poultry. For instance, "hen" is used in French (la chair de poule) and Spanish (la piel de gallina), "Chicken" is used in Dutch (kippenvel), Chinese (雞皮疙瘩) and Afrikaans (hoendervleis). The equivalent Japanese term, 鳥肌, torihada, translates literally as "bird skin".
As 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 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 provides no known benefit.
In humans, goose bumps are strongest on the forearms, but also occur on the legs, neck, and other areas of the skin that have hair. In some people, they even occur in the face or on the head. In humans, the areolas of the breasts of females typically show piloerection because of hormonal distribution, for example, when aroused or inside the maternity cycle.
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 withdrawal from opiates such as heroin. A skin condition that mimics goose bumps in appearance is keratosis pilaris.