This article is about the bumps that form on skin. For the book series by R. L. Stine., see Goosebumps.

Goose bumps (AE), also called goose pimples, goose flesh (BE), or cutis anserina, are the bumps on a person's skin at the base of body hairs, 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; a prominent example are porcupines which raise their quills when threatened.

Goose bumps are created when tiny muscles at the base of each hair -- called erector pilae -- 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.

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.

In humans, goose bumps are strongest on the forearms, but also occur on the legs, back and other areas of the skin that has 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 only occur in mammals, since other animals don't have hair. The term "goose bumps" is therefore misleading: the bumps on the skin of a plucked goose technically do not qualify as piloerection. Birds do however have a similar reflex of raising their feathers in order to keep warm.

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.

A skin condition that mimics goose bumps in appearance is known as keratosis pilaris.