What causes goosebumps?

Question

I know it usually happens when it's cold or whatever, but how do they form?

Answer 1

You've had goose bumps surely, haven't you? But how do you get goose bumps?

Goose bumps are a temporary local change in the skin. The chain of events leading to this skin change starts with a stimulus such as cold or fear. That stimulus causes a nerve discharge from an involuntary portion of the nervous system called the sympathetic nervous system. The nerve discharge causes contraction of little muscles called the arrectores pilorum (the hair erector muscles). Contraction of these muscles elevates the hair follicles above the rest of the skin. And it is these tiny elevations we perceive as goose bumps.

Answer 2

Goosebumps are the result of a common but benign disease, in which microscopic "goose-like" organisms (hence the name, goosebumps) find their way underneath the topmost layer of the epidermis.  They normally enter through the hair follicle, and as they migrate through the epidermis they deposit small capsules of connective-tissue-like fibers at the base of the hair follicle.  Scientists are still unsure as to the purpose of these capsules, but as of now they have been deemed relatively harmless. You experience goosebumps when increased heart rate (which often causes small fluctuations in blood circulation in the small capillaries near the surface of the skin) stimulates the small capsules to temporarily enlarge.

Answer 3

It's a vestigial trait left to us by our ancestors.

Goosebumps are created when the pilii erector (sp?) muscles in the skin raise the hairs on our bodies. This was useful for our ancestors because raising the body hair helped them keep warm and also made them look bigger to better ward off would-be predators. So when we are cold or scared, the pilii erector muscles raise the tiny hairs on our skin as a trait passed down by our evolutionary heritage