You know when you feel chilly, but you don't necessarily want to broadcast that information to everyone who sees you. Yet that is what happens when you get little bumps on the surface of your skin when you're cold. Those bumps -- called goose bumps, goose pimples or turkey flesh -- are the visible sign of an involuntary reaction.
Description
Goose bumps are so known because of their resemblance to freshly plucked poultry. The tiny bumps that pop up in reaction to cold temperatures are colorless with a hair standing straight up in the middle.
Cause
Muscle contractions cause goose bumps, according to George A. Bubenik in the "Scientific American." Each hair shaft on your body is attached to a tiny muscle called the arrector pilorum. When that muscle contracts, it causes a slight dimpling, or dent, in the skin, which causes the surrounding area to appear raised -- the visible bumps. The protrusion causes the hair to stand.
Process
The sympathetic nervous system controls the goose bump process. Cold temperatures cause the arrector pylori muscles to contract involuntarily. The tiny muscles are positioned at an angle between the hair root and the surface of the skin, extending from the follicle to the skin surface. As the muscles contract, they cause the skin to dimple and look bumpy.
Triggers
Goose bumps are triggered by the adrenal glands. Adrenaline, the stress hormone that prepares the body for the "flight-or-fight" response, is responsible for the reaction. Cold, fear, extreme stress or other intense emotions can trigger the release of adrenalin. The response is so strong that even years later, recalling an event linked to strong emotions -- either positive or negative -- can stimulate goose bumps.
Animal Link
The response that triggers goose bumps and raised hair occurs in animals, where it has a more obvious benefit. In animals with heavy coats, having the hair stand up allows for a thicker layer of insulating air, helping to keep the animal warm, says Bubenik in "Scientific American." Animals also use raised hair to make themselves appear larger when they feel threatened.
