Goose bumps

Goose bumps are small raised areas of skin produced when tiny muscles attached to hair follicles contract. Cold and strong emotions commonly trigger them.

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Arrector pili muscle: A small smooth muscle attached to a hair follicle that contracts to raise the hair and dimple the surrounding skin. Its contraction directly creates the raised skin around a follicle.
Thermoregulation: The processes by which an organism maintains its internal temperature within a viable range. Cold-triggered piloerection is one response involved in temperature regulation.
Evolution of human body hair: The evolutionary history of the distribution and density of hair on the human body. Reduced body hair helps explain why piloerection is less effective in humans than in furred mammals.
Frisson: A brief wave of pleasurable chills, often accompanied by goose bumps, triggered by music or other intense experiences. It is a familiar emotional form of goose bumps, especially during music.
Piloerection: The involuntary erection of hairs caused by contraction of arrector pili muscles. Goose bumps are the visible skin effect of this hair-raising response.
Cold exposure: Contact with environmental temperatures low enough to draw heat from the body. Cooling can activate the pilomotor reflex and produce goose bumps.
Thermal insulation: The slowing of heat transfer between an organism and its surroundings. Raised fur can trap insulating air, the likely ancestral benefit behind cold-triggered piloerection.
Aesthetic chills: Chill sensations and goose bumps elicited by emotionally powerful art, music, or other aesthetic experiences. This response shows how artistic experiences can recruit the same bodily reaction as cold.
Sympathetic nervous system: The autonomic nervous system division that mobilizes the body for rapid responses to challenges. Its signals activate the muscles that produce goose bumps.
Emotional arousal: A state of heightened psychological and physiological activation in response to emotion or stimulation. Fear, awe, and excitement can trigger goose bumps even without cold.