What causes goosebumps when cold?

Goosebumps, also known as piloerection, occur when the arrector pili muscles contract in response to cold temperatures or emotional stimuli. These small smooth muscles are located at the base of hair follicles. When they contract, they pull the hair follicles upward, causing the hairs to stand on end, which results in the skin forming small bumps. This reaction is part of the body's natural response to cold, aiming to create an insulating layer of air to help conserve heat.

While dermal papillae contribute to the overall structure and function of the skin, they are not responsible for the generation of goosebumps. Hair follicle expansion does not directly relate to the mechanism behind goosebumps; it’s the contraction of the arrector pili muscle that drives this effect. Skin tightening may occur in various situations but is not involved in the physiological process of developing goosebumps in response to cold. This understanding of the role of the arrector pili muscle clarifies why it is identified as the correct cause of goosebumps when exposed to cold temperatures.