What happens to the body when the arrector pili muscle contracts?

When the arrector pili muscle contracts, it causes the hair follicles to pull upwards, resulting in the phenomenon commonly known as goosebumps. This reaction typically occurs in response to cold temperatures or emotional stimuli, such as fear or excitement. The contraction of the arrector pili muscle raises the hair, creating small bumps on the skin surface. This reflexive mechanism is a remnant from our evolutionary past when enhanced body insulation was necessary, and it can also serve as a way to make an individual appear larger in the face of a threat.

While perspiration may be involved in thermoregulation, it is not directly related to the action of the arrector pili muscles. Similarly, body temperature fluctuations or body fat changes are not direct consequences of this muscle's contraction. The primary and most visible outcome of this activity is the formation of goosebumps.