What is the arrector pili muscle responsible for?

The arrector pili muscle is a tiny muscle located at the base of hair follicles in the skin. Its primary function is to contract in response to certain stimuli, such as cold temperatures or emotional responses (like fear), which results in the hair standing upright and the formation of what we commonly refer to as “goosebumps.” This reaction is part of the body's physiological response to help trap a layer of air for insulation or make the individual appear larger in front of a threat.

While growth of hair, detection of pain, and synchronization of hair growth are important aspects of hair and skin biology, they are not functions of the arrector pili muscle itself. Hair growth is controlled by different factors including hormonal activity and the hair follicle's life cycle. Pain detection is managed by sensory nerve endings in the skin, rather than by the arrector pili muscle. Therefore, the muscle’s role is specifically linked to causing goosebumps, making that the correct choice in this context.