The arrector pili muscle (plural: Musculi arrectores pilorum) is a small, smooth muscle that is associated with each Hair follicles It is connected to the human body. The main function of this muscle is to raise the hair, a reaction commonly known as "goosebumps" or, medically, as piloerection. This reaction typically occurs in response to cold, fear, or various emotional states and originally served to increase the insulating properties of fur in animals or to make them appear larger than they are to deter predators.
Each arrector pili muscle is attached to the base of a hair follicle and extends to the superficial layer of the dermis (the middle layer of skin). When contracted, the muscle pulls the hair follicle upwards, causing the hair to stand on end and resulting in goosebumps.
Although the arrector pili muscles have no direct clinical significance, they are part of studies on skin physiology and can be considered in dermatology when investigating skin reactions and conditions. Their activity may also be relevant in cosmetic and therapeutic research, particularly in relation to skin texture and hair follicle function.
In modern human physiology, the function of the arrector pili muscle is largely vestigial, meaning it has lost importance over the course of evolution, as humans have less body hair than many of their animal relatives. Nevertheless, the goosebump response remains a fascinating example of the complex interactions between the nervous system and the skin.
