What is the primary function of hair follicles?

The primary function of hair follicles is to produce hair and provide sensory input. Hair follicles are complex structures located in the dermis of the skin, and they are responsible for the growth of hair strands, which are composed mainly of a protein called keratin. Each hair follicle is associated with a small muscle called the arrector pili, which can contract to cause "goosebumps," aiding in the sensory function.

Additionally, hair follicles serve as sensory receptors that detect environmental changes. The nerve endings around the follicles make them sensitive to touch, allowing the body to respond quickly to various stimuli. This sensory feedback is important for protection against external forces.

While other functions mentioned in the choices have significant roles in skin health and body regulation, they are not the primary roles of hair follicles. For instance, absorption of sunlight and the synthesis of vitamin D are more closely related to skin cells, specifically keratinocytes, in response to UV exposure, and temperature regulation involves multiple mechanisms across the skin, including sweat glands and blood vessel activity.