Hair is part of the integumentary system, which is the largest organ system in the human body.

Here's why:

* Integumentary system: This system includes the skin, hair, nails, and associated glands.

* Function: The integumentary system serves multiple functions, including protection, regulation of body temperature, sensation, and excretion.

* Hair's role: Hair acts as an insulator to help regulate body temperature. It also provides protection from the sun and physical trauma.