What part of organ system that the hair belong?

The hair belongs to the integumentary system.

The integumentary system is the organ system that protects the body from the external environment. The skin, hair, nails, and sweat glands are all part of the integumentary system. The skin is the outermost layer of the integumentary system and is composed of several layers of cells. The skin provides a barrier against infection, UV radiation, and dehydration. The hair helps to insulate the body and protect it from the sun. The nails help to protect the fingertips and toes. The sweat glands help to regulate body temperature.