The integumentary system of the upper torso is made up of the skin and its appendages (such as the hair); its primary function is to protect the body from damage; it is also involved in temperature regulation and in the sense of touch. Upon exposure to sunlight, the integumentary system is also the primary vehicle for synthesis of vitamin D.
The integumentary system of the upper abdomen includes the skin and hair of this region; the skin of this system protects against damage to the organs contained within the abdomen. While both men and women have hair on their chests, this hair is usually quite fine on most women and may be nonexistent. Men typically have much thicker hair on their chests than women, and are also much more likely to have visible hair on their backs.