The term WHERE HAIR ROOTS GROW can be summarized as the SCALP, which is an area of skin on the head that contains the roots of hair follicles. The SCALP is composed of five layers of skin and is highly vascularized, meaning it has a large number of blood vessels. It is also rich in nerve endings, making it sensitive to touch. The SCALP is important for protecting the skull from injury and providing insulation against heat loss.