Hair is present on more than 80% of the skin's surface. Each hair develops from a group of epidermal cells at the base of a tube-like depression called a hair follicle. This follicle extends from the surface into the dermis and may pass into the subcutaneous layer. The epidermal cells at the base receive nourishment from dermal blood vessels, which occur in a projection of connective tissue at the base of the follicle. As these cells divide and grow, older cells are pushed toward the surface. The cells that move upward and away form their nutrient supply become keratinized and die. Their remains constitute the shaft of a developing hair. In other words, hair is composed of a complex array of dead epidermal cells.