The middle layer of the skin is called the dermis, which is made up of connective tissue that contains blood vessels, nerve endings, sweat glands, and hair follicles. The two main components of the dermis are adipose tissue, which helps cushion and insulate the body, and collagen fibers, which provide strength and support to the skin. The dermis also contains other types of cells, such as fibroblasts, which produce collagen and elastin, and immune cells, which help protect the body from infection.