Nails are made of a hard protein called keratin. Keratin is the same substance that makes up hair and the top layer of skin. The nail plate, which is the visible hard area of the nail from the nail root to the free edge, is mostly made of keratin and is about half a millimeter thick). The nail plate is firmly attached to the nail bed beneath it, which is the skin beneath the nail plate and is the area of the nail on which the nail plate rests. The nail bed is made of two types of tissues: the dermis and the epidermis. The epidermis is attached to the dermis by tiny longitudinal "grooves" called matrix crests). The nails start growing under the skin, and as new cells grow, they push old ones through the skin. The part of the nail that we can see consists of dead cells. The nails are linked up to a vascular environment of blood vessels, soft tissue, cellular activity, and ligaments. The nails grow slowly, with fingernails growing about 3.5 millimeters each month and toenails growing a little slower.