The skins of most sharks are covered with placoid scales, or denticles as they are sometimes called. The placoid scales are totally different from those scales found on bony fishes, and are build up the same way as the teeth. This means that they are changed continually as the shark growth. Placoid scales derives from the epidermis unlike the scales on bony fishes that have no epidermal origin. Bony fishes does not normally change their scales like sharks, instead the scales growth and becomes larger as the fish gets older. Shark denticles between different species differs distinctively in shape and distribution, and are often a useful tool when identifying sharks.

(© J. Lokrantz/Azoteimages)

The skin of some sharks is so rough that the victim of a shark attack may have large areas of his own skin scraped off by contact with sharks body. Because of its special texture, shark skin was once used as sandpaper.