The answer to whether shark skin is sharp is definitively yes, but its texture is complex. Running a hand along a shark’s body from head to tail feels smooth, like rough velvet. Stroking it in the opposite direction, from tail to head, reveals a highly abrasive, coarse surface, similar to sandpaper. This unique texture results because the skin is not covered in the flat, overlapping scales typical of most bony fish. Instead, a shark’s entire body is encased in a protective layer of tiny, tooth-like structures.
The Science Behind the Rough Texture
Shark skin is covered by specialized structures known as dermal denticles, which literally translates to “skin teeth.” These structures are classified as placoid scales, found only in cartilaginous fish like sharks, rays, and chimaeras. The denticles are structurally homologous to the shark’s own teeth, essentially forming a durable, protective armor of countless miniature teeth. Each denticle is oriented backward toward the tail, and this backward-facing orientation accounts for the dramatic difference in texture when touched in opposing directions.
Microscopic Structure of Dermal Denticles
The abrasive quality of dermal denticles lies in their specific anatomical composition, which mirrors that of a tooth. Each denticle is anchored by a broad, flat base plate embedded in the dermal layer. The main body is composed of dentine, a hard, calcified tissue providing the denticle’s bulk and strength. Surrounding the dentine is vitrodentine, an extremely hard, enamel-like substance. This vitrodentine cap forms the pointed, exposed crown, generating the sharp, rasping texture.
The central part of the denticle contains a pulp cavity supplied with a blood vessel and nerves, indicating that these structures are living and actively maintained. Historically, dried shark skin, known as shagreen, was used as a fine abrasive, similar to modern sandpaper, for polishing wood and other materials. This hard, pointed cap on millions of individual structures creates a natural, highly effective abrasive surface that is continuously renewed.
How Shark Skin Helps Them Swim
The unique structure of dermal denticles provides an evolutionary advantage beyond protection. The denticles are precisely shaped and spaced to interact with the surrounding water, significantly improving the sharkâs hydrodynamics. As the shark moves, microscopic ridges and grooves on the crowns channel water flow over the body. This channeling action reduces turbulent flow, which is the chaotic swirling of water that creates drag.
By maintaining a more organized, laminar flow close to the skin, the denticles decrease skin friction drag. This reduction allows the shark to glide through the water more efficiently, increasing speed and decreasing energy expenditure. The denticles also contribute to an anti-fouling mechanism, preventing the build-up of algae and other parasitic organisms. The denticles can slightly lift and tilt, creating a micro-turbulence that makes secure attachment difficult, which keeps the skin clean and preserves hydrodynamic efficiency.