Shark skin differs significantly from the smooth, overlapping scales of most bony fish. Its surface is covered with a unique, rough texture that feels like sandpaper. This outer layer is an active biological system that plays a profound role in the animal’s survival and efficiency in the water.
The Technical Term for Shark Skin
The unique structures composing a shark’s outer layer are scientifically known as dermal denticles. This Latin term translates literally to “tiny skin teeth.” They are sometimes referred to as placoid scales, particularly in older biological texts. Unlike the flat, plate-like scales of other fish, these structures are small, tooth-like projections embedded in the skin. The denticles create the abrasive feel of the skin, which sailors historically used as a rough abrasive material.
Anatomy and Structure of Dermal Denticles
Each denticle is a complex, miniature structure. Its core contains a pulp cavity housing connective tissue, blood vessels, and nerves, similar to a tooth root. This internal structure is surrounded by dentine, a hard, calcified tissue providing structural support. The outermost layer is capped by an extremely hard, enamel-like substance called vitrodentine or enameloid.
These structures grow out of the shark’s dermis and are anchored in the skin. Unlike the scales of bony fish, denticles do not grow larger throughout the shark’s life. Instead, new denticles are added as the shark grows to cover the expanding surface area. Each denticle points backward toward the tail, which is consistent across the body. This arrangement means stroking a shark from head to tail feels smooth, but rubbing in the opposite direction feels coarse and abrasive.
How Shark Skin Reduces Drag
The function of dermal denticles is to manipulate the flow of water over the sharkâs body, increasing swimming efficiency. Microscopic ridges, called riblets, run along the crown of each denticle and are aligned in the direction of water flow. This riblet structure interacts with the boundary layer of water to reduce skin friction drag, a major force resisting movement through fluid.
The denticles prevent the formation of large, chaotic vortices in the water next to the skin. By keeping the water flow streamlined and organized, the denticles reduce the energy the shark must expend to move forward. This mechanism allows fast-swimming species, like the Shortfin Mako, to glide through the water with less resistance and reach higher speeds. A secondary advantage is that the textured surface creates a hostile environment for microorganisms, preventing biofouling (algae and barnacles from attaching).
Technology Inspired by Shark Skin
The design of dermal denticles has inspired biomimicry, a field of engineering that applies nature’s solutions to human problems. The drag-reducing principles were applied to competitive swimwear, most notably the Speedo Fastskin line. These suits featured fabric with a riblet pattern intended to mimic the shark skin’s ability to control water flow and reduce friction.
The denticle design has also been adapted for the transportation industry, particularly for surfaces moving through air and water. Riblet films are applied to the fuselages and wings of commercial aircraft to reduce aerodynamic drag, translating to fuel savings. Similarly, the patterns are incorporated into anti-fouling hull coatings for ships, providing a non-toxic way to prevent the buildup of marine organisms and maintain efficiency. The micro-groove texture is also used to create antibacterial surfaces in hospitals, where the pattern physically prevents bacteria from adhering.