Skin friction ridges on a human fingertip

Scanning electron micrograph of the surface of a fingertip, 3x2mm in size. The picture shows friction ridges with sweat pores (yellow) along their top, separated by furrows. The ridges serve to enhance grip. Grip depends on the area of contact and the degree of moisture at the interface between the skin and a gripped object. The contact area is increased by sweat softening the ridges, causing them to flatten. Adhesion needs some moisture; sweat also provides this. Excess moisture (wet fingers or objects) lowers adhesion. The furrows then act as drains, and sweat secretion stops. Friction ridges are found only on human hands and feet and the paws of primates and koalas. They refine our sense of touch in ways we do not always realise. This is exploited by electronic devices to enhance engagement ( touchscreens, virtual reality or the "metaverse") by the process of haptic feedback., Photo by DR JEREMY BURGESS/SCIENCE PHOTO LIBRARY