WHY do our fingers do prune impressions when soaked? It could be an adaptation that gives us better grip underwater.
Fingers and toes wrinkle in water after about 5 minutes due to the constriction of blood vessels. This reduction in volume pulls the skin inward, but as the skin's surface area cannot change, it wrinkles. This mechanism is controlled by the autonomic nervous system. When nerves to the fingertips are severed, fingers no longer wrinkle underwater.
A study in 2011 showed that wrinkles form a pattern of channels that divert water away from the fingertip – akin to rain treads on tyres. The team thought that this could aid grip.
To find out, Tom Smulders and his team at Newcastle University, UK, timed people as they transferred wet or dry objects from one box to another with and without wrinkled fingers.
With wrinkles, wet objects were transferred about 12 per cent faster than with unwrinkled fingers. The time it took to transfer dry objects was the same regardless of wrinkles.
So why aren't our digits always prune-like? "With wrinkles, less of your skin surface touches the object, so there may be issues of sensitivity," Smulders suggests.