When fingers and toes are immersed in water, the outermost layer of the skin swells as it absorbs water. This layer is tightly attached to the skin underneath, so it compensates for the increased area by wrinkling. The wrinkling is caused by blood vessels constricting below the skin, which is an active, adaptive process controlled by the sympathetic nervous system. Wrinkly fingers and toes give a better grip in wet conditions, working to channel away the water like treads on car tires. Theories suggest that the role of digital vasoconstriction (narrowing of blood vessels) of water immersion wrinkling of the skin is responsible for the wrinkling. When hands are immersed in water, the nerve fibers are triggered to “shrink,” and glomus bodies (body temperature regulators in the skin) in the hand lose volume, which then pulls the skin structures downwards to produce wrinkling. Studies on patients with loss of nerve function in their hands due to a disorder or replantation of amputated fingers exhibit no or slight wrinkling in the fingers when immersed in water. As the nerve functions return, so does the wrinkling.
In summary, hands wrinkle in water due to the outermost layer of the skin swelling as it absorbs water, and the blood vessels constricting below the skin. This wrinkling is an active, adaptive process controlled by the sympathetic nervous system and gives a better grip in wet conditions.
