Wilder-Smith and his colleagues proposed that when our hands are immersed in water, the sweat ducts in our fingers open up to allow water in, which leads to an imbalance in the salts in our skin. This change in the salt balance triggers the firing of nerve fibres in the fingers, leading to the blood vessels around the sweat ducts to constrict. This in turn causes a loss of volume in the fleshy area of the fingertip, which pulls the overlying skin downwards so that it distorts into wrinkles. The pattern of the wrinkles depends on the way the outermost layer of skin – the epidermis – is anchored to the layers beneath it.