Why do wrinkles develop in our fingers when they are immersed in water for a long time?

Our skin has a protective top layer, called the stratum corneum. The primary function of this layer is to provide the much-needed protection to the underlying tissues from injury. With the primary reason being to provide protection, stratum corneum found in palms, fingers, soles and toes - areas that are more prone to mechanical abrasion - are much thicker compared with the layers found elsewhere. Stratum corneum, made of protein and fats, has a tendency to absorb water. And the absorption is seen to be maximum in these areas where the layer is the thickest. But with no room provided for the layer to expand on absorbing water, the most natural way to accommodate the expanded layer is to form wrinkles. It has been found that the time taken for wrinkles to form in these areas is influenced by the water composition.

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Seawater, which has a high mineral content, tends to keep water from penetrating into the skin. On the other hand, river water and water available in households have relatively lesser mineral content and this plays a direct role in the ability of the layer soaking in more water and forming more wrinkles and more quickly when immersed in water. This can be easily seen by immersing one's hand in household bathing water and noting the time taken to see wrinkles developing and the time taken for wrinkles to develop when swimming in sea water. Again, a distinction has to be made on the level of salinity of seawater. It would probably take a relatively longer time for wrinkles to develop when swimming in the Dead Sea compared with the Arabian Sea or Bay of Bengal. However, the wrinkles formed are transient by nature. The skin returns to its normal state once it loses the absorbed water. Hence it is different from wrinkles seen in aged people. In this case, wrinkles are formed not due to absorption of water but due to a predominant loss of elastic tissue in the underlying dermal layer of the skin, two layers beneath the outermost stratum corneum.

Source: thehindu.com