The raisin finger story.

It was a cold winter morning. Tony was reluctant to take a bath. His mom prepared a warm bubble bath with his favorite floating toys. Tony was excited and soaked himself in for an hour. But to his horror, when he came out, instead of smooth and supple, his fingers were all wrinkled. Tony felt as if his fingers had transformed into raisins. He was annoyed and asked his mom, why did the water do this to him?

Let us help Tony's mom explain to him the reason behind the raisin fingers.

The wrinkles that occur in skin after prolonged exposure to water are sometimes referred to as pruney fingers or water aging. This is a temporary skin condition where the skin on the palms of the hand or feet becomes puckered.

Let us explore the science behind it and the different hypothesis that revolve around this.

Osmosis concept - For years it was thought that the dry skin absorbs water by osmosis and swells up. The stretched skin appears to be wrinkled, as it has to accommodate in the same area. But research proved that it is not due to the osmosis.

Keratin thesis – The keratin-laden skin when immersed in water, causes the skin to expand, resulting in a larger surface area, forcing it to wrinkle. Usually the tips of the fingers and toes are the first to wrinkle because of a thicker layer of keratin and an absence of hairs that secrete the protective oil called sebum.

The nervous system theory – This is the most widely accepted theory for the pruney finger phenomenon. In 1935, the studies on nervous disorder by Lewis and Pickering showed that skin wrinkling, did not occur in the areas of the patients' skin normally innervated by the damaged nerve. This clearly suggested the important role of our nervous system in wrinkling. 

Water probably initiates the wrinkling process by altering the balance of electrolytes in the skin as it diffuses into the hands and soles through the numerous sweat ducts in them. Nerves fire as the electrolytes alter the stability of the synaptic membrane .The Sympathetic nervous system is activated, which also governs breathing and heart rate. Rather than swelling up, fingertips shrink when they wrinkle because the blood vessels inside them contract. The blood vessels of the fingers constrict, the decreased volumes in the deep layers of soft tissue essentially pull the skin, creating the folds that we know as wrinkles.

The purpose of wrinkling- Wrinkling response may have an evolutionary benefit.  It could have helped our ancestors with gathering food from wet vegetation or streams or being able to get a better footing in the rain. According to an experiment done by Tom Smulders, an evolutionary biologist at Newcastle University, UK – “We have shown that wrinkled fingers give a better grip in wet conditions — it could be working like treads on your car tyres, which allow more of the tyre to be in contact with the road and gives you a better grip". Wrinkled fingers apparently made no difference when it came to picking up dry objects. Our fingers do not wrinkle all the time as there is one Achilles’ heel to this great power of grip - wrinkled fingers tend to be more sensitive and can increase the risk of damage through catching on objects. So, the wrinkles are actually your friend in need.

Unique pattern- Mark Changizi an evolutionary neurobiologist at Idaho, proposes that the wrinkles in fingers work like rain treads on tires. They create channels that allow water to drain away as you press your fingertips on to wet surfaces, which would allow your fingers to make better contact giving you a better grip.

After the explanation Tony’s mom was satisfied and this left Tony feel proud that he too had the evolutionary benefit.

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