Why do fingers become wrinkled if they are soaked in water for too long?

In daily life

This phenomenon often occurs

After taking a bath or washing your hands for a long time, your skin will become wrinkled.

After wiping off the water, it will slowly return to its original smooth state.

What's going on

Many of you may say without thinking: Isn’t it just soaking in water? The skin cells absorb too much water and become swollen?

However, when soaking in the same water, why do only the pads of the fingers and toes become wrinkled, while the skin on the other knuckles and the back of the hands remain basically normal?

Today we will study:

Why do wrinkles occur when soaking in water for too long?

Why do only fingers and toes get wrinkled?

What is the significance of this wrinkling?

Causes of wrinkles

Simply put, skin wrinkles are caused by soaking in water for a long time, which causes the stratum corneum cells to absorb water and swell . Currently, there are two explanations in the medical community about the principle of stratum corneum cells absorbing water and swelling:

One is that the cell membrane has a semi-permeable membrane property, which allows water to flow from the low concentration side to the high concentration side. Another is that there are a lot of proteins in the corneocytes, which have a capillary effect on water, just like a sponge absorbs water.

1. Semipermeable membrane characteristics

Do you remember the "osmosis" we learned in textbooks? Under this physical action, water will flow from the side with lower concentration to the medium with higher concentration.

Our skin is generally divided into three layers, namely the epidermis, dermis, and subcutaneous tissue. The cells in the epidermis will constantly divide into new cells and renew the dead old cells.

After the old cells die, they become keratinocytes on the surface of the skin. The process of skin absorbing water and producing wrinkles mainly occurs in the keratinocytes .

Although the stratum corneum cells on the surface of the skin have become "dead cells" due to metabolism, they still have cell membranes and still have the function of "semi-permeable membranes" that allow material molecules to enter and exit cells .

At this time, due to the "osmotic effect", the concentration of substance molecules inside the cells is obviously higher than the concentration of water molecules outside. Water will flow from the aqueous solution into the stratum corneum cells of the skin, and the skin will absorb water.

The stratum corneum cells on the outer layer of the skin will become "chubby" after absorbing enough water. The inner layer of skin cells cannot absorb water due to the obstruction of the outer layer of cells, so their volume is much smaller than that of the outer layer of cells .

In this way, the outer layer of cells soaked in water will be much "fatter" than the inner layer of cells, and the surface area of ​​the outer layer of cells will also increase, while the inner layer of cells will not change much. The expanded area of ​​the outer layer of cells will bulge, thus forming uneven wrinkles.

2. Capillary action

Simply put, capillary action means that the force exerted by object 1 on the molecules of object 2 is greater than the force that holds object 2 together, so some molecules in object 2 will defect to object 1.

In the example of skin water absorption, the attraction of a large number of protein molecules inside the stratum corneum cells on the skin surface to water molecules is greater than the cohesive force between water molecules , thus producing capillary action and absorbing the water molecules into the cells.

In fact, there are many such examples in life. The water absorption of paper towels and sponges is caused by capillary action.

Why are fingers and toes more prone to wrinkling?

• Because the fingers and toes require more frequent work, the metabolism of the skin will be accelerated, the stratum corneum will be thicker, and the swelling effect will be more obvious .

• The sebaceous glands in the fingers and toes secrete less oil , which has a smaller barrier effect on moisture, making it easier for moisture to enter the surface cells.

• There is not much subcutaneous fat in areas such as fingers and toes, and fat has good elasticity, so areas with more subcutaneous fat are relatively less likely to wrinkle.

What do these wrinkles mean?

Quite a number of studies have shown that the wrinkling of fingertips after soaking in water is a behavior regulated by the sympathetic nervous system .

This phenomenon dates back to 80 years ago, when doctors discovered during World War II that soldiers with damaged extremity nerves would not wrinkle their fingers after soaking them in water. So far, many teams have also discovered this phenomenon in patients with nerve damage due to different reasons.

Nowadays, observing whether fingers wrinkle after soaking in water has even become a detection method to determine whether the sympathetic nerve function of the limbs is normal .

The current mainstream view is that when fingers are soaked in water for more than 5 minutes, the sympathetic nerves will regulate the contraction of blood vessels in the fingers, the volume of blood vessels in the finger tissue will decrease, leaving some space in the tissue, forming negative pressure, and other surrounding tissues will collapse to fill these spaces, forming wrinkles on the skin.

It is speculated that the significance of these wrinkles to humans may be mainly that they can increase the friction of the fingertips , making it easier for humans to move and work in humid environments for a long time, thereby improving productivity. It can be said that this is a natural evolutionary ability of humans.

Mark Changizi, an evolutionary neurobiologist at 2AI Labs in Boise, Idaho, and his colleagues believe that there must be an evolutionary mechanism for the wrinkling of fingers. The team found that the pattern of wrinkles on the fingers is very conducive to water drainage, and this drainage network can increase the friction when grasping objects .

During the study, participants tested the grip of marbles of different sizes using dry fingers and fingers soaked in warm water for 30 minutes. Some of the marbles were dry and some were wet. The results showed that the soaked fingers were faster at grasping the wet marbles , but there was no significant difference between the two for the dry marbles.

"We've shown that wrinkled fingers have a stronger grip in wet conditions, similar to how the tread on a car tyre increases its grip by increasing the area in contact with the ground," said co-author Tom Smulders, an evolutionary biologist at Newcastle University in the UK.

Smulders added that wrinkled fingers would have helped our ancestors gather food from wet vegetation or rivers, while wrinkled toes would have helped them stand more steadily in the rain.