Usually the skin on your hands is tight. Soaking in water for a long time, the skin will absorb a lot of water and become slack, thus forming wrinkles. You may ask why there are no wrinkles in other parts of the body. The reason is that there is more subcutaneous fat in other parts of your body. Even if the skin has wrinkles, the elasticity of fat will spread them out, and there is less subcutaneous fat on your hands, so wrinkles will remain!

This has nothing to do with the water absorption of cells. Cells have a self-regulating mechanism and will not allow themselves to inhale excessive water, otherwise they will burst!

There are two theories about this problem. ...

Because water can relax and soften tissues.

Our skin is actually covered with a thin layer of oil, in order to prevent the skin from absorbing water directly from the outside. But when we soak in warm water or hot water for about half an hour, this layer of oil will be removed by warm water, so the skin begins to absorb water. The surface layer of our skin is a layer of "epidermis", and under the epidermis is "dermis"; Epidermis and dermis are not completely tightly "bonded" together. Epidermis is tightly "tied" to dermis by connective tissue in some areas, but not in some places. Therefore, when the epidermis "swells" after absorbing water, the "tied" place is imprisoned and depressed; From the outside, the skin surface is uneven, like wrinkles. However, because the palms and toes of hands and feet are the thickest parts of the whole body epidermis, wrinkles are obvious; Other parts of the skin should also have this effect, but it is not easy to be detected. Soaking in water for too long, the epidermis absorbs water and expands, so it becomes wrinkled. In the past, some women specialized in washing clothes for others, and their hands were soaked in water for a long time, and their fingers were often wrinkled, which became a professional "disease" (it should be said that it is a feature). In ancient times, the washerwoman was called "floating mother", so this finger phenomenon was also called "floating mother skin".

In other words:

Because the concentration of liquid in the body is higher than that of fresh water, if the finger is soaked in fresh water for a period of time, the water will flow into the epidermal cells of the skin, and the cells will expand and deform.

On the contrary, because the concentration of liquid in the body is lower than that in seawater, when we swim in seawater, water will flow out of the body from epidermal cells, and the cells will shrink and deform accordingly.

In addition, there are bundles of elastin at the bottom of the skin, which closely adhere to epidermal cells, causing uneven contraction or expansion of finger skin, resulting in skin wrinkles.