First of all, this is certainly a normal phenomenon. Water can relax and soften tissues. Studies have shown that people's palms and soles of feet have the thickest skin, protecting hands and feet, which is why wrinkles are most likely to occur. Our skin is actually covered with a thin layer of grease, in order to prevent the skin from absorbing water directly from the outside. But when we soak in warm or hot water for about half an hour, the oil will be removed by warm water, so the skin begins to absorb water. The surface of our skin is an "epidermal layer", while the lower part of the epidermis is the "dermis". The epidermis and dermis are not completely "glued" together. In some areas, the epidermis is is tightly "bound" to the dermis by connective tissue, while in some places it is not. Therefore, when the epidermis "swells" by absorbing water, the "binding" place is limited and concave; From the appearance, the surface of the skin is concave and protruding, like wrinkles. The epidermis consists of tough dead cells. Under the microscope, these cells look like paving stones.
Generally speaking, the epidermis is is very thin, only about 0.01 mm, but the thickness of the epidermis of the palm and sole of the foot is up to or more than 0.5 mm, so the wrinkles are particularly obvious. In theory, swimming or bathing can also cause skin wrinkles in the chest and abdomen, but because there is almost no expandable cuticle in these areas, only a few tiny wrinkles appear. Once upon a time, some women specialized in washing clothes for others. Their hands were soaked in water for a long time, and their fingers were often wrinkled, which became a kind of occupational "disease" (should be said to be a feature). In ancient times, washwomen were called "floating mothers", so this kind of finger phenomenon was also called "floating mother skin".