Normally, most skin is covered by a thin, waterproof film of oily sebum. This substance, secreted by the sebaceous glands, keeps the skin supple and at the same time prevents moisture loss and also prevents water penetration.
However, when skin is in contact with water for relatively long periods of time in the bath or at the swimming pool for example – this film of sebum dissolves. The process is accelerated by the use of soap or other skin cleansers.
Outer layer consists only of dead, hard skin cells filled with the protein keratin. There is a layer of subcutaneous tissue beneath made up of living cells. This layer is water tight, this means water can’t seep past this layer.
Once the film of sebum has dissolved, water can penetrate the gaps in the outer layer of the skin.As a result, the skin expands and swells up. However, because the outer layer is firmly attached to the water-tight subcutaneous layer beneath, which is made up of living cells, creases form and the skin wrinkles.
A lot of hard skin builds up, especially on the fingers, toes and heels, where everyday activities place additional demands on the skin. The layer of hard skin on these parts of the body can be between five and 20 times thicker than on other parts. This is why these are the areas most prone to water penetration and where the skin wrinkles most noticeably moreover they have less sebaceous glands.
Some claim that wrinkling confers additional advantage of gripping object when the hands are wet. Clearly there is no disadvantage of wrinkled palm in water over a soft one!
Simple! when we get out of the bath or pool, the absorbed water quickly evaporates, the skin becomes smooth again, a new layer of sebum is produced by the underlying sebaceous glands. However this process is slow on soles and palms as these places have relatively less number of sebaceous glands.