Actually, your fingers and toes aren’t wrinkling at all but puckering from swelling.
The thick outside layer of skin, called the stratum corneum, takes on excess water when saturatedsort of like when dried beans are soaked in water.
The underlying skin and connective tissue around the stratum corneum doesn’t absorb water and therefore doesn’t swell along with it. This anchoring of the skin tissue layers makes the swollen area appear puckered.
It’s not just the fingers and toes that do this, though they are easier to see because the stratum corneum is thickest in those areas.
When you see your fingers and toes wrinkling, take it as a sign that your entire body is on guard, preventing water, soap, dirt, and germs from invading through the skin.