Why do your fingers wrinkle in water?
The Real Answer
Your fingers wrinkle in water because the outer layer of skin (the stratum corneum) absorbs water and swells, but it's attached to the tissue underneath. Since the outer layer expands more than the inner layer can accommodate, it bunches up and creates wrinkles. This process is called maceration. Your fingertips are also covered in a natural oil that water strips away, which breaks the waterproof barrier and allows water to penetrate deeper into the skin.
Your fingers spend their entire lives staying dry and prepared for work, and then you put them in water for five minutes and they immediately surrender and give up. They literally wave the white flag. Your hands are like soldiers with the worst morale — one splash and they're like 'I'm out, I'm becoming a raisin.'
Why People Ask This
This is one of those things you notice in the bath or shower and suddenly can't stop noticing. The wrinkles happen so fast and so dramatically that people assume it's dehydration, but it's actually the opposite — it's your skin absorbing water and literally staging a protest against being submerged. Most people are shocked to learn it's not a universal response; people with certain nerve damage don't get wrinkly fingers in water, which is how scientists figured out the nervous system is actually involved.