General Knowledge
Why do your fingers wrinkle in the bath?
- Your nerves do it on purpose, for grip
- The skin soaks up water
- The skin dries out
The answer is Your nerves do it on purpose, for grip. It is an active nervous response - it improves grip on wet things.
Not because the skin soaks up water, which is the usual explanation and appears to be wrong. It is an active nervous response: blood vessels under the skin constrict, pulling the surface into ridges. The evidence is that fingers with nerve damage do not wrinkle at all, which a passive swelling could not explain.
That makes it a feature rather than a side effect, and the leading idea is grip - the ridges behave like tyre treads, channelling water out from under the fingertip. A 2013 study found people handled wet objects faster with wrinkled fingers and saw no difference with dry ones, which fits.
The result has not gone unchallenged; a later attempt to reproduce the grip advantage found none. So the mechanism is settled and the purpose is not. Surgeons have used the sign diagnostically for decades regardless - a hand held in water that fails to wrinkle points at a nerve problem, and it is one of the cheapest tests in medicine.