Most people have experienced wrinkly finger syndrome - when fingertips turn paler and wrinkle after prolonged exposure to water.
There are two theories on how the wrinkles develop - the ‘shink’ model and the ‘swell’ model. Neither theory alone provides a full explanation. A 2017 study in the Annals of biomedical engineering provide fresh insight. The research team’s computational models suggest that both the ‘shink’ model and the ‘swell’ model are probably operating at the same time.
“Everyone has experienced wrinkly ﬁngers after an extended exposure to water. These wrinkles have been proposed as an evolutionary mechanism for a better grip of wet objects. However, besides experimental observations or mathematical theories, there is still not a clear agreement whether this is a result of the contraction of the hypodermis ( the ‘shrink’ model), the eﬀect of epidermal swelling (the ‘swell’ model), or the coupling of both mechanisms.”
But more research is still needed to fully explain the phenomenon.
“Without doubt, further experiments will help to close the debate about the origin of ﬁngertip wrinkling.”
See : Mechanics reveals the biological trigger in wrinkly fingers , P Sáez, AM Zöllner - Annals of biomedical engineering, 2017.