As the warmer months quickly approach, summer getaways are likely on many travelers’ minds. Whether they’re conjuring up images of pristine beaches or poolside cocktails or vertigo-inducing waterslides, getting wet is synonymous with summer travel.
And for those who love cooling down by jumping in a pool, there’s probably one mystery about the whole experience left unsolved: Why do fingers and toes get wrinkly after spending time in the pool, but no other part of your body does?
The answer, as always, lies in science.
Fingers, toes and the soles of feet are all covered in something called “glabrous skin,” which basically just means skin where hair won’t grow.
Many people assume that when skin here wrinkles, it’s just water passing into the skin’s outer layer and making it swell up. However, in the 1930s, scientists proved that this human reaction does not happen in people with certain types of nerve damage. Therefore, skin wrinkles are involuntarily controlled by the body’s nervous system. It’s actually the blood vessels below the skin constricting.
There are a few other theories suggesting why skin wrinkles: Some biologists believe that the wrinkling is caused by dead keratin cells absorbing water. Because skin on the hands and feet has the highest counts of dead keratin cells, that could be why they are the only parts of the body to wrinkle.
Whatever the cause, the reaction is most likely something left over from evolution. When skin gets wrinkly, it makes it easier to grab things. Our ancestors may have used this trait to gather food from wet vegetation or make it easier to walk in the rain.
Today, the most we probably use it for is trapping small items that fall off the edge and sink to the bottom of the pool.
This article originally appeared on TravelandLeisure.com