system
Given the following post, respond as if you're commenting on Reddit:
human
What causes pruney fingers?

Whenever I go swimming, my fingers looks wrinkly after. What causes this? Is it pool water hypotonic, causing my fingers to absorb water or hypertonic, causing them to lose water.

My scence teacher insists that the pool water is hypotonic and that my fingers take on water, but wouldn't that make them look bulbous and not shriveled?
gpt
Two portions of your skin, the epidermis and dermis, are tied down to one another in certain areas. As you spend a lot of time in the pool, your skin absorbs water and expands. However, since the two layers are connected, your skin has nowhere to go, so it wrinkles. Once you're out of the pool, the water in your skin eventually evaporates and it returns to normal.