Have you ever stayed in a pool or bathtub so long that your fingers got wrinkly? This is normal — and can even affect your toes. But why does it happen?

Even though you can't see it, your skin is covered with its own special oil called sebum (say: SEE-bum). Sebum is found on the outermost layer of skin. Sebum moistens, or lubricates (say: LOO-bruh-kates), and protects your skin. It also makes your skin a bit waterproof. That's why water runs off your skin when you wash your hands, instead of soaking it in like a sponge would.

But staying in water for a long time washes away the sebum. Then, the water can penetrate the outer layer of your skin. This causes your skin to become waterlogged. So how does this lead to wrinkles? No one is really sure.

Some people think it's because the skin expands to allow extra water inside. The expanded skin ends up looking really wrinkly. Other people think that it's because the skin is tied down to the tissue underneath in certain places. So when the skin is full of water, it swells up (gets puffy), but only in places where it is not tied down, which makes it look wrinkly.

What should you do if this happens to you? Nothing. It goes away quickly on its own. You'll have more sebum on your skin in no time.

Reviewed by: Steven Dowshen, MD
Date reviewed: May 2013