Why do you need a drink after swimming?
Question
When you go for a swim or have a bath, the first thing you want to do is go and have a drink. Why is that, when you've been sitting in water the whole time?
Julie, Holborn
Answer
Name: James O'Brien
Qualification: None in this field
Answer: Fanfare please... the answer is OSMOSIS! Please let it be osmosis!
** Definitive **
Name: Jo, Feltham
Qualification: Research scientist and developmental biologist
Answer: You're right about osmosis causing your fingers to go wrinkly in the bath. But it has nothing to do with why you are thirsty. For the wrinkles, you have more salt in your skin than in the bath, so the water goes into your skin and your skin swells. The reason you get wrinkles is that your hands and feet have patches of dead skin on them, which don't swell. The reason you get thirsty if you've been the shower is that normally when you get hot, you sweat to get rid of that heat. But when you're immersed in water, sweating doesn't work as there is no evaporation. So instead, your body causes you to be thirsty so that you have a glass of water and that will cool you down.