Listen Now Download as mp3 from the show Naked Science Q&A and the Edinburgh Science Festival
Linda, Norwich asked:
Why do I get really thirsty when I have a bath?
It could be that youíre having a very hot bath and when you have a very hot bath your body temperature goes up very high. Normally you would regulate body temperature by sweating. When you sweat water moves onto the surface of your skin. That water evaporating then carries heat away from the bodyís surface. Thatís called latent heat of evaporation and when water evaporates in this way it carries away extra heat from you and cools you down. If youíre in a steamy bathroom itís much harder for the water to evaporate and also if youíre submersed in the bath itís impossible for the water to evaporate from that surface so your temperature goes up. This means you can actually end up feeling as though youíve lost lots of water because youíre so warm and the bodyís reflex is to encourage you to drink.