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Now you're clean. The last step in the bathroom is getting dry. (And as grandma said, if you don't dry yourself, you might get a cold.) The question is: how is the hairdryer drying?

The hairdryer needs to force a lot of air around. It is an electrical device. A motor is sucking air in, heating it thanks to an electrical resistance (like that used in an electric oven) and forcing it outwherever you decide to aim it. This hot air meets the water on your hair, heats it and turns it into water vapor. Actually, no need of a hairdryer. Eventually your hair will dry by itself, but it's going to take sometime, a lot of time.

Hot air is better than cold air, because hot air is able to absorb more water vapor than cold air. F orcing the air into your hair is great because it improves convection. And convection is the key. Water on your hair is not thrown away, it is evapored.

And the hairdryer provides that last little moment of warmth before going back to the cold, cruel world outside the bathoom.