What's the longest you can leave your hair without washing it for? A day? Three days? Perhaps a week? For some, that's nothing.
Over in the US, a group of girls are taking part in the 'no poo' movement. They've given up using shampoo at all. No hair washing, no dry shampoo, nothing. But why?
Huffington Post Style spoke to Jaquelyn Baers, a firm believer in the movement, to find out why it's catching on.
Baers told the site that she was concerned about using the chemicals found in shampoos. She decided to swap regular hair products for organic shampoos five years ago.
As these alternatives got expensive, Baers then tried making a natural alternative form baking soda and apple cider vinegar. "It was making my hair dry and greasy," she said in her interview. So after two years of experimenting, she said goodbye to shampooing completely.
And the results? After going through a difficult stretch of bad hair days, Baers perservered. Her hair started to look healthier and full of shine and she's stuck with using plain old water ever since.
Want to give the no shampoo thing a try? Find out more about the 'no poo' movement at Baers' blog LittleOwlCrunchyMomma.