Some people use volumising shampoo, others slather on conditioner for a silky look.

Now, increasing numbers of people are opting to follow another haircare regime altogether – completely avoiding shampoo.

Advocates of the 'no poo' movement, as it is called, forgo conventional soapy detergents.

Instead, they wash their hair with only with water, or use natural ingredients such as vinegar, raw eggs, porridge and chalk on their locks.

Others, such as Kim Kardashian, Shailene Woodley, Adele, Gwyneth Paltrow and Jessica Simpson say they delay washing their hair for days, weeks and even months on end – but do use shampoo during their wash.