The case put forward by the No Poo movement! –
No poo (no shampoo) is a collective term for methods of washing hair without commercial shampoo. (Some people may make their own shampoo.)
Shampoo typically contains sulfates such as Sodium Lauryl Sulphate and Sodium Laureth Sulphate, which some believe to be drying for the hair. Some shampoos also include silicone derivatives such as Dimethicone, which coats the hair. While some find that silicone derivatives protect the hair and make it more manageable (Dimethicone is a common ingredient in smoothing serums and detangling conditioners), the film that coats the hair can also prevent moisture from entering the hair, eventually drying it out. Some shampoos include mineral oils which, while they provide softness and sheen, are bad for the hair because they are not water soluble and hence require a shampoo with sodium lauryl sulfate (SLS) which is drying for the hair. Some shampoo may include alcohol which, while it may clean the hair, is bad because it dries the hair.
Shampoo contains anionic and amphoteric surfactants, substances which are good at dissolving fats but also dry the hair and the scalp, which results in dry and lifeless hair. Shampoo is alkaline and opens the hair cuticle, which takes a toll on the hair. Hair should be rinsed with cold water to close the hair cuticle.
Methods for washing hair without shampoo include washing with dissolved sodium bicarbonate, followed by an acidic rinse such as diluted apple cider vinegar. Also honey and various oils (such as coconut oil) may be used.