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Proponents of "no poo" claim that there is no medical reason for humans to wash their hair with synthetic shampoos, and that washing practices are determined by cultural norms and individual preferences, with some people washing daily, some fortnightly, and some not at all. From a clinical point of view, "the main purpose for a shampoo is to cleanse the scalp", though "most patients would disagree[,] stating that the purpose of shampoo is to beautify the hair".
The first synthetic shampoos were introduced in the 1930s, with daily shampooing becoming the norm in the US by the 1970s and 1980s. Proponents of "no poo" believe that shampoo removes the natural oils (sebum) produced by the scalp, causing the scalp to produce more oil to compensate. They also believe that regular shampooing causes a "vicious cycle" to develop as it becomes necessary to shampoo regularly to compensate for the excess oils produced by the scalp (which are produced in response to being stripped from the scalp by the previous shampooing). The time proponents believe it takes to break the cycle after adopting "no poo" practices varies, however a "two- to six-week period" is typical.
According to some dermatologists, a gradual reduction in shampoo use will cause the sebaceous glands to produce at a slower rate, resulting in less oil on the scalp and hair.
The purest form of "no poo" adoption is to use only water to wash hair, however there are other approaches possible by people wishing to avoid oil-stripping substances and chemicals that they consider unnecessary for the maintenance of their hair. Methods for washing hair without shampoo include washing with dissolved baking soda followed by an acidic rinse such as diluted vinegar. Also honey and various oils (such as coconut oil) can be used. Japanese traditional hair cleansing is with seaweed powder.
Following a 2007 radio interview that Australian Richard Glover held with Matthew Parris (a Times columnist "who hadn't shampooed for more than a decade"), Glover "decided to challenge his audience to go without shampoo for six weeks". Of the over 500 participants in the challenge, 86 percent reported that "their hair was either better or the same" following the challenge.
Proponents of "no poo" claim that there are several benefits to avoiding shampoo.
Chemical additives' effect on the body
One reason is concern about the effect of ingredients typically found in commercial hair care products. Shampoo typically contains chemical additives such as sodium lauryl sulfate and sodium laureth sulfate, which can irritate sensitive skin or if not thoroughly rinsed. Such chemical additives are also believed by some consumers to dry out their hair. The Environmental Working Group (EWG) compared the ingredients in 42,000 personal care products against 50 toxicity and regulatory databases and found that most shampoos have at least one chemical that "raises concern" (although the hair care industry counters by claiming that the chemicals are safe in the concentrations used). The group flagged the following groups of ingredients as hazardous: fragrances, due to containing unknown constituents, parabens, possibly linked to endocrine disruption and neurotoxicity, DMDM hydantoin, due to possible allergy concerns, and 1,4-dioxane, which the Environmental Protection Agency has labelled as a probable human carcinogen. Some disagree with the EWG’s assessments while others think they aren’t strong enough.
Some shampoos also include silicone derivatives (such as dimethicone), which is claimed to coat the hair. While it is claimed 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 proponents assert coats the hair is also claimed to prevent moisture from entering the hair, eventually drying it out.
In 2013, the FDA announced a review of triclosan, contained in antibacterial shampoos and soaps. Triclosan was found to affect hormone levels in animals. It has also been found to contribute to antibiotic resistance.
Shampoo and other beauty products are sources of pollution. The containers which hold them are often made of plastic, which contributes to plastics pollution.
Besides the containers, the products themselves contain chemical pollutants which are not always processed by waste treatment. One study shows that the fungicide present in anti-dandruff shampoos is present in environmental water at elevated concentrations, which can have negative effects on algae and plants.
Cost is also a reason some people decide to use "no poo" techniques instead of commercial hair care products.
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