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There is, in normal circumstances, no medical reason for humans to wash their hair, and 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" practices 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).
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. In the 2010 book Packing for Mars, Soviet research is quoted as "the skin halts its production of sebum—after five to seven days of not bathing...." The time taken to break the cycle after adopting "no poo"-practices varies, however a "two- to six-week period" is typical.
Chemical additives' effect on the body
People adopt "No poo" practices for many reasons, but 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 the skin of sensitive people (or of anyone if not thoroughly rinsed). Such chemical additives are also believed by some consumers to dry out their hair. The controversial Environmental Working Group, based in Washington, DC, 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 (the ingredients forming the fragrances are not disclosed), parabens (linked to endocrine disruption and neurotoxicity concerns), DMDM hydantoin (allergy concerns), 1,4-dioxane (which The Environmental Protection Agency has labelled as a probable human carcinogen).
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, especially in countries in the global south. 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.
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.
- Dahl, Melissa (April 23, 2009). "Ditching shampoo a dirty little beauty secret". MSNBC. Retrieved March 23, 2012.
- Aubrey, Allison (March 19, 2009). "When It Comes To Shampoo, Less Is More". NPR. Retrieved March 23, 2012.
- Jennifer Marsh, John Gray and Antonella Tosti, Healthy Hair (Springer, 2015), p. 117. DOI (for the relevant chapter): 10.1007/978-3-319-18386-2_7.
- Zoe Diana Draelos, 'Hair Cosmetics', in Hair Growth and Disorders, ed. by Ulrike Blume-Peytavi, Antonella Tosti and Ralph M. Trüeb (Springer, 2008), pp. 499-513 (p. 500). DOI: 10.1007/978-3-540-46911-7_25.
- "From Pert: Do You Wash and Go?". Company Science Behind the Brands. Procter and Gamble. Archived from the original on February 16, 2007. Retrieved March 24, 2012.
- Roach, Mary (2010). "Chapter 10: Houston, We Have a Fungus". Packing for Mars. New York: W. W. Norton & Company. pp. 191+. ISBN 9780393068474.
- Middlewood, Erin (April 12, 2009). "A clean break from shampoo". The Columbian. Vancouver, WA. Retrieved August 13, 2012 – via HighBeam. (subscription required (. ))
- Saint Louis, Catherine (September 29, 2010). "Sulfate-Free Products Have Some in a Lather". The New York Times. Retrieved March 23, 2012.
- "Triclosan:What the consumer should know". FDA.
- "Scientific American: dandruff shampoos mess up the water". Scientific American.
- Grossman, Anna Jane (February 21, 2008). "Of Course I Washed My Hair Last Year (I'm Almost Certain)". The New York Times. Retrieved March 23, 2012.