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Shampoo, when lathered with water, is a surfactant, which, while cleaning the hair and scalp, can remove the natural oils (sebum) which lubricate the hair shaft.
Shampooing is frequently followed by conditioners which increase the ease of combing and styling.
Additional recommended knowledge
The word shampoo in English usage dates back to 1762, with the meaning "to massage". The word was a loan from Anglo-Indian shampoo, in turn from Hindi chāmpo (चाँपो /tʃãːpoː/), imperative of chāmpnā (चाँपना /tʃãːpnaː/), "to smear, knead the muscles, massage". It itself comes from Sanskrit/Hindi word "champā" (चम्पा /tʃəmpaː/), the flowers of the plant Michelia champaca which have traditionally been used to make fragrant hair-oil.
The term and service was introduced by a Bengali entrepreneur Sake Dean Mahomed, who opened a shampooing bath known as 'Mahomed's Indian Vapour Baths' in Brighton, England in 1759. His baths were like Turkish baths where clients received an Indian treatment of champi (shampooing) or therapeutic massage. His service was appreciated; he received the high accolade of being appointed ‘Shampooing Surgeon’ to both George IV and William IV.
During the early stages of shampoo, English hair stylists boiled shaved soap in water and added herbs to give the hair shine and fragrance. Kasey Hebert was the first known maker of shampoo, and the origin is currently attributed to him.
Originally, soap and shampoo were very similar products; both containing surfactants, a type of detergent. Modern shampoo as it is known today was first introduced in the 1930s with Drene, the first synthetic (non-soap) shampoo.
From ancient times to this day, Indians have been using different formulations of shampoos using herbs like neem, shikakai or soapnut, henna, bael, brahmi, fenugreek, buttermilk, amla, aloe, and almond in combination with some aromatic components like sandalwood, jasmine, turmeric, rose, and musk.
How shampoo works
Shampoo cleans by stripping sebum from the hair. Sebum is an oil secreted by hair follicles that is readily absorbed by the strands of hair, and forms a protective layer. Sebum protects the protein structure of hair from damage, but this protection comes at a cost. It tends to collect dirt, styling products and scalp flakes. Surfactants strip the sebum from the hair shafts and thereby remove the dirt attached to it.
While both soaps and shampoos contain surfactants, soap bonds to oils with such affinity that it removes too much if used on hair. Shampoo uses a different class of surfactants balanced to avoid removing too much oil from the hair.
The chemical mechanisms that underlie hair cleansing are similar to that of traditional soap. Undamaged hair has a hydrophobic surface to which skin lipids such as sebum stick, but water is initially repelled. The lipids do not come off easily when the hair is rinsed with plain water. The anionic surfactants substantially reduce the interfacial surface tension and allow for the removal of the sebum from the hair shaft. The non-polar oily materials on the hair shaft are solubilised into the surfactant micelle structures of the shampoo and are removed during rinsing. There is also considerable removal through a surfactant and oil "roll up" effect. The foamy effect achieved by massaging shampoo into the hair is purely aesthetic.
Shampoo formulations seek to maximize the following qualities:
Many shampoos are pearlescent. This effect is achieved by addition of tiny flakes of suitable materials, eg. glycol distearate, chemically derived from stearic acid, which may have either animal or vegetable origins. Glycol distearate is a wax.
In the USA, the Food and Drug Administration (FDA) mandates that shampoo containers accurately list ingredients. The government further regulates what shampoo manufacturers can and cannot claim as any associated benefit. Shampoo producers often use these regulations to challenge marketing claims made by competitors, helping to enforce these regulations. While the claims may be substantiated however, the testing methods and details of such claims are not as straightforward. For example, many products are purported to protect hair from damage due to ultraviolet radiation. While the ingredient responsible for this protection does block UV, it is not present in a high enough concentration to be effective. Shampoos made for treating medical conditions such as dandruff are regulated as OTC drugs.
Vitamins and Amino Acids
The effectiveness of vitamins, amino acids and "pro-vitamins" to shampoo is also largely debatable. Vitamins and amino acids are the building blocks of proteins and enzymes within the body. While vitamins may be able to penetrate cells through the skin, amino acids and proteins are too large to enter a cell outside the bloodstream, and they can have no effect on dead tissue. Proteins are constructed from amino acids following an RNA blueprint inside the cell. A strand of hair is a long protein chain continually being added to at the root. The only way for an amino acid to be of any use is to be intentionally bound to other amino acids in a specific fashion by a living cell. Hair is not alive, and there is no possibility for an amino acid or protein to have any permanent effect on the health of the strand.
The case for vitamins is not as well understood. Some have demonstrated a moderate effectiveness in improving the health of skin, but most likely the benefit is derived from the effect of vitamins on living cells below the epidermis. Extending this benefit to hair, the vitamins and minerals could improve the health of new hair growth, but the benefit to existing hair is unsubstantiated. However, the physical properties of some vitamins (like vitamin E oil or panthenol) would have a temporary cosmetic effect on the hair shaft while not having any bioactivity.
Cosmetic companies have developed shampoos specifically for those who have dandruff. These contain fungicides such as zinc pyrithione and selenium sulfide which reduce loose dander by killing Malassezia furfur. Coal tar and salicylate derivatives are often used as well.
Some companies use "all-natural", "organic", "botanical", or "plant-derived" ingredients (such as plant extracts or oils), combining these additions with one or more typical surfactants. The effectiveness of these organic ingredients is disputed.
Alternative shampoos, sometimes labeled SLS-free, have fewer harsh chemicals - typically none from the sulfate family. They are claimed to be gentler on human hair.
Shampoo for infants and young children is formulated so that it is less irritating and usually less prone to produce a stinging or burning sensation if it were to get into the eyes. This is accomplished by one or more of the following formulation strategies:
1. dilution, in case product comes in contact with eyes after running off the top of the head with minimal further dilution;
2. adjusting pH to that of non-stress tears, approximately 7, which may be a higher pH than that of shampoos which are pH adjusted for skin or hair effects, and lower than that of shampoo made of soap;
3. use of surfactants which, alone or in combination, are less irritating than those used in other shampoos;
4. use of nonionic surfactants of the form of polyethoxylated synthetic glycolipids and/or polyethoxylated synthetic monoglycerides, which surfactants counteract the eye sting of other surfactants without producing the anesthetizing effect of alkyl polyethoxylates or alkylphenol polyethoxylates.
The distinction in 4 above does not completely surmount controversy over the use of shampoo ingredients to mitigate eye sting produced by other ingredients, or of use of the products so formulated.
The considerations in 3 and 4 frequently result in a much greater multiplicity of surfactants being used in individual baby shampoos than in other shampoos, and the detergency and/or foaming of such products may be compromised thereby. The monoanionic sulfonated surfactants and viscosity-increasing or foam stabilizing alkanolamides seen so frequently in other shampoos are much less common in the better baby shampoos. 
Shampoo for animals (such as for dogs or cats) should be formulated especially for them, as their skin has fewer cell layers than human skin. Cats' skin is 2-3 cell layers thick, while dogs' skin is 3-5 layers. Human skin, by contrast, is 10-15 cell layers thick. This is a clear example of why one should never use even something as mild as baby shampoo on a cat, dog, or other pet.
Shampoo intended for animals may contain insecticides or other medications for treatment of skin conditions or parasite infestations such as fleas or mange. These must never be used on humans! It is equally important to note that while some human shampoos may be harmless when used on animals, any haircare products that contain active ingredients/drugs (such as zinc in antidandruff shampoos) are potentially toxic when ingested by animals. Special care must be taken not to use those products on pets. Cats are at particular risk due to their instinctive method of grooming their fur with their tongues.
Solid shampoos or shampoo bars use as their surfactants soaps and/or other surfactants conveniently formulated as solids. They have the advantage of being spill-proof, and the disadvantage of being slowly applied, needing to be dissolved in use.
Stiff, non-pourable clear gels to be squeezed from a tube were once popular forms of shampoo, and can be made by an increase of the method used to increase viscosity of liquid products. Their containers could not be spilled, but unlike solids, they could still be lost down the drain by sliding off wet skin or hair. Formerly soap jelly was made at home by dissolving sodium soap in hot water ahead of the time it would be used for shampooing or other purposes, to avoid problem of slow application of solids noted above.
Shampoos in the form of pastes or creams were formerly marketed in jars or tubes. The contents were wet but not completely dissolved. They would apply faster than solids and dissolve quickly. Jar contents were prone to contamination by users and hence had to be very well preserved.
Early shampoos used in Indonesia were made from the husk and straw (merang) of rice. The husks and straws were burned into ash, and the ashes (which have alkaline properties) are mixed with water to form lather. The ashes and lather were scrubbed into the hair and rinsed out, leaving the hair clean, but very dry. Afterwards, coconut oil was applied to the hair in order to moisturize it.
Notes and references
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Shampoo". A list of authors is available in Wikipedia.|