More than you ever needed to know about shampoo and Hair!

I just finished my bio/organic chemistry class this semester.  One of our assignments was to find chemistry in life and write about it.  I didn’t intend to write 13 pages on shampoo, but once I started, it went deep!  This is probably way more than anyone needs to know about hair and shampoo, but I found it interesting.  Happy reading!

SHAMPOO and HAIR

Time to get ready for the day.  Opening the shower door, I look at the five to six bottles of shampoo and conditioner in there.  Why so many?  I like shampoo.  I love the feel of soft, clean hair.  However, shampoo bottles can be so confusing.  What are all the ingredients and why are they there?

We should start with hair itself.  It is so much more complicated than it seems.  There is hair all over your body.  Hair is associated with gender and race.  Hair is associated with personality.  Hair is the only body structure that is completely renewable without scarring.  Hair starts early in development.  A developing fetus has all of its hair follicles formed by 22 weeks’ gestation.  At this time there are 5 million follicles on the body. One million of those are on the head, and 100,000 are on the scalp. This is the largest number of follicles we will ever have – follicles are never added during life. As the size of the body increases as we grow older, the density of the hair follicles on the skin decreases.[1]

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What exactly is hair?  Hair has two parts, the follicle that is embedded in the skin and the shaft, the part we see.  At the base of the follicle is the papilla, which contains capillaries.  It is the living part of the hair.  The cells in hair divide every 23 to 72 hours, faster than any other cell in the body.[3]  The follicle is surrounded by two sheaths that protect and mold the hair.   The inner sheath surrounds the sebaceous gland, which produces sebum.

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The shaft of the hair is made of dead, hard protein called keratin.  There are three layers to the shaft – the inner medulla, then the cortex, with the cuticle on the outside.  The cuticle is formed by tightly packed scales in an overlapping structure similar to roof shingles.[5]

Hair is composed of approximately 50% carbon, 20% ox, 17% nitrogen, 6% hydrogen, and 5% sulfur.  Darker hair has higher levels of carbon than blonde hair.[6]  Hair initially starts out while.  Natural hair color comes from melanin, a pigment.  Hair color is dependent on the distribution of melanin in the hair cortex.[7]  Grey hair is the result of a decrease in pigment.  Why does this happen?  There are a few theories, whether it is a failure of the melanocytes (the cells that produce melanin), genetic factors, hormones, toxins,[8] or a buildup of hydrogen peroxide in the hair shaft.[9]

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Hair is a biological polymer.  Over 90% of its dry weight is made from proteins called keratins.  These proteins are held together with disulfide bonds, from the amino acid cysteine.[11]  The disulfide bond is a covalent bond.  It is a very strong bond. The shape of the bond determines the shape of your hair, be it straight or curly. Interestingly, hair straightening agents, and permanent waves are successful by manipulating the disulfide bonds, breaking them, allowing them to be reshaped, and then held in new form with a neutralizer.[12]

Sebum is a greasy substance.  This coats and protects the hair, along with the hair follicle.  Additionally, a healthy shine comes from sebum coating the outer keratin layer of each strand.  Too much of it, however, makes your hair look greasy.  Sebum is hydrophobic (water-hating); it cannot be rinsed away with water.[13]    Things like dirt, skin flakes, and smoke are attracted to sebum.  Additionally, sebum, because of its fatty acids, can oxidize, leading to that “you need to wash your hair” smell.

The English word shampoo originated in India about 300 years ago and, at first, entailed a head massage with some fragrant oil. The practice likely dates back centuries before that. Shampooing in the modern sense, though, with water to produce a soapy lather, is only about 100 years old.[14]

Before the advent of shampoos, people typically used soap for personal care. However, soap could be irritating to the eyes and incompatible with hard water, which left a dull-looking film on the hair.

In May 1908, there was an article in the New York Times with instructions on how to shampoo the hair, aimed specifically at women.  The article explains that hair is “best shampooed at night, following a thorough combing and brushing of the hair, and then carefully singeing all split ends. After an olive oil-based Castile soap is applied with a stiff brush, the hair is rinsed four times, the latter rinses with cooler water to prevent the head from overheating and limit the potential for catching a cold.”[15] This was a very rigorous regimen to follow.  However, in 1908, “hair specialists recommend the shampooing of the hair as often as every two weeks, but from a month to six weeks should be a better interval if the hair is in fairly good condition.”[16]

In the early 1930s, the first synthetic detergent shampoo was introduced, with the use of fatty alcohols.  These first fatty alcohols were derived from the body of sperm or bottle nose whales.[17] The 1960s brought the detergent technology we use today.[18]

Shampoo contains detergent, which act as an emulsifier to clean the hydrophobic sebum from your hair.  Molecules that readily mix with water are hydrophilic. Molecules that readily mix with oil are hydrophobic. Since we know that water and oil do not mix, then it follows that hydrophilic and hydrophobic compounds do not mix.

Image[19]  Part of the detergent molecule (“tail”) is hydrophobic (oil-attracting).  This binds with the sebum that is coating the hair.  The other end of the detergent molecule (“tail”) is hydrophilic (water-attracting), so that rinsing your hair will carry the detergent and sebum with it.[20]  Detergents in shampoo also act as surfactants.  The word surfactant is a combination of three words surface+active+agent.  Surfactants act as wetting agents to lower the surface tension of liquids, increasing contact between water and the hair (sebum and dirt mix).

When greasy dirt is mixed with detergent, the molecules arrange themselves into clusters that are called micelles.  The hydrophilic parts of the molecules point outward, adhering to the water.  This forms the outer surface of the micelle.  The hydrophobic parts of the molecules stick to the sebum and dirt, trapping it safely in the center of the micelle.  Because the oil is trapped on the inside of the micelle, the micelle itself is now water soluble and is rinsed away, taking the greasy dirt with it.

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(image from http://en.wikipedia.org/wiki/Micelle)

The more oil and grease there is to bond to, the less the shampoo will lather. This is why a second shampooing always lathers more (and probably why shampoo bottles tell you to “repeat”).[21] When greasy dirt is mixed with detergent, the molecules arrange themselves into clusters that are called micelles.  The hydrophilic parts of the molecules point outward, adhering to the water.  This forms the outer surface of the micelle.  The hydrophobic parts of the molecules stick to the sebum and dirt, trapping it safely in the center of the micelle.  Because the oil is trapped on the inside of the micelle, the micelle itself is now water soluble and is rinsed away, taking the greasy dirt with it.

Shampoo also generally contain a pH adjuster. Shampoo tends to be acidic (low pH).  If the pH gets too alkaline (high pH), the sulfur bridges in hair can break, damaging it.[22]   In hair that is healthy, the cells in a cuticle overlap like roof shingles.  In hair that is damaged, the cells are more open and ragged[23].  As hairs rub against each other, electrons transfer and can produce a static electrical charge, resulting in flyaway hair.  Shampoo should smooth the cuticle and cover it.  This smoothing action is achieved by controlling pH balance.  Proper pH balance of shampoo is maintained by the addition of buffering agents, such as citric acid.[24]

 

There are so many shampoos out there, ranging from relatively inexpensive to rather high-end.  Do we need to worry about what’s in our shampoo?  “Most of the chemicals that make up the ingredients in shampoos and other personal care products have never been tested or adequately assessed for safety by either the federal government or the manufacturers… Companies are free to use almost any ingredient they choose in personal care products, with no proof of safety required.” [25] “Cancer-causing chemical found in nearly 100 common soaps and shampoos.”[26] “Toxic Ingredients in Personal Care Products.”[27]  Are these headlines true?  How could this be?  I needed to find out more.

The ingredients on one of my current shampoo bottles is as listed:

Water (Aqua), Sodium Laureth Sulfate, Cocamidopropyl Betaine, Sodium Chloride, Fragrance (Parfum), Polyquaternium-10, Coceth-7, PPG-1-PEG-9 Lauryl Glycol Ether, Propylene Glycol, PEG-40 Hydrogenated Castor Oil, Citric Acid, DMDM Hydantoin, Tetrasodium EDTA, Hydrogenated Coconut Oil, Prunus Amygdalus Dulcis (Sweet Almond) Oil, Macadamia Ternifolia Seed Oil, PPG-9, Methylchloroisothiazolinone, Methylisothiazolinone, Yellow 5 (CI 19140), Red 33 (CI 17200), Blue 1 (CI 42090)[28]

Sodium Laureth Sulfate:  This is used in shampoo, toothpaste, and mouth rinse as foaming and cleansing agents. It is an alkyl ether sulfate.  Alkyl ether sulfates result from the sulfation of an ethoxylated fatty alcohol. Ethoxylation is the process by which ethylene oxide is added to a fatty acid alcohol to create detergent properties in a surfactant.[29]  Sodium laureth sulfate (SLES) has a rather bad rap.  A quick internet search brings up a     lot of warnings about the toxicity and carcinogenicity of this   ingredient.  This compound may contain the carcinogen dioxane.  The dioxane is a byproduct or processing SLES with other chemicals in order to reduce its harshness.  The Cosmetic, Toiletry and Fragrance Association discourage SLES for prolonged use, unless in extremely low concentrations. According to a U.S. Environmental Protection Agency study, sodium laureth sulfate applied above a 5 percent concentration produced severe irritation, hair loss and death in laboratory animals.[30] Sodium Laureth Sulfate:  This is used in shampoo, toothpaste, and mouth rinse as foaming and cleansing agents. It is an alkyl ether sulfate.  Alkyl ether sulfates result from the sulfation of

While SLS is an irritant, shampoo containing it is tolerable because it only comes into contact with the scalp briefly and is diluted with water while in use.[31]  In shampoo, it is used as a surfactant.

There are so many sulfate-free shampoos out there and most of them are pricy.  SLS can irritate skin in some people.[32]  So, for some people, it might make sense to go sulfate-free, but it’s not because it will cause cancer.

Cocamidopropyl Betaine:  This is a sticky liquid is part of a class of chemicals called amidopropyl betaines. These compounds consist of various fatty acids bound to amidopropyl betaine.[33] The fatty acids in Cocamidopropyl Betaine are derived from coconut oil.  It is used as a surfactant in shampoos.  It is also used to boost or stabilize foam.[34]  The fatty acid component of this molecule is lauric acid.

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Sodium Chloride:  This common salt is found in shampoos as a cleaner.   However, it can be rather irritating if it gets into your eyes.

Polyquaternium-10:  This is a conditioning agent. [36] It can reduce static electricity.  It augments the feel of hair by increasing the body and sheen or improving the texture of damaged hair.[37]

Coceth-7, PPG-1-PEG-9 Lauryl Glycol Ether, PEG-40 Hydrogenated Castor Oil:   The Coceth-7 is a mostly plant-derived carboxylic acid.  These work together as a fragrance stabilizer. The PEG‑40 It’s also a foam booster. [38]

Propylene Glycol:   The IUPAC name for this molecule is 1,2 propanediol.  It is colorless, odorless, and water-soluble.  It’s used in shampoo, because it is an effective humectant (attracts water).  It is a carrier agent for fragrances.  It can be used as an emulsifier.  It has anti-microbial and anti-fungal properties, so it can be used as a preservative.[39]    When mixed with water, PG disturbs the formation of ice, giving it an antifreeze property.[40]   MSDS for  PG lists that it can cause skin or eye irritation.[41]  There are Web sites and spam e-mails stating that propylene glycol is really industrial antifreeze and that it is the major ingredient in     brake and hydraulic fluids.   Research, however, has not found evidence of carcinogenic, mutagenic or reproductive/developmental toxicity potential to humans.[42]  Any abnormal pathology was found only in rare cases of exposures (and mainly ingestion) that exceeded recommended guidelines.

Citric Acid:  Used in shampoo to help balance the pH.[43]  It’s also used as a preservative.[44]

DMDM Hydantoin:  Common preservative for its antimicrobial properties.  IUPAC name is 1,2-demithylol-5,5 dimethyl hydantoin.[45] Formaldehyde used to be used as a preservative in cosmetics, but not often anymore.  DMDM Hydantoin is a preservative that has replaced it.  This is one of a number of preservatives that work by acting as formaldehyde donors.  So instead of adding formaldehyde itself, you add a chemical that breaks down slowly over time to release a tiny amount of formaldehyde.

Tetrasodium EDTA:  This is a composed of sodium salts.  It’s a synthetic amino acid.  It is used as a chelating agent, making hard water soft, by binding minerals to it.  In addition to cleaning your hair, surfactants in shampoo also attract metal ions found in hard water. [47]  This allows the surfactants to better do their job.

Hydrogenated coconut oil:  Coconut oil contains many nutrients, but it specifically contains lauric acid and Vitamin E. Lauric acid helps the natural nutrients to thoroughly penetrate the hair shafts all the way down to the roots and scalp. This helps in keeping both the hair and scalp moist, but not oily. Lauric acid is also an antiseptic fatty acid that works to fight off harmful bacteria and fungi.  Coconut oil also strengthens the hair thus preventing the hair from breaking (i.e. split ends) which can frequently occur when hair is repeatedly exposed processing (coloring or heating, etc.). Vitamin E is known for its antioxidant and healing properties.[49]

Lauric acid is a saturated 12-carbon molecule:

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While coconut oil is considered a saturated oil, it does have some unsaturation to it.  Why saturate an oil that is already 92% saturated?  To make the oil more stable and increase the shelf life.

Prunus Amygdalus Dulcis:  This is another name for almond oil.  It is a light, non-greasy oil.  It is a great source of vitamin E and D.  It has a sweet smell.  It contains the minerals calcium and magnesium, as well as essential fatty acids.  The highest percentage of fatty acids in sweet almond oil is oleic acid, which is an 18-carbon, omega-9, mono-unsaturated fatty acid.  Hair products with oleic acid in them help make the hair thicker and shinier.[52] The next highest fatty acid in almond oil is linoleic acid, which is an 18-carbon, omega-6, poly‑unsaturated fatty acid.

Deficiencies in linoleic acid can lead to dry hair and hair loss.[54] After the detergents in the hair have stripped the sebum and dirt, almond oil with its essential fatty acids help fortify the hair.

Macadamia Ternifolia Seed Oil: This oil (like the almond oil) is non-greasy and adds to hair softness and smoothness.[55]   This oil contains one of the highest sources of palmitoleic fatty acids, which is a 16-carbon, omega 7 fatty acid.  It’s highly valued for it’ nourishing and softening properties of the scalp and hair.[56]

PPG-9:  PPG-9 is short for Polypropylene Glycol-9 diethylmonium chloride.  It is a quaternary ammonium salt.  This helps prevent or inhibit the buildup of static electricity.  It also enhances the appearance and feel of hair, but increasing sheen or improving texture of hair that has been damaged.[57]

 Methylchloroisothiazolinone:  The IUPAC name for this molecule is   5‑Chloro-2-methyl-1,2-thiazol-3(2H)-one.  This chemical compound is used as a preservative.  It has “amazing antibacterial and antifungal properties.”[58]  It can be a skin irritant in high concentrations, but is usually dilute in shampoo formulations.[59]

Methylisothiazolinone:  This is a synthetic preservative. It’s great at controlling microbial overgrowth in water-containing solutions, such as shampoo.  It may also be added to help preserve fragrance in shampoo.  This preservative may be a skin irritant. [60]

The differences in shampoo come from other things, like conditioning agents, protectants, and other cosmetic ingredients.  Once the sebum has been removed, the cuticle is exposed and able to be damaged.  Shampoo contains things to give hair back body and shine. Silicone in shampoo can be great for coating and smoothing the hair follicle, which results in smooth, shiny, and silky hair.[61]  Silicone is a generic name for a wide variety of polymer chains with a backbone of Si‑O‑Si. They are technically known as “polysioxane.”[62]  Why use silicones in general?  They tend to last longer than natural oils and have more precise purposes, such adding shine to hair.[63]

Some people have a problem with silicone being in shampoos, as it is not water-soluble and can build up over time.  This may not be a problem for people with thick, wavy hair, but if your hair is fine, silicone buildup can be a problem.  There are, however, a few silicones that are water soluble and do a great job of protecting the hair cuticle, keeping hair smooth, and maintaining shine. Dimethicone copolyol is one such silicone.[64]  One way to make a silicone molecule soluble in water is by PEG modification (polyethylene glycol). Multiple units of ethylene glycol are added along the silicone polymer chain.  The oxygen atoms add polarity to the silicone, making them water soluble.[65]

Silicone molecules are designed to be inert and nontoxic.  Their large molecule size makes it difficult for them to be absorbed in the skin.[66]

Reading about the ingredients in typical shampoo, there’s nothing that scares me from using them on my hair, especially since I don’t leave shampoo on my hair for extended periods of time, allowing the chemicals to be absorbed in the skin.  So, why would I need a homemade shampoo?  There are a few reasons.  There are a lot of chemicals that are added to shampoo just to increase shelf life.  Making it myself would remove the “shelf life” need.  Shampoos can be expensive and sometimes, it is fun to say, “I make my own shampoo.”

How can we replace the typical shampoo bottle with a homemade version?  There are a lot of “recipes” around.  Let’s look at the “no poo” version first.

The “no poo” method for hair care is the latest fad.  Reading reported benefits of this method make it rather tempting to try:  More body, less oil, less frizz (especially for naturally curly hair), more money (less purchase of hair care products), shinier hair, less chemicals on our scalp and hair, and even decreased environmental impact.[67] How does this work?  The recommended “shampoo” ratio is 1 tablespoon baking soda to 1 cup water.  This can be mixed in a spray bottle, bowl, or ketchup-like bottle.  It is advised to not use more than the 1 tablespoon of baking soda.  The baking soda-water mixture should be mixed very well.  After wetting the hair, apply the mixture to the scalp, massaging it into the scalp and hair shaft.  Then, rinse well.

Why use baking soda as a cleaner?  The idea is that basicitiy of sodium bicarbonate (pH of 9 in water) lifts the hair follicle.  The powder that isn’t in the solution absorbs the oil.  Since it is mildly abrasive and you’re providing the manual labor, it physically scrubs the hair.

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Hair is then conditioned with an apple cider vinegar rinse.  Mix 2 tablespoons of ACV into 1 to 2 cups of water.  Rinse this over hair.    Why this?  The acetic acid in vinegar helps neutralize any remaining baking soda remaining on the scalp.  It also acts as a chelating agent, picking up minerals and keeping them from building up on your hair (thus, keeping it from looking dull). [68]

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I tried this method.  My hair tends to run a little on the dry side.  For a few weeks, this method worked great.  My hair felt clean.  However, a few weeks into it, my ends started feeling very dry.  I caved and shampooed and my hair was happy again. [69]

Why might this not work for some (like it did not for me)?  The reason could be the baking soda.  Baking soda is the common name for sodium bicarbonate with a chemical formula of NaHCO3.  Sodium bicarbonate is quite basic, with a pH of 9 (in water).[70]  According to renowned dermatologist Dr. Audrey Kunin, M.D., “The first principle of shampooing: Make sure your shampoo says it is pH-balanced and avoid those that are alkaline. Alkaline shampoos strip the hair’s natural oils and disrupt the acid mantle, causing dehydration and leading to porous, fragile hair.”[71]  There are a lot of people that use this method and it works great for them (especially people with naturally curly hair).

Is there another option to have a more natural hair care product that works more like the shampoo we know and love?  Coconut milk shampoo may be that answer. The recipe that was recommended to me is ½ cup coconut milk, 2 teaspoons extra virgin olive oil, 2/3 cup castile soap, and a few drops essential oil of your choice.  For conditioner, mix ½ cup coconut oil with ½ cup coconut milk.

The benefits of coconut oil, with vitamin E and lauric acid, in hair care products were discussed above.  Castile soap is made with fat from vegetable origin.  This soap is considered gentle on skin.  Olive oil is the traditional base, but it can be made with coconut, hemp, avocado, almond, walnut, or other oils.[72]  Extra virgin olive oil is rich in biotin, niacin, vitamins A and E and antioxidants. EVOO can be used to moisturize your scalp and condition your hair. [73]  Oleic acid is the major fatty acid in EVOO (as with almond oil).

This shampoo recipe more chemically reflects the basic structure of shampoo initially outlined.  It has the detergent component with the castile soap.  It has an emulsifier with the extra virgin olive oil.  While not as acidic as citric acid, coconut milk pH is 6.1 to 7.0[74], working as a pH stabilizer.

The US Food, Drug, and Cosmetic Act requires that each ingredient that is used in cosmetic and personal care product be tested and substantiated for safety before going to market.  Cosmetic and personal care products are regulated by the FDA (Food and Drug Administration).  Products that do not comply with regulations can have severe penalties imposed on them.   It is a federal crime to put an unsafe product on the market.[75]  Why make claims that there are harmful chemicals in our personal care products if it is not true?  It is possible that money talks.  If our shampoos have dangerous chemicals then money can be made from the creation of chemical-free shampoos.  I’m not saying this is the only reason.  There are good environmental reasons to use fewer chemicals.

 

What’s the answer?  It would depend on what your aim is.  If you’re simply looking to have clean, shiny hair, commercial shampoo could be right for you.  If you’re looking to reduce chemicals and go more natural, one of these homemade shampoos could be right for you.  For me, the fun of DIY is just in seeing what we can do to replicate commercial products.  That said, I’m confident that my shampoo isn’t going to give me cancer and I’m likely to keep using it.

 

 

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http://cosmeticsinfo.org/ingredient/ppg-9-diethylmonium-chloride-ppg-25-diethlmonium-chloride-and-ppg-40-diethylmonium  (accessed April 2014).

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http://www.dove.us/Products/Hair/Advanced-Hair-Series/Pure-Care-Dry-Oil-Shampoo.aspx  (accessed February 2014).

Sanders, Colin.  “DMDM Hydantoin.”  Personal Care Truthhttp://personalcaretruth.com/2012/02/dmdm-hydantoin/  (accessed March 2014).

“Shampoo.”  Science Toys.  http://sci-toys.com/ingredients/shampoo.html (accessed March 2014).

“Shampoo Sham.”  Snopes.com http://www.snopes.com/inboxer/household/shampoo.asp (accessed March 2014).

“Silicone Chemistry.”  Dow Corning.  http://www.dowcorning.com/content/discover/discoverchem/  (accessed March 2014).

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FOOTNOTES:

[1] http://dermatology.about.com/cs/hairanatomy/a/hairbiology.htm

[2] http://swiftcraftymonkey.blogspot.com/2010/05/chemistry-of-your-hair-shampoo.html

[3] http://dermatology.about.com/cs/hairanatomy/a/hairbiology.htm

[4] http://www.organicgreentouch.com/hair-facts

[5] http://dermatology.about.com/cs/hairanatomy/a/hairbiology.htm

[6] http://lifestyle.iloveindia.com/lounge/facts-about-hair-11117.html

[7] http://www.loc.gov/rr/scitech/mysteries/grayhair.html

[8] http://www.loc.gov/rr/scitech/mysteries/grayhair.html

[9] http://www.webmd.com/beauty/hair-nails/20090225/why-hair-goes-gray

[10] http://en.wikipedia.org/wiki/File:Cystine-skeletal.png

[11] http://www.economicexpert.com/a/Sulfur:bridge.htm

[12] http://beautysupply.about.com/od/chemicalhairtreatments/g/Disulfide-Bonds-Definition.htm

[13] http://swiftcraftymonkey.blogspot.com/2010/05/chemistry-of-your-hair-shampoo.html

[14] http://www.livescience.com/3659-great-shampoo-sham.html

[15] http://www.randomhistory.com/2008/07/19_shampoo.html

[16] http://www.randomhistory.com/2008/07/19_shampoo.html

[17] http://www.hair-heads.co.uk/hair-shampoo/shampoo-history.php

[18] http://www.madehow.com/Volume-3/Shampoo.html

[19] http://www.chagrinvalleysoapandsalve.com/idascorner/soaphowworks.aspx

[20] http://chemistry.about.com/od/howcleanerswork/a/How-Shampoo-Works.htm

[21] http://www.hairfinder.com/hairquestions/shampoohow.htm

[22] http://chemistry.about.com/od/cleanerchemistry/a/makeshampoo.htm

[23] http://www.discoverhealthandwealth.com/toxic-ingredients.html

[24] http://www.eng.buffalo.edu/Courses/ce457_527/ce457_pro/g7_doc.htm

[25] http://www.sixwise.com/Newsletters/2009/November/11/How-Many-Dangerous-Chemicals-are-in-Your-Shampoo.htm

[26] http://www.naturalnews.com/042390_cancer-causing_chemicals_shampoos_personal_care_products.html#

[27] http://www.discoverhealthandwealth.com/toxic-ingredients.html

[28] http://www.dove.us/Products/Hair/Advanced-Hair-Series/Pure-Care-Dry-Oil-Shampoo.aspx

[29] http://swiftcraftymonkey.blogspot.com/2010/04/surfactants-alkyl-ether-sulfates.html

[30] http://www.livestrong.com/article/159171-the-disadvantages-of-sodium-laureth-sulfate/

[31] http://www.snopes.com/inboxer/household/shampoo.asp

[32] http://science.howstuffworks.com/environmental/green-science/sodium-lauryl-sulfate1.htm

[33] http://cosmeticsinfo.org/ingredient/cocamidopropyl-betaine

[34] http://www.wisegeek.com/what-is-cocamidopropyl-betaine.htm

[35] http://en.wikipedia.org/wiki/File:Cocamidopropyl_betaine2.png

[36] http://www.makingcosmetics.com/Polyquaternium-10-p147.html

[37] http://cosmeticsinfo.org/ingredient/polyquaternium-10

[38] From sales representative from Ross Organics, Aaron Peterson (my neighbor)

[39] http://www.naturallycurly.com/curlreading/curl-products/curlchemist-the-truth-and-fiction-about-propylene-glycol/

[40] http://www.livestrong.com/article/116991-properties-propylene-glycol/

[41] http://www.mono-propylene-glycol.com/upfiles/file/Propylene-Glycol-MSDS.pdf

[42] http://www.ingentaconnect.com/content/apl/btxc/2013/00000043/00000004/art00003

[43] http://sci-toys.com/ingredients/shampoo.html

[44] http://cosmeticsinfo.org/ingredient/citric-acid-and-its-salts-and-esters

[45] http://www.wisegeek.com/what-are-the-uses-of-dmdm-hydantoin.htm

[46] http://personalcaretruth.com/2012/02/dmdm-hydantoin/

[47] http://health.howstuffworks.com/skin-care/cleansing/products/tetrasodium-edta-in-cleansers.htm

[48] http://en.wikipedia.org/wiki/File:Propylene_glycol_chemical_structure.png

[49] http://www.usesforcoconutoil.org/Coconut_Oil_For_Hair.html

[50] http://upload.wikimedia.org/wikipedia/commons/7/7f/Lauric_acid.png

[51] http://upload.wikimedia.org/wikipedia/commons/b/b1/Oleic-acid-based-on-xtal-1997-2D-skeletal.png

[52] http://www.naturalwellbeing.com/learning-center/Oleic_Acid

[53] http://en.wikipedia.org/wiki/File:LAnumbering.png

[54] http://www.truthinaging.com/ingredients/linoleic-acid

[55] http://usa.weleda.com/ingredients/macadamia-ternifolia.aspx

[56] http://chemical-sensitivity.info/Chemical-Free-Shampoo-Benefits.html

[57] http://cosmeticsinfo.org/ingredient/ppg-9-diethylmonium-chloride-ppg-25-diethlmonium-chloride-and-ppg-40-diethylmonium

[58] http://www.naturalwellbeing.com/learning-center/Methylchloroisothiazolinone

[59] http://www.wisegeek.com/what-is-methylchloroisothiazolinone.htm

[60] http://www.naturalwellbeing.com/learning-center/Methylisothiazolinone

[61] http://www.hairfinder.com/hair3/silicon-shampoo.htm

[62] http://www.dowcorning.com/content/discover/discoverchem/

[63] http://www.ehow.com/about_5659828_dimethicone-vs_-silicone.html

[64] http://www.naturallycurly.com/curlreading/curl-products/whats-the-scoop-on-silicones

[65] http://www.naturallycurly.com/curlreading/products-ingredients/water-soluble-silicones/?page=2

[66] http://www.ehow.com/about_5659828_dimethicone-vs_-silicone.html

[67] http://www.crunchybetty.com/no-poo-to-you-too

[68] http://allaboutbakingsoda.blogspot.com/2010/05/structure-of-baking-soda.html

[69] http://en.wikipedia.org/wiki/File:Acetic-acid-2D-flat.png

[70] http://www.alkalinephdiet.com/baking-soda-ph/

[71] http://www.futurederm.com/2012/06/20/3-reasons-why-baking-soda-and-apple-cider-vinegar-destroy-your-hair-and-what-to-use-instead/

[72] http://www.wisegeek.org/what-is-castile-soap.htm

[73] http://www.livestrong.com/article/167093-extra-virgin-olive-oil-as-a-hair-conditioner/

[74] http://www.engineeringtoolbox.com/food-ph-d_403.html

[75] http://cosmeticsinfo.org/get-the-facts

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