Sunday, August 7, 2011

Amino Acids in Hair Products

Updated: March 2019.

What Are Amino Acids:
Amino acids are very small molecules, they’re not even “proteins” on their own, they’re the constituents of proteins formed from an amine group (nitrogen-containing, and all things proteinaceous contain nitrogen), a carboxylic acid group (carbon, hydroxide or “OH” and oxygen) and a side chain with a varied number of carbons, nitrogens, hydrogens, occasionally sulfur. To have a protein, you put these amino acids together.©Science-y Hair Blog 2013

Where Are They:
In hair, there are many amino acids (one source I have lists 20). The cuticle of hair – it’s multi-layered outer coating of “scales,” contains more amino acids than in the inner parts of the hair fiber - partly because proteins break down into amino acids and there is always protein being broken down at the cuticle. The outermost layer of cuticle (which can be missing at the ends of very long or damaged hair) contains more cysteine forming cross-links with other proteins – creating a strong, resilient outer cuticle. Cysteine is a sulfur-rich amino acid. I imagine this like “cuticle glue.”  Also in high amounts in the cuticle are glutamic acid, proline and valine.
In the epicuticle (a protein-heavy, lipid-rich covering over the cuticle) there are large amounts of glutamic and aspartic acids and lysine.©Science-y Hair Blog 2013

Amino acid content in hair increases with exposure to UV light and to bleaching chemicals or “retexturizing” (permanent waves, chemical relaxers) – as breakdown products from the hair proteins resulting from these processes.

Do Amino Acids Stay on My Hair?©Science-y Hair Blog 2013
You may have heard that amino acids simply rinse away when they are included in a shampoo or conditioner. This is not entirely true. If you apply amino acids to hair mixed in only water, hair will take up as much as it can (there is a point at which the hair will stop adsorbing amino acids when it reaches equilibrium with the solution into which you’ve placed it). But if amino acids are present in a formula (like a conditioner) including cationic surfactants, adsorption of amino acids becomes more difficult because they interact with the other ingredients. In general, studies have shown that the addition of amino acids to a formula helps damaged hair regain it’s hydrophobicity or it’s water-repellent quality which means that amino acids help fill in porosities (gaps in the cuticle). Healthy, undamaged hair is also hydrophobic/water repellent. Amino acids can also strengthen and moisturize the hair because of their water-attracting habit.

Which Amino Acids Work Well (or “should” work well):©Science-y Hair Blog 2013
Of those tested, arginine was strongly attracted to hair. Histidine and phenylalanine improved the strength of hair, but only histidine, phenylalanine, glutamic acid, arginine, alanine, and isoleucine, were studied in the reference I am using. Many were left out!

Usually one finds amino acids listed as “silk amino acids” or "methionine" or “wheat amino acids.” Which should you look for?
Here is what I can find from manufacturers’ descriptions of amino acid additives regarding their constituent amino acids which are present at the highest percentages (they do contain a variety of other amino acids). The italics refer to amino acids which occur in high amounts in the cuticle and epicuticle of hair.©Science-y Hair Blog 2013

Silk amino acids: alanine, glycine and serine
Wheat amino acids: cysteine, glutamic acid
Oat Protein and derivatives: glutamic acid, aspartic acid, proline, alanine
Soy protein and derivatives: phenylalanine, tyrosine, leucine
Keratin amino acids: cysteine, serine, glutamic acid
Cysteine - check out those sulfurs!

Interior or exterior of hair? Amino acids tend to have molecular weights less than 200 g/mol. This is small enough to penetrate into the cortex of hair (and into skin as well). Amino acids can move into the hair's cuticle to help retain moisture for good hydration.cience-y Hair Blog 2013

Other notes: If you are allergic to any of these ingredients (like wheat) or have an intolerance which causes severe physical symptoms, you may also need to avoid the hydrolyzed versions of the proteins. 13

Does it really work to try to “replace” amino acids in the hair with amino acids from an outside source? Difficult to say. Whether it is because the amino acid from a hair product takes on a functional role (literally replaces that which was lost and starts playing the same role) or just plays a supporting role, they are effective moisturizers and therefore do have benefits in rinse-off and leave-in products.

Journal of Cosmestc. Science, 58, 347-357 , 2007
Hair and amino acids: The interactions and the effects
E. Oshimura, H. Abe, and R. Oota

Chemical and Physical Behavior of Human Hair 
Robbins, 1994. 3rd Ed. Springer-Verlag, New York


  1. So if my hair doesn't like proteins in hair products it also won't like amino acids?

  2. Love your blog!! Fantastic info. I have thick coarse highlighted (blonde) hair that is dry.
    Been trying to go silicone free (is this a good idea or not?). I thought silicone free I could see true health of my hair. I'm confused which small protein product to try.. All the oils and deep conditioners I have tried (protein free) don't seem to help. Very tangled hair unlike when I used Wen but scalp didn't feel clean with wen but it was nice because it didn't tangle up my hair. Am I doing more damage going without silicones? I'm having hard time finding only water soluble silicone products.
    Also wondering if I need a small shot of protein. My hair feels stretchy when wet and still dry when dry (even after leave ins like Phyto-7, Giovanni leave in, etc). And still tangles more when dry without those silicones I used to not pay attention to. Thanks for your advice!! Go back to silicones? Or try a hydrolyzed protein conditioner? Trying to find one without too many. I have one that has oats, horsetail, nettles and orange wax among other things (supposed to be "natural") but when wet my hair feels weird with it.
    Sorry for so long winded!! :-)
    Please keep up the great work - so valuable and informative!! Best

    1. Hello Amy,
      I'm going to direct you to this post about creating a hair care routine and handling problems:
      If your hair is feeling worse with conditioners containing protein, then your hair may need protein only once in a while, not every wash day.
      You might need to shop around for conditioners too, a good conditioner will help your hair feel slippery and smooth, even without silicones. Giovanni 50:50 or Giovanni Tea Tree Triple Treat might be good choices if you like Giovanni. Tresemme Undone and Tresemme Botanique conditioners are popular products that aren't necessarily natural, but easy to find. Sometimes the deep conditioners you'll find contain ingredients that may not be suitable to your hair. Some people's hair does very well with things like shea butter and coconut oil and glycerin. Other people's hair doesn't do well with those ingredients. Good luck! W

  3. I'm definitely experiencing hair breakage. My hair is very coarse and thick. It's become stiff and is breaking at the point where my relaxed hair meets my natural hair. I was told to get a clarifying shampoo to combat the extra protein overload. It's gotten better with cowashing with Aussie's mega moist conditioner.

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