Everything I have read about amino acids in hair products has been conflicting. So I did a little digging and here’s what I found out.©Science-y Hair Blog 2013
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 cystine forming cross-links with other proteins – creating a strong, resilient outer cuticle. Cystine 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: cystine, glutamic acid
Oat Protein and derivatives: glutamic acid, aspartic acid, proline, alanine
Soy protein and derivatives: phenylalanine, tyrosine, leucine
I cannot find a reference determining whether amino acids penetrate the hair shaft beyond the cuticle, but the cuticle is where much damage takes place and it is the structure meant to protect the inner hair fiber, so even if its effects are limited to the cuticle, that’s still a very good thing.©Science-y Hair Blog 2013
Which amino acids to look for:
Keratin is made from hair or other keratin-containing animal sources. It most closely resembles the amino acid content of hair, so this seems like a good choice. The other amino acids listed above are also good choices, especially wheat, oat, and soy, as noted in italics because they contain higher amounts of cystine, glutamic acid, aspartic acid and proline.
Some people cannot use much protein on their hair – bleached hair needs protein, but it grabs on to it more readily and loses it more readily than unbleached hair and this may cause an unpleasant result. Very coarse hair (meaning hairs with a large diameter) may not respond well to protein because of its “stiffening” effect – making hair feel dry and rough and possibly causing breakage. Some silky, fine, healthy hair gets too silky and flat with too much protein.©Science-y Hair Blog 2013
If you are allergic to any of these ingredients (like wheat) or have an intolerance which causes severe physical symptoms, you also need to avoid the hydrolyzed versions of the proteins. They are smaller than the whole protein, so their ability to act as allergens may be reduced, but for very sensitive persons, they still present a problem and are best avoided.©Science-y Hair Blog 2013
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