Currently, there are several hair products - shampoos, conditioners, treatment products, among others - that use proteins or amino acids in their compositions. But do you know the importance of these ingredients for hair?
Some of the benefits attributed to proteins are described as improved strength, increased volume, and conditioning. And how and why do these ingredients manage to enhance these attributes? For this, we need to understand what proteins are, what hair is, and how they interact.
Proteins are macromolecules formed by a long chain of amino acids linked together by peptide bonds. These bonds can be "broken," creating hydrolyzed proteins, peptides, or amino acids. Each protein has a unique composition of amino acids that influences its properties. Amino acids can be cationic, anionic, polar, and non-polar, which leads proteins to exhibit positive and negative charges, displaying amphoteric behavior.
Proteins have a high chemical affinity for hair, as hair is predominantly proteaceous, made of keratin. Hair fibers have an isoelectric point at approximately pH 3.8; above this value, hair fibers become more negative, and below this value, more positive.
Hair is composed of cuticle, cortex, medulla, and intercellular cement. The cuticle is the outer region of the strands responsible for the chemical protection of the strands and is made up of proteinaceous and amorphous material with a high content of the amino acid cysteine. The cortex, the internal and crystalline region of the strands, is the structural element of hair responsible for mechanical and elastic properties, also containing cysteine in its composition. The cement is mainly composed of fatty acids and ceramides and is responsible for the adhesion of cuticular and cortical cells. The medulla is the central region of the strand that may or may not be present and does not yet have a specific determined function.
And how do the interactions of proteins and/or amino acids with hair occur? Amino acids containing sulfur (cystine and its oxidized form cysteine) can covalently bond with the cysteine residues of hair, forming disulfide bonds (S-S), which confer, among other properties, high resistance to hair fibers. Cationic amino acids like lysine and arginine bind through electrostatic interactions; amino acids containing amino and carboxylic groups (glutamic and aspartic acid) bind through hydrogen bond formation. Several factors can interfere with these interactions, such as: molar mass and conformation of the proteins, pH, solvent, and ionic strength of the medium.
Knowing that proteins have a high affinity for hair, the conditioning potential of these ingredients is widely explored. High molar mass proteins can form films, adhere to cuticles, and usually influence properties such as shine, lubricity, frizz, and softness. On the other hand, low molar mass proteins and amino acids can penetrate the cuticles and reach the cortex, improving properties of stress-strain such as strength and elasticity of the strands.
In addition, proteins within a cosmetic formulation can be used as protection against adverse effects of detergency, chemical treatments, and bleaching. They are also used for stabilizing foams and for emulsifying and detergent properties.
Today, proteins extracted from various sources are available: animal, plant, and marine, sold in hydrolyzed form (totally or partially) and quaternized. The latter, due to their positive charges, enhance interactions with hair fibers that have negative charges.
And how do we lose the proteins from our hair, and what damage will we have with these changes? Daily care, such as washing and combing, the application of high temperatures - flat irons and hair dryers - and the performance of relaxers, perms, and dyes cause damage to hair. Among them, one can mention alterations of disulfide bonds or solubilization and loss of peptides, amino acids, and fatty acids, leading to the formation of split ends, breakage, tangling of strands, and loss of shine.
It is recommended to periodically use good conditioning agents, such as proteins, to reduce these damages. And how can we bring more benefits with the use of these ingredients? Knowing that each hair has a different chemical composition, thinking about the theme of biomimetics and molecular biology techniques, could we develop a personalized protein to be applied to each type of hair that restores the damage, bringing back the beauty of your strands? What other development paths can be envisioned within this theme? Share!
Adriana Fregonesi is a chemist graduated from UNICAMP and has a PhD in Science with an emphasis on interface and surface chemistry. She is a collaborator at Natura and is currently in the Cosmetic Specialties Unit.
Contact: adrianafregonesi@natura.net
REFERENCES
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