The cuticle of hair (the outer covering of “scales” over the inner fiber) is very rich in protein, especially cystine. The epicuticle (a protein and lipid-rich layer covering the cuticles) is rich in amino acids (smaller components of proteins). To temporarily repair damaged hair, protect porous hair and add body to fine/thin hair, look for products containing hydrolyzed wheat, soy, quinoa and keratin proteins and amino acids to add cystine to the cuticle for shine and moisture retention.