To investigate the penetration of amino acids and hydrolyzed protein derived from eggwhites (HEWP) into keratin fibers, the structure of cross-sectional samples at various depths of virgin white human hair treated with L-phenylalanine (Phe) and bleached black human hair treated with HEWP was directly analyzed without isolating the cuticle and cortex using Raman spectroscopy. The hydrophobic amino acids clearly penetrated into the virgin white human hair, while hydrophilic amino acids did not penetrate at all. The Phe hydrophobic amino acid content at various depths of the virgin white hair increased by performing the Phe treatment (at 50 degrees C for 16 h), indicating that Phe deeply penetrated into the virgin human hair. Also, the disulfide (-SS-) and random coil contents at various depths of the bleached human hair increased by performing the HEWP treatment, indicating that HEWP also deeply penetrated into the bleached human hair. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 2680-2689, 2011