from each group was measured as described above. Fig. 1 presents the cross-sectional area of hair with different treatments as indi- cated. Statistical analysis showed that cross-sectional areas of hair treated with 1% low-MW keratin peptide and 1% leucine-treated hair were significantly higher than that of both virgin and relaxed hair controls (11.7% and 11.0%, respectively, higher than relaxed hair control). These results suggest that low-MW actives effectively penetrated into the damaged hair cortex. As we were not able to evaluate mid- and high-MW peptide pen- etration using diameter measurements, we used fluorescence Figure 2 Cross-sections of Afro-textured relaxed hair soaked for 3 h in dye solution that was filtered via centrifugal filter to remove free dye at low (209, top) and high (409, bottom) magnification. Figure 3 Cross-sections of Afro-textured relaxed hair soaked in labelled mid-MW keratin peptides for 3 h at low (209, top) and high (409, bottom) magnifica- tion. 4 © 2020 The Authors. International Journal of Cosmetic Science published by John Wiley & Sons Ltd on behalf of Society of Cosmetic Scientists and Societe Francaise de Cosmetologie International Journal of Cosmetic Science, 1–12 Larger hydrolyzed keratins reduce hair breakage E. Malinauskyte et al.