differently treated relaxed hair was significant: break stress drasti- cally decreased with increased humidity. For example, the break stress of relaxed hair control at 80% was lower by 35.3% in com- parison with that at 20% RH. Moreover, the higher environmental humidity significantly affected the differences between hair treatments as well. The most notable were the following: break stress of virgin hair, mid- and high-MW peptides treated relaxed hair was higher than that of control relaxed hair by 130.9%, 40.0% and 31.6%, respectively (all statistically significant differ- ences). Figure 7 Young’s modulus measured at 20% and 80% RH as a function of treatment and hair condition (means Æ standard errors). At 20% RH, results that are statistically different in comparison with relaxed hair control (DI water) are labelled with the letter a, and results that are significantly different from virgin hair control (DI water) are labelled with the letter b. At 80% RH, results that are statistically different in comparison with relaxed hair control (DI water) are labelled with the letter c, and results that are significantly different from virgin hair control (DI water) are labelled with the letter d. Table 1 The treatment effect on the premature breakage (number of prematurely broken fibres per 50 tested fibres) Relaxed Hair DI Water Relaxed Hair 1% Leucine Relaxed Hair 1% Low-MW Keratin Peptide Relaxed Hair 1% Mid-MW Keratin Peptide Relaxed Hair 1% High-MW Keratin Peptide Virgin Hair DI Water p Chi-Squared Test 20% RH 15 19 15 6 5 12 0.005 80% RH 10 6 9 3 1 4 0.028 Figure 8 Break stress measured at 20% and 80% RH as a function of treatment and hair condition (means Æ standard errors). At 20% RH, results that are statistically different in comparison with relaxed hair control (DI water) are labelled with the letter a, and results that are significantly different from virgin hair control (DI water) are labelled with the letter b. At 80% RH, results that are statistically different in comparison with relaxed hair control (DI water) are labelled with the letter c, and results that are significantly different from virgin hair control (DI water) are labelled with the letter d. 8 © 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. "" Q. (/) :::, :J '8 ~ (/) ·o, C :::, ~ 1l [l._ ~ (/) (/) ~ ii5 . 1l ~ co 4.50E+09 4.00E+09 3.50E+09 3.00E+09 2.50E+09 200.0 150.0 100.0 50.0 0.0 a b b d d d n n n □ 20% RH a d n cd n □ 80% RH C n Relaxed Hair Relaxed Hair Relaxed Hair Relaxed Hair Relaxed Hair Virgin Hair DI DI Water 1% Leucine 1% Low Mw 1% Mid Mw 1% High Mw Water Keratin Keratin Keratin Peptide Peptide Peptide □ 20% RH □ 80% RH a ab ab b b ab cd cd ~ d d d n n n n Relaxed Hair Relaxed Hair Relaxed Hair Relaxed Hair Relaxed Hair Virgin Hair DI Water DI Water 1% Leucine 1% Low Mw 1% Mid Mw 1% High Mw Keratin Keratin Keratin Peptide Peptide Peptide