To explore the effect of different hydrolyzed keratin on leave-on hair masks

Background: Keratin is the main ingredient of hair fiber, with more than 80% of content [1-4]. Hydrolyzed keratin has restorative effect for hair, mainly used in the wash-off products in the past while less in the leave-on products. As karatin with different molecular weights contributes differently to sensory and restorative effect, it is very important to maximize restorative effect but choose right sensorial karatin. Moreover, keratin in leave-on products works more effective on resorative effect than rinse-off products. Additionally, many hair repair materials are not suitable to be used in leave-on products, because they easilylead the hair too hard. Therefore, in this study, the effects of different molecular weights of keratin on the restorative and sensory effects of leave-on hair masks were investigated.
Experiment 1: Hydrolyzed keratin solutions with different molecular weights were added to the formulation of same leave-on hair mask to investigate the restorative effect of the different solutions on the hair and the sensory evaluation after using the product.
Formulation A: 0.25% hydrolyzed keratin with molecular weight 1800-2000 Da;
Formulation B: 0.25% hydrolyzed keratin with molecular weight 1000 Da;
Formulation C: 0.25% hydrolyzed keratin with molecular weight 10000 Da;
Formulation D: 0.125% hydrolyzed keratin with molecular weight 400 Da compounded with 0.125% hydrolyzed keratin with molecular weight 10,000;
Formulation E. 0.375% hydrolyzed keratin with molecular weight 10,000.
Experiment 2: 5 bunches of hair from the same batch were taken and treated equally. The hair was observed with a 1000x microscope before applying the hair mask. Then, 0.5 g of the corresponding hair mask was applied evenly to each hair bunch, and then keep for 8h to observe the hair mask's repairing effect on the hair scales with a 1000x microscope.
Experiment 3. Testing of hair diameter and pulling strength: After the same treatment, the cross-sectional area and pulling strength of each hair were measured.
Experiment 4. Sensory evaluation: 6 bunches of hair from the same batch were taken and evaluated by 20 people based on the untreated hair bunch. They were finger combing, smoothness, refreshing, moistness, strength elasticity, softness and preference, respectively.
Results:
1. The results of experiment 2, the smoothing and repairing effect on hair scales from the microscopic results, D=E>A>C>B
2. The result of experiment 3, the pulling strength: E>D>C>A>B.
3. The result of experiment 4, overall score of sensory effect: D>E>A>C>B. The scope of D got the high score in all terms especial in the finger combing. In formula E, the scope is much lower than Cand D in the terms of finger combing and strength elasticity effect. The evaluation result of formula B were almost consistent with control group.
Conclusion: From the results of Experiment 2 to 4, the combination of the hydrolyzed keratin with molecular weight 400 compounded and hydrolyzed keratin with molecular weight 10,000 has the best repairing and sensory effect on hair. Especially in the key point of sensory effect, formula D got the higher scope than other formula. The hydrolyzed keratin with molecular weight 400 can penetrate well into the hair core and repairs the hair . The hydrolyzed keratin with molecular weight of 10,000 forms a protective film on the surface of the hair. But the hydrolyzed keratin with 10000 molecular weight could not added more than 0.25%. In formula E, when add 0.375%, the scope is much lower than Cand D in the terms of finger combing and strength elasticity effect. Hydrolyzed keratin with medium molecular weight, as in formula B, it couldn’t well into the hair core and also couldn’t forms a protective film on the surface of the hair. So whether in restorative effect or sensory effect, it couldn’t got the good scope.
In leave-on hair mask, the sensory effect is most important. Therefore, the combination of the hydrolyzed keratin with molecular weight 400 compounded and hydrolyzed keratin with molecular weight 10,000 is the best choice in leave-on hair mask .
Key words: Hydrolyzed keratin, molecular weight, sensory effect, leave-on, restorative effect