HAIR FIBER HYDRATION 533 0.5 0.4 '• 0.3 ß *-, 0.2. 0 • OA (.3 0.0 --•--REFERENCE ---,G-- TREATMENT • TREATMENT = TREATMEN --O--TREATMENT4 I 510 I I I ' I ' I 0 100 150 200 250 300 Reaction Temperature øC Figure 6. CO 2 weight percentage observed in the vapor from the hair heat treatment. A comparison of treatments 1 and 2 shows that treatment 2 provides both a higher AHvap value (267.79 J/g) and a higher percentage of water (12.82%) than treatment 1 (AHvap -- 209.96 J/g and 7.43% water). The results for treatments 3 and 4 show that treatment 3 provides a lower AHvap value (192.49 J/g), but a higher water percentage (16.73%) than treatment 4 (230.91 J/g and 12.85%, respectively). The DSC measurements show the extent to which heated hair fibers are protected from water loss, while GC measures the water content in hair fiber. Depending on its com- position, the formula may simply add water to the hair fibers and/or protect them from water loss (for example, by forming a film around the fiber), which may or may not result in proportional DSC and GC values. DSC is an effective technique for evaluating the thermal behavior of water present in hair: it allows the determination of the bonding energy of water in the hair fiber. The amount of water, however, cannot be determined directly by DSC. GC is a reliable technique for the quantification of water present in hair, and was therefore used as a complementary tool to DSC for the purpose of this study. Hair moisturizers can increase the amount of water in the hair fiber and/or form a barrier that hinders water desorption. Therefore, the association of these two analytical techniques proved particularly useful in the evaluation of hair fiber hydration. Because the amount of consumed energy provides an indication of the level of protection, the DSC data also show that this technique can be applied to evaluate the thermal protection properties of hair fibers. During the consumer research, the following attributes of moisturized hair were most frequently mentioned: softness, gloss, gliding feel, and silkiness. These attributes do not depend exclusively on hydration (7). The panelists did not identify significant differ- ences between treatments 1 and 2 and control (p = 0.1722), nor were they able to identify differences between treatments 3 and 4 and control (p = 0.0643), which indi- cates that consumer testing is inadequate to evaluate hair hydration. Sensory analysis is

534 JOURNAL OF COSMETIC SCIENCE important for the evaluation of other attributes perceived by consumers, such as softness and gloss. Therefore, the results of subjective evaluations, which involve individual psychological and physiological differences (18,19), do not provide the necessary accu- racy to determine the level of hydration offered by hair products. Consequently, the assessment and quantification of water in hair by means of DSC and GC techniques become essential for substantiating the moisturizing properties of hair products in their development stage. CONCLUSIONS DSC is an effective technique for the evaluation of the thermal behavior of water in hair since it allows for determining the bonding strength of water to hair fibers. GC is a specific, sensitive, and accurate technique for the quantification of the water present in hair fibers. Sensory evaluations are inadequate for the assessment of the hydration levels provided by different cosmetic hair products. The association of DSC and GC techniques is appropriate, accurate, practical, and readily available, and yields accurate results for water content in hair. Because sensory evalua- tions have shown that consumer perceptions of moisturized hair are confused with other attributes that do not depend exclusively on hair fiber hydration, obtaining this type of analytical evidence is an essential requirement. ACKNOWLEDGMENTS The authors gratefully acknowledge the support provided by "O Boticirio" and the following Brazilian funding agencies: CNPq, CAPES, CEPID, FINEP, and FAPESP. REFERENCES (9) (10) (1) O. Freis, A. Charbonnelle, J. C. Audonneau, V. Gillon, and G. Pauly, Hair care active ingredients: Cosmetics properties and methods for evaluating their efficacy, www. sfc-online. com. (2) S. P. Chahal, N. I. Challoner, and R. T. Jones, Moisture regulation of hair by cosmetic proteins as demonstrated by dynamic vapor sorption: The novel efficacy testing technique, IFFCC Magazine, 3, 2 (2000). (3) J. H. Riedel, Use of modern efficacy tests for hair, Advances in Hair Research (IFFCC, 2000). (4) O.G. Marrisen, S. Grinnes, and E.S. Kongshaug, Ambient relative humidity and the electrical properties of human hair, Proc. Ann. Conf Eng. Med. Bid., 15 (1993). (5) J. L. Leveque, J. C. Garson, and G. Boudouris, Water in keratin: Electrical conductivity measurements, C.R. Acad Sci., D., 288, 22 (1979). (6) R. Drozdenko, C. Weinstein, and S. Weintein, Application of electrical hygrometric measures to the evaluation of hair moisturizing products, J. Soc. Cosmet. Chem., 43, 179-186 (1992). (7) C. R. Robbins, Chemical and Physical Behavior of Human Hair, 3rd ed. (Springer-Verlag, New York, 1994). (8) S. D. O'Connor, K. L. Komisarek, and J. D. Baldeschwieler, Atomic forces microscopy of human hair cuticles: The microscopic study of environmental effects on hair morphology,J. Invest. Dermatol., 105, 1 (1995). K. Martin, Near-Infrared reflectance for evaluation of chemical, physical and sensory properties of hair in the salon, IFSCC. P026 (1998). T.V. Marcelo, Application of a tensile-strength test method to the evaluation of hydrating hair products, Int. J. Cosmet. Sci., 20, 4 (1998).