JOURNAL OF COSMETIC SCIENCE 584 In the second paper of our series (3), an attempt was made to show some integration of the different factors (Introduction section) involved in hair breakage, rather than to sug- gest that one precludes the other as suggested by the following statement in the synopsis: “Extension or impacting hair fi bers with fl aws or damaged hair sections such as damaged wrapped ends produces short fi ber fragmentation, while longer segment breaks may be produced in fi bers with natural fl aws (19) such as fi ber twists, cracks or badly abraded (3,10,13,14) or chemically weakened hair or even knots (3,4).” (Reference citations in this quotation refer to references in the current paper.) CONCLUSION The phenomenon of hair breakage is a complex phenomenon involving multiple factors including progressive damage and the progressive propagation of fl aws within the fi ber as stated by Evans and Park, but more importantly it involves high localized stresses created in tangles. We believe that the literature clearly shows that the primary factors involved in hair breakage are the occurrence of tangles created by combing or brushing where one or more hair fi bers are severely bent around at least one other hair. Therefore, high local- ized stresses are created by impact or pulling through that tangle. As a result, one or more hair breaks, either with or without fl aws, under this condition. Other variables are clearly involved to determine the actual number of broken hairs and the type of fractures. These variables include hair type (primarily curvature), hair condition (treatments and wear), relative humidity or water content of the hair, and the specifi c grooming device as ex- plained in the Discussion section. Brushing and combing certainly play a role in weaken- ing hair, but they are unlikely to lead to pure fatigue breaks as claimed by the authors, especially under the low load levels experienced by the fi bers. REFERENCES (1) T. A. Evans and K. Park, A statistical analysis of hair breakage. II. Repeated grooming experiments, J. Cosmet. Sci., 61, 439–456 (2010). (2) A. C. Brown and J. A. Swift, Hair breakage: The scanning electron microscope as a diagnostic tool, J. Soc. Cosmet. Chem., 26, 289–297 (1975). (3) C. Robbins, Hair breakage during combing. II. Impact loading and hair breakage, J. Cosmet. Sci., 57, 245–257 (2006). (4) N. P. Khumalo, R. P. R. Dawber, and D. J. P. Ferguson, What is normal black African hair? A light and scanning electron-microscopic study, J. Am. Acad. Dermatol., 43, 814–820 (2000). (5) C. Robbins, in Chemical & Physical Behavior of Human Hair, 4th Ed. (Springer Verlag, Berlin, Heidelberg, New York, 2002), pp. 399–401. (6) C. Robbins, Ibid, pp. 398–399. (7) C. M. Pande, L. Albrecht, and B. Yang, Hair photoprotection by dyes, J. Cosmet. Sci., 52, 377–390 (2001). (8) Y. K. Kamath, S. Hornby, and H. D. Weigmann, Effect of chemical and humectants treatments on the mechanical and fractographic behavior of Negroid hair, J. Soc. Cosmet. Chem., 36, 39–52 (1985). (9) R. Beyak et al. Elasticity and tensile properties of human hair. II. Light radiation effects, J. Soc. Cosmet. Chem., 22, 667–678 (1971). (10) C. Robbins and Y. K. Kamath, Hair breakage during combing. III. The effects of bleaching and condi- tioning on short and long segment breakage by wet and dry combing of tresses, J. Cosmet. Sci., 58, 477–484 (2007). (11) J. Epps and L. J. Wolfram, Letter to the Editor, J. Soc. Cosmet. Chem., 34, 213–214 (1983). (12) T. A. Evans, Fatigue testing of hair—A statistical analysis of hair breakage, J. Cosmet. Sci., 60, 599–616 (2009).

HAIR BREAKAGE 585 (13) Y. K. Kamath and H. D. Weigmann, Fractography of human hair, J. Appl. Polym. Sci., 27, 3809–3833 (1982). (14) C. Robbins, H. D. Weigmann, S. Ruetsch, and Y. K. Kamath, Failure of intercellular adhesion in hair fi bers with regard to hair condition and strain conditions, J. Cosmet. Sci., 55, 351–371 (2004). (15) C. Robbins and C. Reich, Prediction of hair assembly characteristics from single fi ber properties. Part II. The relationship of fi ber curvature, friction, stiffness and diameter to combing behavior, J. Soc. Cosmet. Chem., 37, 141–158 (1986). (16) Y. K. Kamath and H. D. Weigmann, Measurement of combing forces, J. Soc. Cosmet. Chem., 37, 111– 124 (1986). (17) C. Robbins and Y. K. Kamath, Hair breakage during combing. IV. Brushing and combing of hair, J. Cosmet. Sci., 58, 629–636 (2007). (18) Unpublished data, TRI/Princeton. (19) Y. K. Kamath, S. B. Hornby, and H. D. Weigmann, Mechanical and fractographic behavior of Negroid hair, J. Soc. Cosmet. Chem., 35, 21–43 (1984).