J. Cosmet. Sci., 62, 579–585 (November/December 2011) 579 Hair breakage by combing and brushing—A comment on: T. A. Evans and K. Park, A statistical analysis of hair breakage. II. Repeated grooming experiments, J. Cosmet. Sci., 41, 439–456 (2010) Y. K. KAMATH and C. ROBBINS, Kamath Consulting Inc., 11 Deer Park Drive, Monmouth Junction, NJ 08852 (Y.K.K.), and 12425 Lake Ridge Circle, Clermont, FL 34711 (C.R.). Accepted for publication June 9, 2011. Synopsis Literature dealing with the mechanisms of hair breakage in combing and brushing published so far has been reviewed as a background for the critical evaluation of the method and data analysis of the paper “Statistical Analysis of Hair Breakage. II” by Evans and Park (1). Accumulated knowledge about hair breakage in these grooming processes indicates that hair breakage in combing and brushing results from tangling, looping, knotting, and impact loading. Fatiguing, though responsible for some weakening of the fi ber in the grooming process, it is unlikely to be a signifi cant factor in hair breakage in combing and brushing. INTRODUCTION Hair breakage is a complex multifactorial phenomenon involving: Tangle formation with hair fi bers looped over other hairs and severe bending deformations • (2) Impact breakage (3) or pulling a comb or brush through a tangle with breakage • Knots (4) that form more with high curvature and are easily fractured • Treatments and weathering (5–10): Chemical damage increases breakage and • conditioners decrease breakage Relative humidity or water content of the hair (10,11): Highly coiled hair breaks • more by dry state grooming (10) while straight-to-wavy hair provides more short segment breaks ( 2.5 cm) when dry (10), but more long segment breaks when wet (10) Physical damage or wear by abrasion (1,3,10,12) from specifi c grooming devices such • as combs, picks or brushes, and to some extent a fatiguing action

JOURNAL OF COSMETIC SCIENCE 580 DISCUSSION TANGLE FORMATION INVOLVING HAIR FIBERS LOOPED OVER OTHER HAIRS AND SEVERE BENDING DEFORMATIONS The number and complexity of tangles increase with hair fi ber curvature (10,11), produc- ing higher combing forces as shown by Epps and Wolfram (11) in the midlength and end peak regions of combing force curves. Even with relatively straight-to-wavy hair, in dry combing, tangles form near the tip ends from end wrapping, leading to a higher end peak force with a relatively low midlength force as shown by Kamath and Weigmann (13). Brown and Swift (2) examined the combing of Caucasian hair tresses in the scanning electron microscope (SEM) and observed that severe bending deformations in hair tangles are involved in hair breakage. They observed further that “the tangle tightened to the extent that a few individual hairs began to break and this occurred predominantly at a loop.” Since this type of break occurred frequently, they examined hair fi ber loops near the root end and tip end of the fi bers and noted two types of loop breakage. One type of loop involved pulling both ends of a hair fi ber so that virtually no slippage occurred. Near the root end they observed smooth fractures, but as the site of the loop moved down toward the tip they observed more longitudinal splitting or step fractures until fi brillation oc- curred near the tip end. With another type of loop, they attached one end and pulled on the other end, which resulted in the hair moving slowly as it tightened over the wire. In this case they always observed longitudinal splitting due to high stresses building at the crack tip having a strong tendency to diverge in the axial direction. Robbins (3) observed similar effects by looping hair fi bers over other hairs and fracturing by impact loading. IMPACT BREAKAGE OR PULLING A COMB OR BRUSH THROUGH A TANGLE WITH BREAKAGE Impact loading involves tangle formation and the grooming force to brush through a tangle. It has been demonstrated that hair fi bers can be broken more easily by impact with virtually no increase in length (as in tensile loading) and that hair fi bers break more readily by impact loading than by tensile extension (3). Therefore, hairs can be broken by impact (3), which involves rapidly pulling a brush or a comb through a tangle where one or more hairs are looped over another hair or by pulling through a diffi cult snag of looped hair (2). Whether or not it is necessary for the fi ber to be previously weakened by wear or by fatiguing may be determined by the type of fracture because Kamath and Weigmann (13) have described different types of hair fractures, specifying some conditions, and Robbins et al. (14) have described in more detail conditions that produce different types of hair fractures. Furthermore, some hair fi bers broken in tress combing experiments have been shown to provide smooth breaks (3) indicative of minimum prior damage (13,14) from wear or fatiguing. KNOTS FORM IN HIGH CURVATURE HAIR AND ARE EASILY FRACTURED Knot formation is also related to fi ber curvature, being highest in African-type hair (4). Khumalo et al. (4) demonstrated that more broken hairs are formed on African hair by