HAIR BREAKAGE: REPEATED GROOMING EXPERIMENTS 445 (IV) PRODUCT USAGE FACTORS The purpose of performing these experiments is generally to demonstrate the ability of lubricating conditioner treatments to reduce breakage. Therefore, the effectiveness of such products relates to their ability to provide dry-state lubrication. While different products will vary in their deposition effi ciency, their effectiveness is also related to the manner in which a product is used. For example, changes in the product:hair dosage ratio, the residence time of the product on the hair, and/or the rigor with which rinsing is performed will all infl uence the deposition of condition- ing ingredients. METHODOLOGY Hair tresses were treated according to our standard procedure, then allowed to air dry and equilibrate under controlled humidity conditions. In all experiments this involved apply- ing a leading commercially available conditioner product at a 15% v/w dosage, followed by massaging through the hair for one minute and rinsing for 30 seconds with 38°C wa- ter at a fl ow rate of 1 gallon/minute. Chemical damage was induced by bleaching tresses with a 6% hydrogen peroxide solution (pH 10) for 40 minutes. Unconditioned tresses, particularly those that had been chemically damaged, required carefully detangling with a wide-toothed comb prior to testing. Four tresses can be mounted on our device at the same time. The tresses are then automatically groomed in 1,000-stroke blocks, with subsequent counting of broken fi bers in the collection trays under each tress. These values are recorded, the trays are cleaned, and the tresses are cycled through another 1,000 strokes. This process is repeated until a total of 10,000 grooming strokes have been carried out. RESULTS Table I shows typical data obtained from this protocol for virgin Caucasian tresses brushed at 60% relative humidity. The most simple, and often a perfectly adequate, means of analysis involves comparing means for different treatments after a given number of grooming strokes. Figure 4 shows box and whisker plots representing breakage data for unconditioned virgin hair tresses and hair treated with a commercially available shampoo and conditioner regimen after 10,000 brushing strokes. Results convincingly illustrate the benefi t provided by such products, in that the extent of breakage in this particular instance has been reduced by approximately 60%. However, additional information can be obtained upon analyzing results in accordance with the fatigue testing principles described earlier. GROUPED WEIBULL ANALYSIS Table II illustrates how this data is treated by the grouped Weibull approach. Column 2 contains the total number of broken fi bers for all eight tresses as a function of the

JOURNAL OF COSMETIC SCIENCE 446 number of combing cycles. Column 3 then shows a running total of the number of bro- ken fi bers, or, in other words, the cumulative breakage frequency. Column 4 shows the previously described median rank approach for estimating the cumulative distribution function. On average, we have found each tress to contain approximately 2,500 fi bers therefore, the total number of fi bers across the whole experiment (i.e., N in the median rank equation) is 20,000. Columns 5 and 6 show the creation of the double log expres- sion that forms the y axis in the Weibull plot. Meanwhile, column 7 represents the x axis. It is especially convenient to set up these calculations (together with the later cre- ation of the survival probability plot) using an Excel spreadsheet. The resulting Weibull plot, together with the resulting values for the characteristic lifetime and the shape factor, is shown in Figure 5. Figure 4. Mean values for the number of broken fi bers after brushing hair tresses 10,000 times. Table I Number of Broken Fibers Generated during Repeated Brushing Experiments on Virgin Caucasian Hair at 60% RH No. of brush strokes Tress 1 Tress 2 Tress 3 Tress 4 Tress 5 Tress 6 Tress 7 Tress 8 Total 1,000 17 9 11 5 14 19 17 18 110 2,000 5 5 5 2 5 4 4 8 38 3,000 4 2 3 1 3 4 5 4 26 4,000 2 2 0 6 3 2 3 1 19 5,000 4 4 2 5 2 4 3 4 28 6,000 2 1 4 2 4 4 6 2 25 7,000 3 2 2 4 5 3 3 3 25 8,000 2 3 1 3 2 2 3 0 16 9,000 3 3 0 4 2 5 2 5 24 10,000 1 2 4 1 3 3 0 1 15 Total 41 33 32 33 43 50 46 46 326