Product Untreated hair Untreated hair Ammonium hydroxide Ammonium hydroxide Ethanolamine Ethanolamine Post- treatment None Dialysed None Dialysed None Dialysed Table II The Effect of Alkalizers on HPDSC and Tensile Strength Plateau load Gmf/sq.micron (x 103) 5.73 ± 0.35 5.17 ± 0.40 5.15 ± 0.38 Tensile strength measurements Load@ 25% Gmf/sq.micron (x 103) 6.81 ± 0.52 6.06 ± 0.39 5.96 ± 0.38 Break load Gmf/sq.micron (x 103) 20.59 ± 1.6 18.86 ± 3.1 18.91 ± 2.6 Peak temp T0±s (°C) 149.0±0.1 147.9 ± 0.2 142.8 ± 0.5 150.7 ± 0.4 147.5 ± 0.1 150.1±0.1 Enthalpy LlH0±s CT/g) 11.0 ± 0.4 8.6 ± 0.9 9.1±0.8 10.1±0.1 8.3 ± 0.2 9.1 ± 0.3 N 0 0 0\ ,.., � � ("') tn ,.., 0 z ("') 0 z tn � tn z ("') tn VJ N VJ

324 Ammonium hydroxide soak pH JOURNAL OF COSMETIC SCIENCE Table III The pH Measurements During Dialysis DI water control 1 1 2 1 3 1 6.67 9.10 8.30 7.33 41 5 1 61 6.74 6.68 6.69 temperature and enthalpy. As the alkalizer can removed on dialysis, or by multiple washing cycles, the effect of these alkalizer components is not linked to permanent oxidative cleavage of the covalent bonds (e.g. cystine) but to temporary effects that are reversible and not damaging to the fiber. Extending this hypothesis to full formulations of hair colorants and bleaches, we may expect to see the combination of the two effects on the denaturation peak temperature and enthalpy: a change due to the irreversible oxidation of the covalent bonds, and a reversible effect due to the incorporation of components such as salts, alkalizers and formulation ingredients. To test this hypothesis the untreated hair was treated with five repeat cycles of product C. After cycles 1, 3 and 5 two swatches were removed and dialysed. In addition the tensile strength properties of the hair were measured at the 1, 3 and 5 cycles. The results are summarised in Table IV. The data in Table IV show that for one cycle of treatment the effect of the product, as measured by T d is reversible. Three cycles of treatment shows incomplete recovery of the peak temperature. At cycle 5, the peak temperature remains depressed indicating per- manent damage to the fibre. This result correlates with both visual observations of the hair tresses and the measured tensile strength properties. The tensile properties signifi- cantly decrease on repeat treatment and observationally the hair breaks easily on comb- ing and brushing. The reversible effects observed in the tables above are likely to represent a change in the environment of the intermediate filaments rather than a change in either the crystallinity or amount of crystalline material in the IFs. It is predicted that other product compo- nents can display this reversible effect on the HPDSC data, and specifically product components that can readily penetrate into the fiber and interact with the IFAPs via electrostatic interactions. Such product components include salts such as sodium, po- tassium, ammonium carbonate or persulfate salts and surfactants such as alkyl and alkoxy sulfates and sulfonates. In addition, we may expect to see some changes due to the increased uptake of calcium and magnesium ions as the hair is treated with multiple cycles of bleach treatments. Figure 1 sets out conceptually a proposed mechanism of these reversible and irreversible effects. The findings in this study demonstrate the need for careful interpretation of HPDSC data in the context of formulations that are designed to change morphological compo- nents within the hair cortex e.g. bleaches, perms, colors etc. Where the site of product action is known to be the cortex (intermediate filaments, matrix, pigment) one should also expect some ingredients to remain in the fibre pending removal by repeated wash- ing, as is the practice by consumers. In this case it is essential to separate permanent and temporary changes to the cortex when employing HPDSC methods.