SUNLIGHT AND PRETREATED HAIR 87 only significant for untreated, bleached, or dyed hair. A photochemical influence of IR irradiation on the elongation properties of untreated or cosmetically treated hair is not detectable. The major part of mechanical and consequently protein chemical damage of human hair is caused by irradiation with UV-A, followed by VIS (elongation). Both irradiation ranges cleave the S-S cross-links photooxidatively (12), which results in an additional loss in tensile strength. Under the tested conditions, an additional effect on the irradiation-induced reduction of elongation brought about by cosmetic treatment could not be improved. LIPID DETERMINATION The internal lipids of hair are derived from the cell membranes of the living tissue and form ca. 50% of the cell membrane complex (CMC) between the keratinized cells of the cortex and the cuticle. Since this CMC plays a role in the diffusion properties of solubilized substances and is, furthermore, responsible for the cohesion of hair cells (13), the quantitative modifications of the CMC lipids were determined as a function of cosmetic treatment, and the type of irradiation was determined by quantitative deter- mination of the cholesterol fraction. The results are shown in Table IV. Non-irradiated, untreated hair contains ca. 1 mg cholesterol per gram of hair. This corresponds to 20-25% of the total lipid fraction (14). In contrast to permanent-wave treatment or dyeing, the chemical bleaching process reduces the cholesterol content of the untreated hair by 12% (Table IV, line 1: non/irradiated). UV-B irradiation reduces the cholesterol content of perreed or bleached hair only in- significantly (Table IV, line 2: UVB). The influence of UV-A (Table IV, line 3) is detectable from the reduction of the cholesterol content by ca. 25% in the case of untreated, permed, or bleached hair as compared to the initial concentrations. Visible light (Table IV, line 4: VIS) results in the largest photochemical degradation of cho- lesterol. Still, in untreated, perreed, or dyed hair, 42%, 60%, and 66%, respectively, of the original cholesterol content could be detected in chemically bleached and addition- ally VIS-irradiated hair, 26% of the initial cholesterol content is still detectable. This confirms the results from the most recent publications, which emphasized for the first time the photooxidative destruction of cholesterol from internal lipids in medium blonde hair by UV-A light (15) and in particular by visible light (3). Table IV Modification of the Cholesterol Content of Untreated and Cosmetically Treated Human Hair After Irradiation With Individual Parts of Sunlight for Four Weeks Amount of cholesterol in pg/g hair Untreated Permed Bleached Dyed Non-irradiated 970 908 856 948 UV-B 986 836 788 916 UV-A 748 734 548 948 VIS 416 482 208 604 IR 840 884 768 780

88 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS The influence of irradiation on permd hair does not differ from the photochemical modifications in untreated hair. Thus, an increase in the photooxidative lipid modifi- cation by the permanent-wave process cannot be detected, which is in accordance with results from. Hilterhaus-Bong (14). Irradiation of dyed hair with VIS increases the photochemical cholesterol degradation, which is already significant in natural hair, by another 40% contrary to what is seen in untreated hair, UV-A and UV-B do not result in a detectable photodegradation of cholesterol. This result can possibly be explained analogous to the dyeing processes in wool finishing. In that case a stabilization of the fiber occurs from the dyes introduced into the wool fiber, as these additionally cross-link the wool proteins. As a result, the fibers swell less, which in turn results, due to the reduced diffusion of water, in a lower photochemically initiated lipid oxidation. Irradiation of chemically bleached hair results, in comparison to untreated hair and both instances of cosmetically treated hair, in the largest modification. Visible light decreases the cholesterol content by 75%, UV-A decreases it by 42%, and UV-B decreases it by 8%. Chemical bleaching accelerates the photochemical lipid degradation, which can be put down to the lower self-protection of the hair fiber by the chemically and photooxi- datively degraded melanin. SUMMARY According to previous results (1-3), UV-A and VIS modify the morphological and chemical properties of human hair significantly, with UV-A mainly resulting in a damage of the proteins, whereas VIS mainly modifies photochemically the natural color pigments and the internal lipids. A comparison of the patterns of modification from cosmetically treated and untreated human hair after irradiation with different parts of sunlight allows statements about synergistic effects between chemical and photochemi- cal influences. As a result of the permanent-wave treatment cystine cross-links are reduced and subse- quently reoxidized using 2 % H202 for 10 min under partly prolonged treatments (Table V). Subsequent photooxidative processes on perreed hair show only an intensification regarding the degradation of melanin by VIS. The hair brightens more in comparison to untreated samples and becomes more yellow. A trend towards an increase in an irra- diation-induced degradation of proteins or lipids could, in the present investigation, only be detected with regard to loss in tensile strength. Accordingly, permed hair shows, in contrast to bleached or dyed hair, the lowest additional damage after irradiation with sunlight and does not differ significantly from Table V Concentration and Duration of Contact of Human Hair with H202 During Permanent Waving, Bleaching, and Dyeing Treatment H202 concentration (%) Reaction-time (rain) Permanent waving 2 10 Bleaching 4 40 Dyeing 3 30