SUNLIGHT AND PRETREATED HAIR 89 irradiated natural hair in the extent of photochemical modifications of proteins and lipids. Bleaching is achieved by 40-min exposure to 4% H202 (Table V), which oxidatively destroys the color pigment, melanin. As a result, hair on the whole becomes brighter. This desired effect is supported especially by irradiation with visible light and by UV-A, so that these hairs fade to a much larger extent than natural hair. However, these hairs not only become brighter, but also more yellow and more green. The protein and lipid components of human hair are already significantly damaged by the chemical bleaching process. Irradiation with UV-A and VIS leads to a further modification of both com- ponents so that considerable losses in tensile strength and decreases in the lipid content have to be accepted. In accordance with the degradation of lipids in irradiated wool, this can mean reduction in cell cohesion and plasticity of the total fiber (18). Furthermore, a loss in lipids promotes the diffusion of foreign substances along the damaged CMC into the hair fiber and thus supports further modifications of the hair (17). Human hair is sensibilized towards photochemical modifications of all three chemical components following chemical bleaching. Melanin pigments (partly desired) and pro- teins and lipids (both undesirable) are particularly modified to a large extent by UV-A and visible light. Therefore, in this case a synergistic fiber damage as a result of bleaching in combination with irradiation with sunlight could be demonstrated. Dyed hair is exposed to lower concentrations of, and shorter treatment times with, H202 than is the case for bleached hair (30 min 3% H202, C/f Table V). In addition, it is treated with a red pigment. These hairs become orange-yellow, especially after irradia- tion with the visible part of sunlight. It is therefore assumed that the red pigment acts in addition to the natural brown pigment in the VIS range as a photoreceptor and that it is also photochemically degraded. A protein chemical modification due to irradiation with VIS occurs to a lower extent than that observed for cosmetically untreated hairs. Furthermore, photooxidative degradation of IL both in the UV-A and the VIS range is lower. It is therefore assumed that during oxidative dyeing the color pigments attach to hair proteins in a fashion similar to that in wool dyeing, impede conformational changes, and thus stabilize the proteins because of additional cross-links (16). Therefore, H202 molecules can only diffuse to a lower extent into the hair, and consecutive photochemical reactions of the proteins and lipids are reduced (19). Thus, the present results indicate that hair can be protected by oxidative dyeing from photochemical degradation reac- tions, but that it is in turn subject to undesirable color changes. MECHANISM OF PHOTODEGRADATION In the following, several reaction mechanisms are presented that can lead to a synergistic effect between cosmetic pretreatments and irradiation of human hair. 1. Bleaching and permanent waving result in an increase in the water retention value as hairs show stronger swelling (20). In these cases photochemical reactions can convert water to a larger extent into highly reactive hydroxy radicals that in turn destroy in consecutive reactions the chemical components of hair (increased loss of tensile strength and lipid degradation in bleached hair). Conversely, examination of dyed hair indicates a reduced photochemical destruction because dyeing makes swelling more difficult (reduced loss in tensile strength).

90 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 2. The photochemical reactions of cosmetically modified hairs are intensified by chemicMs remai,ing in the hair. In particular, H202 is taken into consideration, as (a) all examined cosmetically treated hairs had come in contact with H202 (c/f Table V), and (b) H202 can be transformed under irradiation into highly reactive hydroxy radicals (photochemi- cal melanin degradation correlates with duration and concentration of 8202 treatment). 3. Mela,i, is assigned a key role in the photochemical reactions. The extent of photo- chemical damage in many investigations deals with the cortex directly, dependent on pigmentation (1-4). In the present investigation, dependencies could, however, only be demonstrated between the duration of irradiation and degradation of melanin on the one hand and H202 treatment and pigment destruction on the other. Bleached hair is photochemically brightened the most, followed by dyed and permed samples. CONCLUSIONS On the basis of significant fading and yellowing of cosmetically treated hairs, protection against sunlight-induced (U¾-A and ¾IS) color changes is recommended for permed and dyed hair. Chemically bleached hair needs an additional protection against photochemi- cally caused protein and lipid modifications (U¾-B, U¾-A, and ¾IS), as these damage the structure of human hair. REFERENCES (1) E. Hoting, M. Zimmermann, and S. Hilterhaus-Bong, Photochemical alterations in human hair. Part I: Artificial irradiation and investigations of the hair proteins,J. Soc Cosmet. Chem., 46, 85-99 (1995). (2) E. Hoting, M. Zimmermann, and H. H6cker, Photochemical alterations in human hair. Part II: Analysis of melanin, J. Soc Cosmet. Chem., 46, 181-190 (1995). (3) E. Hoting and M. Zimmermann, Photochemical alterations in human hair. Part III: Investigations of the internal lipids, J. Soc Cosmet. Chem., 46, 85-99 (1995). (4) M. Tatsuda, M. Uemura, K. Torii, and M. Matsuoka, Studies on hair damage and demelanization by ultra violet light,J. Soc. Cosmet. Chem. Japan., 21, 43•49 (1987). (5) G. Reese and N. Maak, Die Bestiindigkeit yon Haarfarben unter dem EinfiuB yon Sonne, Wasser, Salz, •rztL KosmetoL, 12, 373-379 (1982). (6) G.J. Smith and W. H. Melhuish, Fluorescence and phosphorescence of wool keratin excited by UV-A radiation, Text. Res. J., 55,304-307 (1985). (7) K. R6per and E. Finnimore, Chemical structure of chromophores formed during photoyellowing of wool, Int. Wool Text. Res. Conf. Tokyo, IV, 21-31 (1985). (8) A. Elliott, The o•-[3 transformation in streched hair, Text. Res. J., 22, 783-786 (1952). (9) C. R. Robbins and C. Kelly, Amino acid composition of human hair, Text. Res. J., 40, 891-896 (1970). (10) P. Alexander, A. Fox, and R. F. Hudson, The reaction of oxidizing agents with wool, Biochem. J., 49, 129-138 (1951). (11) C. R. Robbins, Chemical and Physical Behaviour of Human Hair (New York, 1979), pp. 161-190. (12) U. Schumacher-Hamedar, J. F•Shles, and H. Zahn, Intermediate steps in the oxidation ofcystine in the bleaching process, Textilveredlung, 21, 121-125 (1986). (13) H. Zahn, Wool is not keratin only (Plenum Lect.), 6th Int. Wool Text. Res. Conf, Pretoria, I, (1980). (14) S. Hilterhaus-Bong and H. Zahn, Contribution to the chemistry of human hair: II. Lipid chemical aspects of permanently waved hair, Int. J. Cosmet. Sci., 11, 167-174 (1989). (15) M. Zimmermann and H. H&ker, Identification and quantification of simulated sunlight induced cholesterol oxides in wool by means of GC and GC-MS, Text. Res. J. (in press).