Damage assessment of human hair by electrophoretical analysis of hair proteins

The assessment of the damage induced by cosmetic processes on human hair is very important for the cosmetic industry, constituting the first step to prevent hair deterioration and to develop new products. The electrophoretical fractionation (SDS-PAGE) of hair proteins leads to a specific electrophoretical pattern, whose regions can be attributed to the morphological hair components. In the present study, assessing the status of human hair and its changes imparted by cosmetic processes is realised through gel-electrophoretical fractionation of hair proteins. The basis of the study is represented by the fact that all cosmetic processes influence the morphological components of the hair fibre and their proteins and that the modifications of the proteins are specific, a characteristic type and degree of damage being induced by each cosmetic treatment. Under standardised conditions the soluble proteins are extracted as S-carbamidomethylated derivatives, subjected to sodium dodecyl sulphate polyacrylamide gel electrophoresis and the resulting gels are stained with Coomassie Brilliant Blue R 250. The densitograms obtained by densitometric measurements of the stained gels are digitised and subjected to cluster analysis, a method of multivariate statistics able o identify the similarities between the digitised protein profiles. The cosmetic treatments are applied on a commercial, European mixed hair sample. Besides oxidative and reductive treatments, carried out as single and multiple treatments, at different treatment duration, styling procedures such as hot curling are performed. The influence of the contact with swimming pool and sea water is also investigated. Cumulative effects of cosmetic processes on hair proteins are studied applying combined cosmetic treatments. The results obtained using the analysis of the electrophoretical patterns for cosmetically treated samples are compared, for selected cases, with the results of traditional methods for assessing hair damage such as amino acid analysis, tensile strength measurements and differential scanning calorimetry. Cluster analysis performed separately for the keratin intermediate filament proteins and for the keratin-associated proteins allows the identification of the morphological components affected by a certain cosmetic treatment and the comparative evaluation of the induced damage degrees. A database of characteristic changes of the electrophoretical protein pattern is built by the analysis of hair samples subjected to standard cosmetic treatments, in conformity with the usage instructions. This database is subsequently used for evaluating the effects of any other non-standard cosmetic treatment on the morphological components of the hair fibre. UV-irradiation and cosmetic processes have cumulative influence on hair proteins. The enlargement of the application area for the developed method is suggested by the efficacy evaluation of a series of hair sunscreens applied on hair samples subjected to UV-irradiation