Hair care products evaluation

The increased tendency to change, more and more widespread in recent years has led people to change the look of their hair in an increasingly more frequent way. The effectiveness of the hair products should be demonstrated and established during research and development through scientific testing to obtain reliable performance and quality.\nGiven its structure, the hair has considerable mechanical properties. Their measure is one of the most interesting means for evaluating the integrity and the characteristics of the fibers, since very small change in chemical composition or structure of the hair can significantly alter its mechanical properties.\nFor many years, the study of stress-strain behavior (strain-stress test) is slightly used in textile industry to analyze the behavior of natural fibers.\nAlso with regard to the hair, the tensile properties have been studied . Generally, these are measured with an instrument called “extensometer” that provides a curve in response to "stress / strain", which represents the relationship between applied strength and extension of a single fiber of the hair.\nWe verified, however that the mere fact of strength and breaking does not provide useful and reliable information for the assessment. We have therefore developed a method that allowed us to analyze the behavior of the hair subjected to treatments of coloring and/or bleaching more or less aggressive.\nThe obtained results are in agreement with those obtained through "test in use". The method is therefore a valuable tool for the evaluation of hair products “in vitro” allowing a wide screening.