Evaluation method of the degree of hair damage. (I). Measurement of tensile strength of human hair by "the multi-point tension test method".

The study developed a method called 'the multi-point tension test method' to evaluate hair damage by measuring the tensile strength of human hair. By shortening the gauge length to 1 mm, the method improved accuracy in measuring the cross-sectional area and allowed for easier microscopic examination. This technique enabled the assessment of hair strength at various points from root to tip, revealing the accumulation of daily damage over time. Japanese normal hair was categorized into five strength levels. The method also demonstrated the effects of cosmetics containing collagen or keratin derivatives and identified correlations between hair strength and certain metals. Additionally, a technique for confirming the sorption of keratin peptide into hair was investigated, proving useful for studying keratin peptide characteristics.