Abstract: People usually pay close attention to the fragility of their hairs. Therefore some kinds of shampoo with the function of so-called “strengthening hair” come into being on the market. However the real effect is not clear. In this paper, the mechanical properties of human hairs, treated with a typical shampoo with the function of “strengthening hair”, are determined using tensile experiments. The results indicate that after being treated with shampoo, the yield stress of the hair decreases, which means that the ability to resist plastic deformation is weakened. Also, the ultimate stress and the ultimate strain are decreased, which means a reduced ability of the hair to resist the accidental breakage. In addition, Young's modulus goes down, showing a poor ability of the hair to resist the elastic deformation. To sum up, the shampoo studied in this paper is not helpful to “strengthen” or “toughen” hairs.