Surprisingly, it has now been found that, when a hair care agent including at least one casein hydrolysate is applied, the hair growth itself and thus also the structure, elasticity, strength, resistance, and shine of the keratin fiber are significantly improved. Furthermore, is has surprisingly been found that the compositions according to the invention are suitable for triggering the release of growth factors and for strengthening and thickening the hair by stimulating the proliferation of the hair keratinocytes. The stimulation of the keratinocytes of the outer root sheath, which are partly responsible for the formation of the hair shaft, occurs by means of the growth factors HGF and KGF. Effects such as the “overconditioning” of the hair are avoided by means of the biologically based hair thickening. The hair grows more intensely from the root on and with a larger diameter, so this effect is particularly long-lasting.
