Straightening of keratinous fibers comprises application of a straightening composition containing an alpha-hydroxy acid derivative (I) and/or alpha keto acid derivative (II), having a pH of =9 on keratinous fibers and raising the temperature of keratinous fibers to 110-250[deg]C, using a heating unit. An independent claim is included for a kit comprising a heating unit having a heating range of 110-250[deg]C and the straightening composition.
