DSC measurements carried out at different heating rates were used for the kinetic analysis of the endothermic process assigned to the denaturation of the helical material from human hair in water excess. We found that the kinetic mechanism is autocatalytic and that the value of the activation energy is close to disulphide bond scission rather than to protein denaturation. This allowed us to propose a multistep mechanism for the thermal denaturation of hard alpha-keratins in water excess that relies on the 3-phase model which describes their structure. The limiting step of the thermal denaturation process is then the scission of S-S bonds between the main morphological components, namely IF and matrix (IFAP). The theoretical proposed model shows a good agreement with the experimental recorded data.