A hypothesis is proposed in this study to account for the origin of sorption hysteresis. The hypothesis is based on the published research evidence that during a sorption process phase change within a material causes temperature gradients which induces heat transfer. The rate of heat transfer in turn greatly influences phase changes and mass transfer leading to the redistribution of the sorbate during a sorption process. Hysteresis is a result of the sorbate mass redistribution. It is shown thermodynamically that sorbate mass redistribution or rather hysteresis, is an inherent process in order for a material to protect itself from distortion under the extremity of local temperature alteration. Based on the proposed hypothesis, a general mathematical model is developed to quantify the hysteresis loop. The model agrees with the published hysteresis data for food materials.