The JKR method measures the adhesion between two spheres or a sphere and a plane surface, all materials being elastomers. We have used this technique to study the self-adhesion of a siloxane elastomer. Our results demonstrate that there is a large difference of behavior (hysteresis) between the loading and unloading regimes when the soluble fraction of the networks has been extracted. The unloading regime is then not described by the classical application of the JKR model. We believe that the work of adhesion measured during the unloading regime is not constant along the contact area but rather decreases from its center toward its edges. This behavior may be the signature of the JKR pressure profile (compressive in the center of the contact area and tensile near its edges) the sign and magnitude of which influence the formation of hydrogen bonds across the interface. A generalization of the JKR model that includes this feature is proposed and gives a good description of the experimental data.