We study the dead-core rates for the initial boundary value problem of various parabolic equations with strong absorption. Unlike in many other related problems of singularity formation, we show that the temporal rate of formation of the dead-core is not self-similar for both heat and fast diffusion equations. The proofs rely on self-similar variables and require a delicate use of the Zelenyak method. Moreover, we give some initial data so that the dead-core rate is self-similar for the case of slow diffusion. Some open problems shall also be given.
