  Regular black holes represent a conservative model in which the classical
singularity is replaced by a non-singular core without necessarily modifying
the spacetime outside the trapping horizon. Given the possible lack of
phenomenological signatures, it is crucial to study the consistency of the
model. In this short work, we review the physical mechanism leading to the
instability of the central core, arguing that non-perturbative backreaction is
non-negligible and must be taken into account to provide a meaningful
description of physical black holes.
