  Proton decay is a generic prediction of GUT models and is therefore an
important channel to detect the existence of unification or to set limits on
GUT models. Current bounds on the proton lifetime are around 10^33 years, which
sets stringent limits on the GUT scale. These limits are obtained under
`reasonable' assumptions about the size of the hadronic matrix elements. In
this paper we present a non-perturbative calculation of the hadronic matrix
elements within the chiral bag model of the proton. We argue that there is an
exponential suppression of the matrix elements, due to non-perturbative QCD,
that stifles proton decay by orders of magnitude -- potentially O(10^-10). This
suppression is present for small quark masses and is due to the chiral symmetry
breaking of QCD. Such a suppression has clear implications for GUT models and
could resuscitate several scenarios.
