  General relativity allows a variety of future singularities to occur in the
evolution of the universe. At these future singularities, the universe will end
in a singular state after a finite proper time and geometrical invariants of
the space time will diverge. One question that naturally arises with respect to
these cosmological scenarios is the following: can quantum effects lead to the
avoidance of these future singularities? We analyze this problem considering
massless and conformally coupled scalar fields in an isotropic and homogeneous
background leading to future singularities. It is shown that near strong, big
rip-type singularities, with violation of the energy conditions, the quantum
effects are very important, while near some milder classes of singularity like
the sudden singularity, which preserve the energy conditions, quantum effects
are irrelevant.
