  Nuclear reactions proceed differently in stellar plasmas than in the
laboratory due to the thermal effects in the plasma. On one hand, a target
nucleus is bombarded by projectiles distributed in energy with a distribution
defined by the plasma temperature. The most relevant energies are low by
nuclear physics standards and thus require an improved description of
low-energy properties, such as optical potentials, required for the calculation
of reaction cross sections. Recent studies of low-energy cross sections suggest
the necessity of a modification of the proton optical potential. On the other
hand, target nuclei are in thermal equilibrium with the plasma and this
modifies their reaction cross sections. It is generally expected that this
modification is larger for endothermic reactions. We show that there are many
exceptions to this rule.
