  In several classes of modified gravity theories, extra degrees of freedom are
not completely screened in the interiors of stellar and substellar objects. In
such theories, the hydrostatic equilibrium condition inside these objects is
altered. Moreover, the interior structures of these objects might have a small
pressure anisotropy induced by several physical phenomena, including rotation
and magnetic fields. All these effects, both individually and collectively,
induce changes in predicted stellar observables. Such changes have an impact on
different phases of the stellar life cycle, starting from its birth to its
death, covering almost all the branches of the Hertzsprung-Russell diagram. The
aim of this work is to systematically review the current literature on the
topic. We discuss the main results and constraints obtained on a class of
modified gravity theories.
