  We analyze the effect of gravitational back reaction on cosmic string loops
with kinks, which is an important determinant of the shape, and thus the
potential observability, of string loops which may exist in the universe today.
Kinks are not rounded off, but may be straightened out. This means that back
reaction will only cause loops with kinks to develop cusps after some
potentially large fraction of their lifetimes. In some loops, symmetries
prevent even this process, so that the loop evaporates in a self-similar
fashion and the kinks are unchanged. As an example, we discuss back-reaction on
the rectangular Garfinkle-Vachaspati loop.
