- Using first principles, it is demonstrated that radiative damping alone cannot lead to a nonvanishing linear electro-optic effect in a chiral isotropic medium. This conclusion is in contrast with that obtained by a calculation in which damping effects are included using the standard phenomenological model. We show that these predictions differ because the phenomenological damping equations are valid only in regions where the frequencies of the applied electromagnetic fields are nearly resonant with the atomic transitions. We also show that collisional damping can lead to a nonvanishing linear electro-optic effect, but with a strength sufficiently weak, it is unlikely to be observable under realistic laboratory conditions. 2003 The American Physical Society.