Starting from a microscopic description of a system of strongly interacting electrons in a strong magnetic field in a finite geometry, we construct the boundary low energy effective theory for a fractional quantum Hall droplet taking into account the effects of a smooth edge. The effective theory obtained is the standard chiral boson theory (chiral Luttinger theory) with an additional self-interacting term which is induced by the boundary. As an example of the consequences of this model, we show that such modification leads to a nonuniversal reduction in the tunneling exponent which is independent of the filling fraction. This is in qualitative agreement with experiments, which systematically found exponents smaller than those predicted by the ordinary chiral Luttinger liquid theory.Facultad de Ciencias Exactas