Light induced creation and thermal annealing of metastable dangling bonds in undoped hydrogenated amorphous silicon have been investigated by electron spin resonance and photoconductivity measurements. The kinetics of the formation process can be described consistently by a self-limiting mechanism based on nonradiative tail-to-tail recombination of photoexcited carriers as the defect inducing step. The kinetic behavior of the annealing process is consistent with an exponential decay of the metastable dangling bonds with a wide distribution of thermally activated decay constants.