The mixing of atomic levels with opposite parity in the electric field induced by the blackbody radiation is studied. These studies are applied to the case when the source of blackbody radiation is the Cosmic Microwave Background. Our interest is focused on the 2s level of hydrogen, which played an important role during the epoch of cosmological recombination. Our studies show that the broadening of the 2s level due to the mixing effect induced by the blackbody radiation leads to a correction to the properties of Cosmic Microwave Background. This correction is of the same order as the other important corrections found during the last decades and is at the level of accuracy of the modern experimental data obtained from space probes.