A theory of polaritons in disordered materials is proposed with the help of Green functions and diagrammatic methods. Rayleigh scatterings in SiO2 and GeO2 glasses are calculated and the magnitudes of contributions to Rayleigh scattering from different disorder mechanisms are analysed based on the theory, which verifies the assumption in the fictive temperature approximation that Eayleigh scatterings in glasses come mainly from the density fluctuations in the glass solutions. The Rayleigh scatterings as well as the effecie of polariton dispersions on the losses are calculated for SiO2 and GeO2 glasses. The results show that at the minimum loss wavelengths, the relative deyiations of the Rayleigh scattering losses caused by ihe dis persion effects from the λ-4 law are 20% and 11% for SiO2 and GeO2 glasses respectively.