Subject of study. Variations in the reflection coefficients of mid-infrared radiation from the surfaces of silicate, borosilicate, and lead-borate optical glasses after their contact with a humid atmosphere were investigated. Aim of study. The study was aimed at analyzing and interpreting infrared spectra of optical glasses after their prolonged exposure to a humid atmosphere. Method. Glasses with a surface polish quality of grade II were stored in hermetically sealed containers at a temperature of 23◦C and relative atmospheric humidity of 25% and 65% for 20 to 42 days and then stored in an atmosphere with a humidity of 95% at a temperature of 50◦C. A part of the samples was processed in a hexamethyldisilazane vapor to form a hydrophobic coating. Infrared spectra of the samples were recorded in the wavenumber range of 400−4000 cm−1 using a Nicolet iS10 Fourier spectrometer. Main results. The changes in the reflection coefficients are attributed to variation in the chemical composition of the surface layer of the optical glasses after their interaction with a humid atmosphere. Practical significance. The obtained results can be applied for the development of technology to increase the chemical resistances of optical glasses in a humid atmosphere. © 2022 Optica Publishing Group.