Because neither polyethylene nor polypropylene is biodegradable, the deterioration of these fibers under laboratory conditions was investigated. Fourier transform infrared (FTIR) photoacoustic spectroscopy was used to examine the thermal and photooxidation of a melt-blown nonwoven polypropylene fabric. The photoacoustic spectra were reproduced for the two test conditions. The by-products of both thermal and photooxidation were alcohol, peroxide, aldehyde, ketone, carboxylic acid, ester, and anhydride. Thermal oxidation was inhibited by the addition of a phenolic antioxidant. The heat penetrated the bulk of the tested fabric, and thermal oxidation by-products were found throughout the sample. Photooxidation by-products were found mainly in the surfaces directly exposed to the ultraviolet light.