Keratin fibers and the silk protein fibroin are much more susceptible to chemical than physical deterioration. At high concentrations and/or elevated temperatures, acids and alkalis break down protein amino chains of these fibrous proteins and modify selected amino acid side chains. Oxidizing agents also attack protein main chains and selected amino acid sides chains. The disulfide bonds in keratins are also susceptible to attack by oxidizing and reducing agents. Both Light below 350 nm and heat above 150° C cause the degradation of keratin by using air as an oxidizing agent. However, the mechanism of initiation of heat degradation differs from the mechanism of initiation of light degradation. The chemical processes involved in the degradation of keratins and silk by acids, alkalis, oxidizing agents including bleaches, reducing agents and by light and heat induced oxidation are briefly described in this paper.