Biological factors. For biological agents affecting stored products, protective coatings applied to them and the packaging of these products belong: bacteria, molds, insects and rodents. The importance of biological factors in the corrosion process of metal products stored after their preservation is much less than the influence of humidity and air pollution. Moreover, the influence of biological factors is limited only to these areas, in which an intense biological life develops, e.g.. in areas of tropical jungle. Harmfulness of biological factors, which, as emphasized, occur mainly in tropical zones, it is of two kinds. They can emit substances that are harmful to the metal and cause its corrosion, or indirectly destroy the protective coating and packaging, thus aggressive agents, e.g.. moisture, have easy access to stored metal objects. The products of protein metabolism are among the aggressive substances secreted by bacteria and molds, e.g.. hydrogen sulfide, cysteina, ammonia, amino acids etc.. These factors accelerate the corrosion of metals.