This document summarizes several naturally occurring chemicals in foods that can cause foodborne illnesses. It describes the symptoms caused by ciguatoxins from contaminated tropical fish, scombrotoxin from fish stored at improper temperatures, shellfish toxins from algae-contaminated shellfish, and mycotoxins produced by certain molds. It provides examples of foods that contain chemicals like amygdalin, ipomeamarone, furocoumarins, glycoalkaloids, lectins, trypsin, oxalic acid, cucurbitacins, cyanogenic glycosides, and goitrogens, and symptoms of ingesting these chemicals. Prevention methods focus on proper storage, cooking, and