It is known that polysorbates are prone to degradation by autoxidation. This article provides an example of a free radical chain reaction that leads to polysorbate degradation. It starts with the oxidation of fatty acid esters, either by metal-, temperature- or light-induced processes to form various fatty acid free radicals. These free radicals are usually carbon centered and react rapidly with oxygen to form alkylperoxyl radicals. Alkylperoxyl radicals promote further free radical formation by abstracting hydrogen atoms from other fatty acid ester molecules. The alkylperoxyl radicals are converted to hydroperoxides that either undergo thermolysis or react with metals to form alkoxyl, alkylperoxyl and carbon centered free radicals. This free radical chain reaction proceeds until it is terminated.