At the EHU-UPV (University of the Basque Country) Pharmacy Faculty they have been studying the process of the oxidative degradation of foodstuffs. Research was began with oils, given that these are exclusively (99 %) made up of lipids while, in subsequent stages, the study will be extended to other foods prone to undergoing processes of oxidative degradation. Processes of oxidative degradation Researchers investigated processes of oxidative degradation - notably that caused at 70ºC with ventilation - of a broad group of oils with very wide-ranging compositions. Another degradation process studied was that which is caused by microwave action that does not heat greater than a temperature of 190 ºC., ,In both processes deterioration of the oils takes place. In the first type of process (70 ºC with ventilation) hydroperoxides are first produced and subsequently aldehydes. In the second kind of process (microwave) it is basically aldehydes produced. It has to be pointed out that both the oxidative conditions and the composition of the oil determined the velocity of the degradation and both the nature and concentration of the compounds produced. These studies have shown, for the first time, that degradation of lipids in foods can produce toxic oxygenated aldehydes. These compounds, well-known in medical studies for their geno- and cytotoxic activity, considered as markers of oxidative stress in cells as well as being causal agents of degenerative illnesses, had not previously been detected in foodstuffs. Researchers have shown that some oils produce these toxic substances in greater quantities and at a greater rate. Virgin olive oil was, amongst all the oils studied, that which took longer to produce this type of compounds and produced a lower concentration of them. The technique Researchers carried out this investigation, studying the liquid phase of the oil by means of Proton Nuclear Magnetic Resonance and Fourier Transform Infrarred Spectroscopy, and the gaseous phase of the oil with Solid Phase Microextraccion techniques followed by Gas Chromatography-Mass Spectrometry. The confirmation of the identity of the aldehydes detected was carried out with pattern substances and with proton nuclear magnetic resonance spectra for a number of toxic aldehydes provided by American researchers who are studying the presence of these compounds in damaged cells and tissues. The presence of toxic oxygenated aldehydes in fats and oils subjected to thermal treatment highlights the need to control the manufacture and preparation processes of foodstuffs as well as the fatty material employed, given their capacity to generate these oxygenated aldehydes responsible for degenerative illnesses. This research opens new lines of investigation and perspectives in the field of food safety.