Gutter oil is an expression used for the gutter oil extracted from drains or sewage systems. this gutter oil is widely used as a cheaper alternative for refined cooking oils by small street food vendors. the uv-visible spectroscopy technique is adopted in this study. the spectra were repeatedly recorded before and after boiling the oils in a period of 3 hours. the results revealed that re-heating the oils several times changed their chemical structures as well as their physical and chemical properties. in frying, cooking oil is heated to a temperature of 170-220 degrees celsius. upon heating, cooking oil may undergo chemical reactions, hydrolysis, oxidation and polymerization. besides, the viscosity of the cooking oil will increase; its color will become darker and rancidity will also develop, giving rise to unpleasant flavor. the frying process relies on high temperatures and can change the structure of labile nutrients, such as protein, vitamins, and antioxidants as they strongly interacts with lipids, especially with thermal and oxidative degradation products generating toxygenic and carcinogenic compounds. some water-soluble molecules, such as ascorbic acid and can be lost during the water evaporation. during frying, oil degrades mainly via thermal oxidation and form volatile (vdp) and nonvolatile decomposition products (nvdp). when food is immersed in hot oil in the presence of o2, the oil is exposed to three agents that cause changes in its composition: water from the food, oxygen and finally, the high temperatures. water, a weak electrophile, attacks the ester linkage of triacylglycerols and produces di- and mono-acylglycerols, glycerol, and free fatty acids. glycerol evaporates at 150 degrees. and the remaining glycerol in oil promotes the production of free fatty acids by hydrolysis. several intermediate products called amadori products or pre-melanoidins are rapidly polymerized at frying temperatures, forming dark colored molecules. in one recent study, increasing of treatment time and temperature in potato chip, acrylamide contents were increased. acrylamide is a toxic compound produced by maillard reaction. it is neurotoxic, genotoxic and carcinogenic. uv-visible spectroscopy has been used. uv-visible spectra were collected using labtronics uv-vis spectrophotometer model lt-2800 and a 1-cm path quartz cuvette. a dual beam uv-visible spectrophotometer was used to study the transmission characteristics of these refined oils. commercially available samples of the oils were used in this study and a good quality oil was chosen as a standard. in second study, a boneless chicken piece was fries in oil at 300°c for 3 hours. in the third study, each oil were used to fry potato chips for 3-hours with collection of sample at every half an hour interval in every study. uv spectra of all the samples was taken and a comparative graph was drawn. the uv spectra of the thermally treated oils changed dramatically when compared with the raw oils. this reflects a change in the chemical structures of the oils. the presence of toxicity like various metal ions, dyes, aldehyde and carboxylic functionality was analyzed chemically. we have been able to detect the presence of dyes in the oil samples. these dyes can have a toll on our health if consumed. we thus concluded from the research that several factors can affect the quality of cooking oil during heating, including ventilation, temperature, heating duration, the type of oil, the saturation ratio of the oil, and the presence of a catalyst/antioxidant. the repeated heating of oil at high temperatures (≥180°c) results in the thermal oxidation of the oil, which causes the configuration of the fatty acid to change from the cis isomer to the trans isomer. this configuration change causes the pufas to acquire undesirable properties associated with sfas, such as their correlation with increased serum cholesterol levels and higher low-density lipoprotein (ldl) cholesterol in particular. social relevance recently much concern has been expressed on the biological effects of oxidized lipids, and there is increasing evidence that they may be detrimental to health. so our project aims in finding out the toxic effects of gutter oil and making people aware about this too. the free radicals produced during repeated heating process reacts with parts of cells, such as molecules of dna and protein and may become attached to those molecules, causing abnormalities of structure and function. if used oil is not properly strained and stored after it cools, bacteria feeds on food particles left in the oil. rancid -- meaning old and stale -- oil contains free radicals, molecules that can damage cells and lead to increased cancer risk, as well as affect the quality of your food. the purpose of this study is to see the risk of food poisoning associated with gutter oil in order to determine the magnitude of the problem, risk factors, monitoring and surveillance, and measures of control.