Reusing cooking oil in food preparation, especially during deep-frying, is a common practice to save costs. Repeated heating of the oil accelerates oxidative degradation of lipids, forming hazardous reactive oxygen species and depleting the natural antioxidant contents of the cooking oil. Long-term ingestion of foods prepared using reheated oil could severely compromise one’s antioxidant defense network, leading to pathologies such as hypertension, diabetes and vascular inflammation. The detrimental effects of reheated oil consumption extend beyond mere oxidative assault to cellular antioxidant shield. In this review, we have examined the experimental and clinical effects related to the intake of reheated oil on antioxidant contents, membrane lipid peroxidation and endothelial function. Understanding the mechanisms underlying the pathology associated with intake of repeatedly heated oil will help to set a reference for assessing the safety of cooking oil. Finally, considering the potential hazard of repeatedly heating oil, this article aims to further increase awareness of the general public regarding the health risks associated with these oils.