Rapeseed oil has some health concerns primarily because most of it is heavily processed and contains erucic acid. The processing involves chemicals like hexane, which may leave toxic residues, and high heat which causes oxidation of polyunsaturated fats. This oxidation leads to the formation of toxic by- products linked with cancer and dementia. The oil is about 30% polyunsaturated fats (omega-6 and omega-3), but during industrial processing, it is prone to degradation, creating harmful compounds. Additionally, rapeseed oil contains erucic acid, which in large amounts has been associated with adverse heart effects in animals, though human data are limited and uncertain. Most rapeseed oil in stores is also genetically modified, which raises concerns for some people about allergies and long-term effects, although current evidence generally considers GM foods safe. Overall, the heavy refining, potential oxidation, and presence of erucic acid are the main reasons rapeseed oil may be considered bad for health, especially if consumed in large amounts or used for high-heat cooking.