If the shelf life is still a few days, it can still be eaten. If the expiration time is too long, don't eat it. Oil contains a lot of unsaturated fatty acids, and the unsaturated fatty acids in expired oil are oxidized, which is not good for health.

Edible oil, especially residual oil, contains more plant residues, which may lead to rancidity of oil. Edible oil contains linoleic acid, which easily reacts with oxygen in the air. This phenomenon is called "oil oxidation". A series of reactions such as oil hydrolysis can produce decomposition products such as aldehydes, ketones, carboxylic acids and other small molecular oxides and peroxides with special odor. The pungent smell is the result of oxidative rancidity of oil. After rancidity, the oil is heated and smoked, which contains decomposition products such as epoxypropanal, which is easy to be poisoned after eating.