Can expired oil be used for frying food?

Generally, expired oil is not recommended for frying food. Even if it appears normal, it may still pose health risks. If in doubt, it's safer to discard it directly. Detailed analysis is as follows:

Expired oil can generate harmful substances due to oxidation and rancidity, such as peroxides and aldehydes. These compounds have poor heat resistance and will rapidly decompose during frying, producing even more toxic byproducts. These substances not only degrade the nutritional value of food but may also irritate the gastrointestinal tract, and long-term consumption could increase health risks.

Even if expired oil looks clear and has no unusual odor, it does not necessarily mean it is safe. Early stages of oil rancidity are difficult to detect with the naked eye, yet harmful substances may already be accumulating internally. When used for frying, these toxins can adhere to the surface of food, potentially causing gastrointestinal discomfort such as nausea, diarrhea, and abdominal pain after consumption. In severe cases, liver function may also be affected.

Cooking oil should be consumed within its shelf life. Store it sealed in a cool, dry place away from direct sunlight. Regardless of appearance, expired oil should never be used for cooking. If accidentally consumed and any adverse symptoms occur, seek medical attention promptly.