When you heat different cooking oils really hot for a long time, they break down and make harmful chemicals, and the type of oil you use determines which chemicals are made.

The kind of fat in an oil—like how much linolenic, linoleic, or oleic acid it has—decides what chemicals are made when you heat it up, and how much of them.

Two harmful chemicals — HHE and ethyl furan — show up together when you heat oils like perilla oil, and they both come from the same type of fat: linolenic acid.

Oils with polyunsaturated fatty acid content exceeding 10% are susceptible to thermal oxidation during cooking, generating harmful aldehydes and polar compounds even below smoke point.

Oils with polyunsaturated fatty acid content exceeding 10% are susceptible to thermal oxidation during cooking, generating cytotoxic aldehydes and lipid peroxides.

When you heat olive oil at high temperatures for a long time, it makes more of two harmful chemicals—HNE and ONE—than the other oils, because olive oil is mostly made of oleic acid.