When you heat olive oil, it makes more of two harmful chemicals — HNE and ONE — than the other oils tested, likely because it’s high in oleic acid.

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.

Olive oil, which has lots of oleic acid, makes more of certain toxic aldehydes like 4-HNE and 2-decenal when heated than oils like soybean or palm.

Olive oil from Al-Jouf stays fresher longer than olive oil from Pakistan when left out at room temperature, based on how quickly it breaks down.

When you cook olive oil too hot, it starts producing chemicals that smell rancid — like old nuts or grease — and these chemicals can be used to tell if the oil has been overheated.

When olive oil gets really hot, one of its healthy compounds — hydroxytyrosol acetate — goes up, which might be a clue that the oil has been overheated.