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.

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.

Cooking olive oil at a very high temperature for an hour almost completely destroys the fresh, grassy smell that makes good olive oil taste good.

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 really hot (200°C), it loses all its protective antioxidants and turns into more gunk than when heated at a lower temperature (170°C).