Oils with more unsaturated fats (like sunflower and sesame) break down faster and make more harmful chemicals when heated or left in the sun than oils with more saturated fats (like peanut or olive).

Leaving cooking oils in the sun for a long time makes them break down and form harmful chemicals, especially if they’re made from seeds with lots of unsaturated fats.

Whether you leave oil in the sun or fry food in it, the same bad chemicals form — just at different speeds.

When you fry food over and over again, some cooking oils break down faster than others—oils with more saturated fats (like coconut or palm oil) hold up better and make fewer harmful gunk particles than oils with lots of unsaturated fats (like sunflower or olive oil).

When you reuse cooking oil over and over again, it starts to break down and create bad-smelling chemicals that can make food taste funny and might be bad for your health.

Oils like peanut oil don’t break down as quickly when you fry food compared to butter or vegetable oils, making them a bit more stable at high heat.