These Cooking Oils Have The Lowest Smoke Point
If you've ever accidentally set your smoke alarm off while cooking something in oil over high heat, you were probably using cooking oil with too low of a smoke point. Many healthy cooking oils have low smoke points, so it is important to have a healthy oil with a high smoking point on hand as well. When cooking oils reach their smoking point, they often release toxic fumes and harmful free radicals off into the air. So, understanding which oil to cook with is actually quite important for your health — and not just as a source of healthy fats (via Baseline of Health Foundation).
Unrefined oils tend to have lower smoke points, including unrefined flaxseed oil, wheat germ oil, and walnut oil. Experts suggest not heating those up at all. Unrefined safflower, sunflower, and corn oils all smoke at about 225 degrees Fahrenheit, which is very low, and should not be heated either (via The Globe and Mail).
Oils that have the highest smoke points — and are best for cooking at higher temperatures — include refined oils, such as avocado oil, almond oil, canola oil, grapeseed oil, peanut oil, and sesame oil.
Why you should avoid cooking with oils with low smoke points
Unrefined oils that have a low smoke point tend to be attractive in the first place because these oils are left in their natural state. This means that they have all of their natural nutrients and are full of flavor. While this makes low-smoke oils wonderful for drizzling over dishes or in salad dressings, these oils are more likely to oxidize when heated, and when the oil oxidizes, it lets off potentially carcinogenic compounds. Plus, unrefined oils spoil a lot faster too if not stored properly (via Very Well Fit).
It is generally safe to assume that the higher the point at which an oil smokes increases, the more refined the oil is, simply because there are fewer free fatty acids within the oil. It's these free fatty acids that cause the oil to smoke, so the more abundant they are, the more easily the oil will smoke — and they'll do so at a lower temperature.
So, stick to using unrefined oils for dressing dishes, and keep your typical cooking oils on hand for high-temperature cooking.