SHOCKING! THESE COOKING OILS TURN TOXIC WHEN HEATED When it comes to cooking, not all oils are created equal. Some oils, when heated to high temperatures, can turn toxic, causing inflammation, free radicals, and even heart issues. Here's a look at some of the most common oils you might use in your kitchen and why you should be cautious when cooking with them. Corn Oil – High in omega-6 fats, corn oil can easily oxidize at high temperatures, increasing inflammation in the body. Soybean Oil – Comm