The smoke point of an oil is the temperature where the chemical bonds of the fatty acids in the oil start to decompose. Heating an oil beyond its smoke point temperature will cause the oil to smoke and produce unpleasant odors. Even worse, any food cooked in the overheated oil will taste burnt. If the oil is heated too far beyond the smoke point it will reach its flash point, the temperature where the oil can catch fire. To avoid any of these problems, be sure to use a cooking oil that has a higher smoke point than the temperature you will be using to cook your food. If you only have the budget or room for one type of oil in your kitchen it’s best to buy one that has a high smoke point so it can be used at a wider variety of temperatures.
The exact smoke point of an oil depends greatly on how refined the oil is. Less refined oils smoke at lower temperatures while highly refined oils (generally the type you can buy in the grocery store) start to break down at much higher temperatures. Additionally, once an oil has been used it will have a slightly lower smoke point if it is reused. The smoke point also decreases if the oil has been stored for a long time or if there are any contaminants in the oil.
The smoke points of some common cooking oils and fats are shown below. Variations in temperature are due to the difference between unrefined and refined oils: