Extra virgin olive oil is the best quality of olive oil. It contains a high concentration of unsaturated fatty acids, polyphenols and some other substances, that are claimed to have a positive effect on human health. Some of these substances are sensitive to heat. Upon heating some of the health promoting properties of this oil are thus lost.

All fats that are heated may be partially degraded and oxidized. This may eventually result in toxic components. Fats with a high percentage of unsaturated fatty acids are more prone to this oxidation than fats with only saturated fatty acids. Olive oil has a high percentage of unsaturated fatty acids and is thus suitable for one-time frying or baking, but not for prolonged or multiple heating.

The use of extra virgin olive oil for frying or baking thus is not recommended, but not because of toxicity, but due to the loss of its good properties during heating. It is more suitable for dressings or other applications that do not require heating.