When does heating olive oil become “carcinogenic”?

Olive oil is used in kitchens across the UK, but there is often confusion around which oil to use when cooking. When it comes to frying, baking and drizzling, which oils should we use and which should be avoided? The debate over smoke points and olive oils becoming carcinogenic is a topic of conversation that is frequent. Should we all be using coconut oil, or is olive oil the best? To settle the debate, we investigated the research.

Olives and olive oil
Olive oil, perfection.

Extra virgin olive oil has been linked to improved heart health and is a staple in the Mediterranean diet. It is rich in phenolic antioxidants and monounsaturated fats which are shown to improve heart health. Most of all, extra virgin olive oil’s distinct flavour makes it a great oil to use in the kitchen. So, why the negative press?

The fear comes from an oils smoke point. When oils are cooked past their smoke point, they release chemicals which can be harmful. Consumers are concerned that if they cook with olive oil or extra virgin olive oil that any original health benefits would be destroyed, or become toxic.

Extra virgin olive oil is the most chemically stable oil after heating at high temperatures, and safe to consume.

Acta Scientific Nutritionl Health – 2018

What the research says

Research published in 2018 by Acta Scientific Nutritional Health found that when compared to other popular cooking oils, extra virgin olive oil was the most chemically stable after heating at high temperature. In addition, despite being exposed to extreme heat it was still safe to consume. The tests consisted of a 20-minute frying at 240C and a 6-hour deep fry at 180C.

In both tests extra virgin olive oil came out on top with the most stable of all oils. In addition, it produced the lowest number of by-products such as free fatty acids. Coconut oil and other virgin oils such as avocado oil came close behind for stability and smoke point.

It demonstrated that oils must be heated at extreme temperatures for long time periods to show any degradation. Even still, the healthier the oil, the more stable it behaves. High stability of an oil slows the breakdown and release of toxins which may be a health concern. To put this into consideration, the Food and Chemical toxicity study (2010) found that when olive oils had to be fried for 24 – 27 hours to be considered harmful. This is above and beyond times and temperatures you would roast potatoes for in your kitchen.

Added antioxidant benefits

The research also suggested that cooking antioxidant rich foods in olive oil also provided extra health benefits. The Food and Chemistry study (2015) found that when deep frying vegetables (tomatoes, aubergine and squash) the antioxidant levels of the food increased. This highlighted that despite heating, olive oil continued to deliver nutritional benefits even when deep fried.

Other factors to bear in mind

When smoke points are measured, these are done in laboratories, an enclosed environment with small amounts of oil to test. Exposure to air and amount of oil used when cooking can increase an oils smoke point. This means that by the time the oil reaches your pan at home, the smoke point is likely to be above what is stated.

An olive tree with light green olives growing
An olive tree, prior to pressing for olive oil.


Although smoke points highlight how an oil responds to heat, it is not an indicator of stability or health value. Oil stability depends on the levels of antioxidant’s and monounsaturated fats, not the smoke point. Extra virgin olive oil is the most stable and healthiest oil on the market. Despite coconut oil coming second in the Acta study, its high saturated fat content make it a lesser choice to use in the kitchen. Opting for avocado oil and rapeseed oil would be another great option to use in the kitchen.

Nutrition and Cake is a Nutrition business - Run by Registered Nutritionists Hannah and Elysia, they provide Nutrition Education to help others lead a healthy, balanced lifestyle.