A flick of the wok and a burst of flame—most chefs use the "flaring up" technique when stir-frying. Many find this move particularly cool and diligently practice it at home. Little do they know that flaring up the oil doesn't significantly enhance the flavor; instead, it increases the production of carcinogens.
Generally, the longer and higher the temperature of cooking oil, the more harmful substances and carcinogens are produced. This is the very reason why fried foods may contain carcinogens. Compared to deep-frying, when the oil itself catches fire, the temperature is, of course, much higher, even exceeding 300°C, making it easy for carcinogens like benzopyrene to form. These attach to the food and seriously harm human health. Besides carcinogens, "flaring up" also produces trans fatty acids. It's worth noting that the longer the oil is heated, the more harmful byproducts are created.
Additionally, the oil temperature should not be too high throughout the entire stir-frying process. There's a method to help you judge if the oil temperature is right: toss a small piece of scallion into the wok. If it bubbles vigorously around the scallion, the temperature is ready for cooking. If the scallion changes color or even burns, it means the temperature is too high.
When eating at home, the priority is health and safety. Why risk the health of your family and yourself for a flashy but impractical technique?