Whether stir-frying in an old cast iron skillet is harmful to the body depends mainly on whether the iron skillet is rusty and whether it is cleaned thoroughly before use, as follows. If the old cast iron skillet is not rusty, stir-frying with iron skillet generally does not produce significant harm to the human body. However, if the iron pot has rusted, and not thoroughly cleaned directly stir fry, will lead to long-term intake of large amounts of rust, thereby increasing the metabolic burden on the liver, the liver function to cause some damage. In addition, iron pot rust is due to iron oxidation reaction to form iron oxide, iron oxide is ingested by the human body, will react with gastric acid, may also aggravate the burden on the gastrointestinal tract, stimulate the gastrointestinal mucosa, a large number of intake is also prone to nausea, vomiting, indigestion, abdominal pain, diarrhea and other discomforts. Therefore, for serious rust, black slag, black skin of the iron pot, should not be used again.