The presence of bacteria such as nitrifying bacteria in pickled food will cause nitrates to be converted into nitrites, and excessive intake of nitrites will lead to poisoning, cancer or death. As the process of pickling aquatic products, vegetables and meat cannot be sterilized by boiling at high temperature, and as the pickling process is not absolutely aseptic, it may cause the proliferation of microorganisms such as nitrifying bacteria, Escherichia coli, Corynebacterium diphtheriae, yeast, etc., which will reduce nitrate, which is widely present in food, to nitrite, which will then be accumulated in the food. When a large number of intake of pickled food and other food containing nitrite, it will cause a large amount of nitrite intake in a short period of time, causing poisoning, manifested as respiratory distress, decreased blood pressure, impaired consciousness, etc., and severe poisoning will lead to death. In addition, nitrite is a strong carcinogenic substance, with nasopharyngeal cancer, esophageal cancer and other diseases. It is recommended to have a balanced and reasonable diet in daily life and avoid single intake of pickled food; if the above mentioned symptoms of poisoning occur, it is recommended to go to the hospital in time for medical treatment.