In vegetable ingredients, due to overnight exposure to the air, some bacteria appear to be fermented, and combined with the salt of vegetables, nitrite is generated. Nitrite is produced by the work of gastric acid, and nitrosamine is the real carcinogenic component.
Of course, it takes a long-term and large-scale continuous intake of nitrite to cause cancer. For example, eating more than 1 kilograms of overnight vegetables every day may reach a carcinogenic dose.
It is false that overnight dishes cause cancer, but it does not mean that eating overnight dishes is a healthy habit. Overnight dishes will be eroded by a large number of microorganisms, which will easily lead to diarrhea and the possibility of gastrointestinal infection. From this point of view, it is recommended that you cook and eat fresh vegetables now.