The danger of eating leftovers to human body depends on whether the leftovers are spoiled or not. If the leftovers are not contaminated by microorganisms, they are generally not harmful to human body after eating them. Leftovers in non-low-temperature storage conditions can contaminate a large number of bacteria, which may lead to abdominal pain, nausea, vomiting and other gastroenteritis symptoms in the body after consumption. Long-term regular consumption of leftovers will also risk an increase in nitrite, and food poisoning may occur after consumption, therefore, spoiled leftovers should not be eaten. As bacteria are widely present in the air, dishes, kitchen, refrigerator and other places, if leftovers are left for a long time, it will give bacteria and mold enough time to reproduce, in addition to reducing the nutritional value of food, there is also the possibility of food poisoning. In addition, nitrite is mainly produced by the combination of salt and minerals in leftovers, the longer it is placed, the higher the nitrite content, in general, leftovers into the refrigerator 6 hours later, the nitrite content in the meal has exceeded the national standard, placed 18 hours later, the nitrite growth can reach 4 times, placed 24 hours, the nitrite content seriously exceeded the standard, not suitable for consumption. Therefore, it is recommended that each meal as far as possible in the current meal, do not stay until the next meal, if you want to stay until the next meal to eat, it is recommended to place the refrigerator to save, and separate from other food placed in 6 hours to eat, do not place the meal more than 24 hours.