Contrary to popular belief, leftover food should be reheated only once. Reheating food more than once increases the risk of bacteria multiplying on the food, which leads to a greater potential for food poisoning.
Another issue with repeatedly reheating foods is that bacteria may survive each time the food is heated due to improper heating. When heating food, especially in the microwave, it is essential to ensure that the food is heated thoroughly in order to kill any bacteria that may be present. Otherwise, those who eat the food may get food poisoning, a possibly life-threatening illness caused by food-borne organisms.