Michael Mosely From Trust Me I'm a Doctor says
The secret to reheating is to do it thoroughly. Most of us tend to use a microwave oven to reheat food, but there is a problem. A microwave oven will heat your food unevenly, leaving cool pockets where bacteria can thrive. That is why it is important that you take the food out, part of the way through cooking, give it a good stir, and then zap it again. Your aim is to get every part piping hot.
One food that people are particularly cautious about reheating is rice. As I mentioned above, most cases of food poisoning are caused by bacteria, but in the case of rice it is a bit more complicated than that.
Rice can be contaminated by a bacterium called Bacillus cereus. The bacteria themselves are killed by heat, but they sometimes produce spores that are not only toxic but surprisingly heat resistant.
This can lead to "fried rice syndrome", so-called because it was once not uncommon for people to get ill after eating fried rice at a Chinese buffet (where fried rice dishes had been left sitting around at room temperature for many hours). These days hygiene standards in Chinese restaurants are much better than they were.
Despite widespread fears, it is safe to reheat rice, and I frequently use rice left-over from the night before as part of a stir fry, but not if you have left that rice out overnight in a warm kitchen. As with meat, once the rice has been cooked you should aim to cool it and keep it cool as quickly as possible.