1. Chicken
Chicken and other poultry have a certain amount of salmonella contamination as standard, as do eggs.
This can be a problem with reheating in microwaves in particular, which does not penetrate all areas of a food as equally as heatwaves. That means some parts of the food cook faster than others.
It is important particularly with chicken to turn the meat frequently to ensure even heating inside and out.
Reheating chicken is not advisable more generally because it has a higher density of protein than red meat – when reheated, proteins break down differently and can upset the stomach.