Risk perception is due to a subjective evaluation of reality and depends on a number of factors such as: individual coherence and flexibility, the set of social values and rules that contributed to the definition of the individuals' interior world - this does not always make proper risk perception possible. Even though the way common people set-up their own judgment is based on their own interpretation tracks, surely different from expert criteria, we cannot label their approach as irrational. Over time, through an evolutionary process, people have decided what is safe and what is dangerous; this personal awareness was not based on the science but on experiences, images, feelings and emotions. Most of the time, neither social nor economical conditions can prevent people to feel an epidemic risk in the same way as it was felt during the plague of 1350. Most of the time, after a disaster, victims experience a regression so, for example, even if it is known that corpses do not always cause infections, after the tsunami disaster, most of the bodies were quickly cremated by scared survivors; this made the identification and burial of the victims impossible.