One of the several ways in which affect may influence cognition is when people use affect as a source of information about external events. Emotional reasoning, ex-consequentia reasoning, and affect-as-information are terms referring to the mechanism that can lead people to take their emotions as information about the external world, even when the emotion is not generated by the situation to be evaluated. Pre-existing emotions may thus bias evaluative judgments of unrelated events or topics. From this perspective, the more people experience a particular kind of affect, the more they may rely on it as a source of valid information. Indeed, in several studies, it was found that adult patients suffering from psychological disorders tend to use negative affect to estimate the negative event as more severe and more likely and to negatively evaluate preventive performance. The findings on this topic have contributed to the debate that theorizes the use of emotional reasoning as responsible for the maintenance of dysfunctional beliefs and the pathological disorders based on these beliefs. The purpose of this paper is to explore this topic by reviewing and discussing the main studies in this area, leading to a deeper understanding of this phenomenon.