In psychology, aversives are unpleasant stimuli that induce changes in behavior through punishment; by applying an aversive immediately following a behavior, the likelihood of the behavior occurring in the future is reduced. Aversives can vary from being slightly unpleasant or irritating (such as a disliked color) to physically damaging. It is not the level of unpleasantness, but rather the effectiveness the unpleasant event has on changing behavior that defines the aversive.