In psychology, aversives are unpleasant stimuli that induce changes in behavior via negative reinforcement or positive punishment. By applying an aversive immediately before or after a behavior the likelihood of the target behavior occurring in the future is reduced. Aversives can vary from being slightly unpleasant or irritating to physically, psychologically and/or emotionally damaging. It is not the level of unpleasantness or intention that matter, but rather the level of effectiveness the unpleasant event has on changing (decreasing) behavior that defines something as aversive.