Disruptive disorders of childhood are not well understood. Children do not set out to be difficult. Childhood misbehavior is a nonspecific response to many internal and external disturbances, and defiance is even appropriate at some stages of development. No single cause of ODD has been identified, and while the condition tends to run in families, no genetic patterns have been identified. Biological, social, and childrearing factors all seem to play a role in ODD.
Some research identifies two different types of ODD that may have different roots. One, more reactive, is marked by irritability, associated with internalizing conditions such as anxiety, and fueled by poor frustration tolerance and problems of emotion regulation. The other, more proactive, is most marked by argumentativeness and vindictiveness, associated with externalizing conditions such as conduct disorder, and is linked to neurobiological makeup including low heart rate and low stress reactivity, both signs of underarousal of the autonomic nervous system.