Anger is a term for the emotional aspect of aggression, as a basic aspect of the stress response in animals whereby a perceived aggravating stimulus "provokes" a counterresponse which is likewise aggravating and threatening of violence. Very mild types of anger are typically described as "distaste," "displeasure", or "irritation," while "rage" refers to an extreme degree of anger associated with a loss of calmness or discipline (in the case of human conduct).

Often based in a sensation or perception of threat, anger can be considered an emotional component in the increased threat response (part of the broader "stress response") whereby the charged emotional state produces physiological effects (increased adrenaline, cortisol), thereby producing behavioural effect of heightened stress and aggression.

Anger may be "provoked" (or triggered) by perceived threats, like conflict, or by abstract concepts such as injustice. There are many physical conditions that increase the potential for one to become angry. Common contributors to irritability include fatigue, hunger, being in pain, sexual frustration, or recovery from an illness. Other causes are hormonal changes, such as those associated with PMS, giving birth, and menopause, physical withdrawal, and bipolar disorder. Research also shows that some individuals can be genetically predisposed to higher levels of anger.

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