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, recovery from an illness, or the use of certain drugs. 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.