Evidence suggests that the weeks preceding the onset of a manic episode are usually marked by an increase in frequency of stressful life events in the individual's life. Stressful life events have also been shown to trigger higher rates of relapse amongst individuals who have recovered from previous episodes. Bipolar individuals with an extroverted personality are less likely to relapse, suggesting that these individuals may have a greater ability to maintain a supportive social network that contributes to their ability to cope with the disorder. Individuals who are surrounded by an environment or family high in criticism and hostility--high in expressed emotion (EE)--are more likely to relapse shortly after discharge.

The leading psychoanalytic theory concerning the etiology of bipolar mood disorders asserts that both depressive and manic episodes result from a low self-concept. Depressive episodes reflect this directly. Manic episodes represent a defense against the low self-concept by acting in the opposite direction, a type of reaction formation. Proof for this theory comes from cognitive research that has shown that bipolar patients in a manic episode explicitly report higher ratings of self-esteem than bipolar individuals in a depressive episode, ratings similar to those of individuals without any mood disorders. Yet, on implicit measures, bipolar patients exhibit lower self-esteem ratings in both manic and depressive episodes compared to normal controls.

Genes have been shown to account for much of the vulnerability factor for developing bipolar mood disorder, accounting for about 80 percent of the variance in vulnerability. The concordance rate for monozygotic twins is about 69 percent and about 19 percent for dizygotic twins. The risk is much higher for individuals with a relative who express the disorder; yet it is unclear what exactly is being inherited. Among the relatives of bipolar probands, the risk for both bipolar and unipolar mood disorder is much higher than for individuals in the general population. Family studies also indicate that bipolar mood disorder should be considered a separate disorder from unipolar mood disorder, since the risk for developing bipolar is higher among the family of those individuals with bipolar disorder.