Bipolar disorder affects around 2.9% of the population annually. It can develop at a young age and the average age of onset is 25. Genetics, brain structure, and stress may contribute to its causes, though the specific cause is unknown. There are four main types defined by symptoms: bipolar I involves manic and depressive episodes; bipolar II involves hypomania and depression; cyclothymic disorder involves shifting mood states; and bipolar disorder other/unspecified involves mood changes not meeting other criteria. Treatment involves medications, psychotherapy, electroconvulsive therapy, and self-care practices.