Scientists believe that recurring (as opposed to singular non-recurring) bipolar disorder may be caused by a combination of biological and psychological factors. Most commonly the onset of this disorder can be linked to stressful life events. According to the "Kindling theory" and possibly assumed, periods of depression, mania, or "mixed" states of manic (euphoric) and depressive symptoms typically recur and may become more frequent, often disrupting work, school, family, and social life. It is possible to see single occurences of depression and mania which do not recur.The "kindling" theory suggests that persons who are genetically prone toward bipolar disorder experience a series of stressful events, each of which lowers the threshold at which mood changes occur. Then at some point these mood changes occur spontaneously. The person then "becomes bipolar". This might explain why the cause of bipolar disorder is difficult to pinpoint but is somehow related to genetic and/or genetic and enviromental causes. People can also be "prone" to bipolar disorder after substance abuse, or because of a neurological condition or brain damage. However, if drug abuse can be linked to bipolar symptoms, they may not recur.
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