Please explain what are the causes of depression?

Many causes: This is a huge topic -- but there may be biological causes like neurotransmitter changes, hormone changes, medication side effects, etc. Medical illnesses that increase likelihood. Also genetic causes since depression can be more common in certain families. Life events like loss of any kind. Childhood trauma and abuse. Drug and alcohol abuse. For more info: http://tinyurl.Com/36yv6hs.

Depression: Biopsychosocial factors, mainly genetic (biological), self concept & esteem issues (psychological) and stress (social). This is one model, simplified to explain causes of depression.