Depression as of now do not have any main cause, it may be caused by serious medical illness, it may be caused by life changes such as lost of loved once or change in location, it can as be a result of family history. It can make your mood swing for no known reseaon.
Source
Here are some causes of depression
Abuse:
A physical, sexual or emotional abuse can make a person more vulnerable to a depressed life.
Death or a loss :
Grief or sadness after the death or loss of loved ones can also cause depression.
Personal problems:
social isolation due to other mental illnesses or being cast out of a family or social group can contribute to the risk of developing depression.
Effects of depression on human
Weight gain or weight loss
trouble sleeping
Chronic pain
Heart diseases
Sexual health problems
Ways of managing depression
Get enough sleep
Eat well and
Exercise regularly.
