Causes:
1. Stressful events such as bereavement or a relationship breakdown
2. Illness such as life-threatening illness.
3. Personality such as low self-esteem
4. Giving birth Some women are particularly vulnerable to depression after pregnancy.
5. Loneliness Becoming cut off from your family and friends.
6. Alcohol and drugs.
7. Abuse such as emotional abuse.
8. Certain medications such as acne drugs.
9. Conflict such as personal conflicts with family members or friends.
10. Genetics. such as family history of depression.
11. Hormones. Changes in the body's balance of hormones may be involved in causing or triggering depression. Hormone changes can result with pregnancy and during the weeks or months after delivery (postpartum) and from thyroid problems, menopause or a number of other conditions.
12. Environmental Factors such as Social isolation.
13. Psychological causes can trigger depression such as frustration.
References:
1. http://www.nhs.uk/Conditions/Depression/Pages/Causes.aspx
2. http://www.depressiontoolkit.org/aboutyourdiagnosis/depression.asp
3. http://www.webmd.com/depression/guide/causes-depression
4. http://www.mayoclinic.org/diseases-conditions/depression/basics/causes/con-20032977
5. http://depressionhurts.ca/en/about/causes.aspx
6. http://www.helpguide.org/articles/depression/depression-in-women.htm
7. http://www.pdrhealth.com/diseases/depression