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What Causes Depression?

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Depression is often due to a chemical imbalance in the brain, but there are a number of reasons why depression can develop. (1,2) 

According to the World Health Organization, more than 264 million people of all ages around the world are depressed. (3) While two people may experience the same symptoms, the underlying cause of their symptoms may be completely different. Additionally, one person’s depression may have been caused by multiple factors at the same time (for example, someone may have had multiple stressful life events, or they may have a biological predisposition to depression as well as experiencing a traumatic event). 

What are some common known risk factors for depression?

Trauma and Situational Stress

One study showed that traumatic events are the #1 cause of depression and anxiety. (4,5) Major life changes, although not necessarily considered a trauma, can also trigger extreme stress and lead to depression. 

Traumatic life events can include:

  • Witnessing or being a part of a serious accident
  • Childhood abuse (sexual, physical, or emotional)  (6,7)
  • Natural disasters
  • Bullying 

Major life changes can include:

  • The loss of a loved one
  • Losing one’s job
  • Retirement
  • Divorce
  • Financial problems

PTSD (post-traumatic stress disorder) can occur after a traumatic event and is often diagnosed with depression. People who are diagnosed with PTSD are 3 to 5 times more likely to develop depression compared to people who do not have PTSD. (8)


Sometimes it may seem there is no clear reason why someone has depression. If you’re feeling depressed, and have had family members who have also struggled with depression, this is no coincidence. It’s very common for depression to run in families. If you have a parent, brother, sister who has been diagnosed with depression, you’re 2 to 3 times more likely to develop depression compared to someone who does not have a parent or sibling with depression. (9)

Scientists have discovered 269 genes associated with depression. (10) However, just because someone may inherit a gene associated with depression, that doesn’t mean that they will develop the condition. 

Irregularities in the Brain

Scientists have linked chemical imbalances and physical abnormalities of the brain to depression. Certain chemicals called neurotransmitters help send signals throughout the brain, helping it to perform all of its functions properly, including mood regulation. Some examples of neurotransmitters known to be associated with depression when imbalanced include serotonin and dopamine. (11)

Scientists have also identified physical differences in the brains of people who are depressed compared to people without depression. After looking at MRI images of the brain for both healthy patients and patients with depression or anxiety, researchers observed differences in a structure called gray matter. Gray matter is primarily made up of nerve cells. (12) This supports the idea that differences in the brain may be related to depression.

Why Do Some People Get Depressed While Others Don’t?

You may have noticed a situation where two people have been affected by the same trauma, but one person may develop depression while the other one doesn’t. Just because someone experiences a risk factor for depression does not guarantee that they will be depressed. How a person reacts to stress and someone’s personal thinking style contributes to whether or not they will develop depression. (4,5)

Depression Treatment in NYC

The many reasons why depression can develop may explain why one depression treatment doesn’t work for everyone. This is why depression treatment often requires a trial-and-error approach. If you’re interested in learning more about depression treatments in NYC, visit our website


1.aan het Rot M, Mathew SJ, and Charney DS. Neurobiological mechanisms in major depressive disorder. CMAJ. 2009;180(3):305-13. Accessed January 11, 2020.

2. Hammen, C. Risk Factors for Depression: An Autobiographical Review. Annu Rev Clin Psychol. 2018;14:1-28. Accessed January 11, 2020.

3. Depression. World Health Organization. Published December 04, 2019. Accessed January 11, 2020.

4. Kinderman P, Schwannauer M, Pontin E, and Tai S. Psychological processes mediate the impact of familial risk, social circumstances and life events on mental health. PLOS One. 2013;16;8(10):e76564. Accessed January 09, 2020.

5. University of Liverpool. Traumatic life events biggest cause of anxiety, depression. Science Daily. Published October 16, 2013. Accessed January 11, 2020. 

6. Shapero BG, Black SK, Liu RT, et al. Stressful life events and depression symptoms: the effect of childhood emotional abuse on stress reactivity. J Clin Psychol. 2014;70(3):209–223. Accessed January 09, 2020.

7. Negele A, Kaufhold J, Kallenbach L, Leuzinger-Bohleber M. Childhood trauma and its relation to chronic depression in adulthood. Depress Res Treat. 2015;2015:650804. Accessed January 11, 2020.

8. Kessler RC, Sonnega A, Bromet E, Hughes M, and Nelson CB. Posttraumatic stress disorder in the National Comorbidity Survey. Archives of General Psychiatry. December 1995;52(12):1048-60. Accessed January 11, 2020.

9. Lohoff FW. Overview of the genetics of major depressive disorder. Current Psychiatry Reports. December 2010;12(6):539-546. Accessed January 11, 2020.

10. Howard DM, Adams MJ, Clarke TK, Hafferty JD, Gibson J, Shirali M, Coleman JRI, Hagenaars SP, Ward J, Wigmore EM, Alloza C, Shen X, Barbu MC, Xu EY, Whalley HC, Marioni RE, Porteous DJ, Davies G, Deary IJ, Hemani G, Berger K, Teismann H, Rawal R, Arolt V, Baune BT, Dannlowski U, Domschke K, Tian C, Hinds DA, Trzaskowski M, Byrne EM, Ripke S, Smith DJ, Sullivan PF, Wray NR, Breen G, Lewis CM, and McIntosh AM. Genome-wide meta-analysis of depression identifies 102 independent variants and highlights the importance of the prefrontal brain regions. Nature Neuroscience. 2019;22(3):43–352. Accessed January 11, 2020.

11. What causes depression? Harvard. Published June 2009. Updated June 24, 2019. Accessed January 13, 2020. 

12. Radiological Society of North America. MRI uncovers brain abnormalities in people with depression, anxiety. ScienceDaily. Published November 20, 2017. Accessed January 11, 2020.

Dr. Woo has been seeing patients in private practice since 2002, always with the goals of combining evidence-based medicine with psychodynamic psychotherapy and collaborating with other mental health professionals to ensure the best possible outcomes for his patients. He has been certified to administer TMS at his practice since 2017. His greatest clinical interests include helping patients suffering from depression, anxiety, and obsessive compulsive disorder.

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