Causes of depression: genetics, environment, and others

last updated: Jun 08, 2021

5 min read

If you or someone you love has been diagnosed with depression, you may start to wonder why. Depression is a complex illness. Just because it develops, that doesn’t mean you did anything wrong.

There is a wide range of risk factors that may contribute to depression. Not everyone will develop depression even if they experience the same stressful events. Not everyone who does develop depression will experience it the same way.

Understanding the various causes of depression can help with preventing it. Still, no matter the cause, there are effective treatments to help you feel better.


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What is depression?

Depression is a group of mood disorders that leads to persistent feelings of sadness, low self-worth, and loss of interest. 

Our moods change throughout our lives. However, a persistent low mood and other symptoms of depression lasting longer than two weeks could be a sign of clinical depression (Chand, 2020). 

Untreated depression can lead to various physical and mental health problems, affecting your relationships, home life, and work life. 

Symptoms of depression

Depression symptoms vary from mild to severe. They often include (Chand, 2020):

  • Feelings of sadness

  • Low or depressed mood

  • Changes in appetite and weight

  • Changes in sleep (too much or too little)

  • Difficulty concentrating

  • Low motivation and loss of interest

  • Fatigue or low energy

  • Feelings of guilt and thoughts of worthlessness

  • Trouble completing daily tasks

  • Thoughts of death or self-harm

Types of depression

Often the different types of depression are generalized to simply be called depression. Still, there are multiple forms of depression, such as (Chand, 2020): 

All types of depression get similar treatment. A combination of antidepressants and psychotherapy help manage the symptoms of depression, no matter what kind of depression you may have. Still, understanding which type of depression you or a loved one has could help you understand the causes better.

Causes of depression

Depression is a complex mental disorder, and the exact cause of depression is unknown. Multiple factors likely play a role in developing depression, although some have a higher chance of triggering depression than others.

Depression is related to changes in brain chemistry for neurotransmitters that help to regulate mood. Neurotransmitters send messages between your nerves. Serotonin, dopamine, and norepinephrine are the neurotransmitters believed to affect depression and mood (Chand, 2020).


A family history of depression is a common risk factor for developing depression. No known single gene causes depression, unlike some other hereditary diseases. Still, it’s thought that genetics play a role in the likelihood of developing depression. 

Research shows that a family history of depression increases the chances of developing depression, no matter the other circumstances in your life (Colvin, 2014).


Certain medications have the side effect of causing low mood and may trigger depressive episodes. Medication-induced depressive disorder may be caused by medications such as (Bains, 2021; Kuan-Pin, 2019):

  • Steroids

  • Antihypertensives (high blood pressure medications)

  • Anticonvulsants (anti-seizure medication)

  • Interferon-alpha (an antiviral medication)

A drug used to treat acne, isotretinoin, can also trigger depressive symptoms. However, there's mixed research on the relationship between isotretinoin and depression. In one study, some people experienced lower moods while taking the medication. In contrast, others experienced an improved mood as their acne cleared (Bray, 2019). 


Experiencing loss or the death of a loved one is a stressful time that could increase the risk of depression. Coping with death is challenging, and research shows that grief may trigger depression in some people (Francis, 2015). 

Grief and loss can happen after many different life events, including divorce, children leaving home, retirement, losing a job, loss of a beloved pet, or any loss of an important goal.

Grieving is a normal process. The feelings of emptiness, sadness, or loneliness don't mean you will experience depression. Still, for some people, it may turn into depression if the feelings persist.

Chronic pain

When an injury or illness leads to pain that lingers for weeks or months, it can take a toll on your life. Chronic pain can affect sleep, exercise, relationships with others, and productivity.

Because of all the changes chronic pain can come with, it can lead to problems with self-worth, self-esteem, social isolation, and sadness. As a result, chronic pain can be associated with an increased risk of developing depression (Thom, 2019).

Medical conditions

Much like chronic pain, chronic health conditions can also increase the risk of developing depression (Thom, 2019). Chronic illnesses often last for years, though many are manageable with lifestyle changes and medications.

Still, for some, the long-term stress of managing a condition takes a toll on their mental health. Here are some of the chronic medical conditions often associated with an increased risk of depression (Bains, 2021; Thom, 2019):

Physical trauma or injury

Injury and physical trauma may increase the risk of depression. A sudden change in your physical abilities, such as a spinal cord injury following a car accident, can change how you perceive your place in the world. 

The sudden loss of mobility and the need to go through physical therapy can trigger depression in people at higher risk for depression, especially those with more severe injuries (Shih, 2011).

Emotional trauma and abuse

Living through traumatic events, like natural disasters, war, and physical, sexual, or emotional abuse, can make you more vulnerable to depression. Research shows that trauma increases the risk of depression if you don’t have access to helpful ways to cope with the emotions and experiences (Huh, 2017).

Substance use

Alcohol and drug abuse are strongly associated with depression. Around 25–30% of people with a substance use disorder are also experiencing depression (National, 2009).

Drugs and alcohol affect your brain chemistry and can leave you feeling better in the short term. But, over time, they negatively impact both your physical and mental health.


Insomnia and lack of sleep significantly increase the risk of depression. Research suggests people with insomnia are twice as likely to develop depression (Li, 2016). 

Consistently making a good night’s sleep a priority and treating insomnia could help to lower your risk for depression. Alternatively, if you have insomnia, finding ways to cope with stress and fight depression could help prevent sleep problems, as well (Li, 2016). 

Social Isolation

Social isolation and lack of a support group can also contribute to depression. Being cast out by family or friends can increase loneliness and take away support that protects against depression. Even just the perception of being alone can increase the risk of depression (Taylor, 2018).


Older adults are at a higher risk for social isolation and depression. They are at an even higher risk if they live alone and lack social support (Taylor, 2018). This may be the case because of the number of life experiences they have had, along with changes throughout their lives, such as loss of friends and family, retirement, and loss of mobility. 

Treatment for depression

Depression is a serious condition that can significantly impact people's lives. The good news is it can be treated with the help of mental health professionals. Typically, depression is treated with medications, psychotherapy, or combining the two (Chand, 2020).

Medications commonly used include antidepressants and mood stabilizers, such as:

Psychotherapy involves working with a trained mental health professional. Cognitive-behavioral therapy (CBT) and talk therapy are common forms of psychotherapy used to treat mental illness. They help you to cope with stress and give you strategies to help manage your emotions to feel better.

For severe depression, your healthcare provider may recommend procedures called electroconvulsive therapy (ECT) or transcranial magnetic stimulation (TMS). Both procedures stimulate the brain to help adjust brain chemicals to help improve depression. 

If you or a loved one is experiencing depression or thoughts of suicide, there is help available. The Substance Abuse and Mental Health Services Administration (SAMHSA) National Helpline is a free, confidential hotline. It’s available 24/7 to provide support and connect you with local services at 1-800-662-4357.


If you have any medical questions or concerns, please talk to your healthcare provider. The articles on Health Guide are underpinned by peer-reviewed research and information drawn from medical societies and governmental agencies. However, they are not a substitute for professional medical advice, diagnosis, or treatment.

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How we reviewed this article

Every article on Health Guide goes through rigorous fact-checking by our team of medical reviewers. Our reviewers are trained medical professionals who ensure each article contains the most up-to-date information, and that medical details have been correctly interpreted by the writer.

Current version

June 08, 2021

Written by

Ashley Braun, RD, MPH

Fact checked by

Steve Silvestro, MD

About the medical reviewer

Dr. Steve Silvestro is a board-certified pediatrician and Associate Director, Clinical Content & Education at Ro.