Updated and reviewed: June 4th, 2026
What Causes Depression?
There is not one simple cause for depression. Many medical conditions have a more straightforward cause. For example, viruses cause colds. Depression is more complex. Depression usually develops through a combination of genetic, social, environmental and psychological factors.
Research shows that several factors make some people more vulnerable to depression than others. Relevant factors include genetics, childhood experiences, as well as the meaning we ascribe to life events or circumstances.
Biological Causes of Depression
Genetics and family history
Studies suggest that somewhere between 35% to 50% of one’s risk for depression comes from genetic factors. Having a genetic vulnerability does not mean someone will develop depression. Instead, genes appear to influence susceptibility, which then interacts with life experiences and other risk factors.
Genetic factors are with us since birth, and are present whether or not our father or mother suffered from depression. There is not one gene for depression like there is for some other conditions (e.g., cystic fibrosis). Instead, multiple genes are suspected to play a role.
If your father or mother suffered from depression, your risk of depression is indeed higher. However, it is difficult to say whether that’s due to genetic factors or environmental ones. And it is possible to have one or two parents who suffered from depression, and have a genetic vulnerability to depression, and not suffer from depression. This can happen due to protective factors (described below), or perhaps to chance.
Brain chemistry and neurotransmitters
At points in the 1980s and 1990s, it became popular to speak about depression as caused by a “chemical imbalance.” There were two reasons for this:
- Scientists at that time were learning more about the role of neurotransmitters (naturally occurring chemicals in the brain) in depression.
- It is destigmatizing to think about depression as caused by factors beyond the control of the depressed person — it removes any blame.
The success of Prozac in the early 1990s further supported this understanding of depression. Medications like Prozac, Zoloft, and other SSRIs can improve symptoms of depression by affecting neurotransmitter function in the brain.
However, depression is not usually as simple as the phrase “chemical imbalance” might suggest. Depression can be caused by unhealthy thinking patterns, by neurotransmitter dysfunction, other disorders, medical conditions, sociocultural issues, environmental issues, or any combination of the above.
Sometimes the cause of depression is quickly clear to a treating professional despite being a mystery to the depressed person. The cause? Another disorder. Read on to learn how this can happen.
Hormonal changes
Your body’s biochemical functioning can be an important contributor to depression. The hormonal changes that follow childbirth can cause significant depression for mothers. This type of depression can be serious. It is challenging because the mother is often facing new stressors and changes in her life precisely when the hormonal changes are having their greatest impact.
Another factor that makes postpartum depression dangerous is that it can be quite long-lasting. This is a problem if after a few months friends and family assume that a mother should be “fine now” — but often that’s just not true. Postpartum depression can last at least three years for some women. Sadly, such uninformed attitudes from loved ones can worsen the depression.
Medical conditions that can contribute to depression
Sometimes medical conditions can directly or indirectly cause or worsen depression.
- Chronic pain: conditions such as fibromyalgia and arthritis that cause chronic pain can contribute to depression.
- Thyroid disorders: hypothyroidism, which affects 5% to 10% of the population, can cause depression. Hashimoto’s disease is common cause of hypothyroidism.
- Neurological conditions: Stroke, Parkinson’s Disease, multiple sclerosis and concussions all can cause depression.
- Sleep disorders: People with chronic insomnia are much more likely to have depression than other people, although it’s not clear which of those two conditions is likely to cause the other. People with sleep apnea are also more likely, statistically, to have depression than other people are.
Psychological Causes of Depression
Negative beliefs and schemas
One aspect of how you think that can lead to or worsen depression is the way you see yourself. If think of yourself as someone who is annoying, hard to like, or burdensome to others, you will be more vulnerable to depression. Beliefs like these, when considered as a group, are called schemas. We all have schemas — schemas are not inherently unhealthy. However, if they portray overly critical or negative views about yourself, they can cause depression. One school of thought contends that if schemas paint a picture of you as helpless, unlovable, or incompetent, then you are especially vulnerable to depression and anxiety.
Negative schemas are typically not something we’re born with, although that is difficult to prove scientifically. Schemas take shape via a combination of inborn factors and learned experiences. These experiences can happen in childhood or adulthood. For example, if a college student starts to have a lot of success in school that she didn’t have before, she may start to see herself as smarter and more capable than in the past.
Rumination and repetitive negative thinking
If you think something that makes you sad, but then move on to other topics, your sadness is likely to be brief. However, if you tend to dwell on topics that cause make you feel sad, your vulnerability to depression goes up. This type of repetitive thinking is known as depressive rumination, and is a powerful force in influencing our mood.
Learned patterns of interpreting life events
How we interpret the things that happen in our lives can go a long way toward determining our risk for depression.
Consider the example of a breakup of a romantic relationship. Breakups can be painful — among the most emotionally painful experiences we have. If your tendency is to think about breakups as proof of your unworthiness as a romantic partner, you are likely to become depressed. On the other hand, if you are someone who tends to expect positive things in life, you might anticipate that you’ll be better off after a breakup. Our expectations and patterns of thinking contribute significantly to our risk for depression.
Social and Environmental Causes of Depression
Social isolation and loneliness
People who are lonely are at least twice as likely as others to become depressed. There is a robust body of research establishing the mental health and physical health benefits of having healthy social connections. Depression becomes more likely if someone is socially isolated. People are social animals, and when someone doesn’t have social connections or doesn’t feel part of a community, they often suffer because of it. They don’t have access to the same emotional support they otherwise would. And they become less likely to make healthy choices about their physical and mental health.
Generally speaking, if you feel like you belong, and feel like you have the support and care you need from others, your mental health will be better and you’ll be less likely to become depressed.
Relationship problems
Problems in one’s close relationships can also leave you at higher risk for depression. Relationship problems can leave you feeling more isolated (see above) and reduce your sense of self-worth. Reduced self-worth is actually a symptom of depression.
Major life changes
Some changes in life have a major emotional impact on us. Losing a loved one, losing a job, and retirement are just a few examples of life transitions that can affect us emotionally. It’s only natural to experience some symptoms of depression following the death of a close family member or friend.
However, changes in life such as losing a job or moving to a new place do not necessarily lead to depression. For some people changes like these won’t cause any depression — it depends on the situation, the severity of the change, and the person’s schemas, as described above. It’s more accurate to say that a life change triggered an episode of depression (just as going to college can trigger weight gain but doesn’t cause it).
Why Do Some People Become Depressed While Others Do Not?
One of the most puzzling aspects of depression is that the same experience can affect different people in very different ways. For example, two people might go through a difficult breakup, lose a job, or face a major health challenge. One person may become depressed, while the other experiences sadness and stress but does not develop depression.
Why does this happen?
Researchers believe the answer lies in the interplay of various risk factors and protective factors. Some people have a greater vulnerability to depression due to the factors described above: genetics, brain chemistry, hormonal factors, or medical conditions. Others may be more psychologically vulnerable because they tend to interpret setbacks in especially harsh or self-critical ways. Social factors such as isolation, financial stress, lack of support, or chronic conflict can also increase risk.
Many people assume the life circumstances or events themselves cause depression. This is sometimes true. However, it is perhaps just as likely that the way we think about those things causes us to cope well or to become depressed.
Protective factors against depression
Protective factors can have the opposite effect. Strong relationships, healthy coping skills, meaningful activities, physical health, adequate sleep, limited substance use, regular exercise, and a tendency toward flexible thinking can help people recover from difficult experiences without becoming depressed.
For example, imagine two people who are both laid off from work. One person might think, “This proves I’m a failure and I’ll never find another good job.” Another might think, “This is disappointing, but I have gotten through difficult situations before.” The first person is likely to experience more hopelessness and depression than the second.
This does not mean that depression is simply a matter of attitude or willpower. Rather, it illustrates how our thoughts, life experiences, and environment work together to influence our emotional well-being. Depression usually develops not because of a single cause, but because multiple risk factors outweigh the protective factors in a person’s life.
Understanding this can be reassuring. Why? Because if depression has many causes, then there are often many opportunities for treatment and recovery as well.
Mental Health Conditions That Can Contribute to Depression
OCD and depression
OCD is actually a quite varied condition that can cause depression in multiple ways. For example, many people with OCD spend significant amounts of time ruminating about the topic of their obsessions. This becomes unhealthy, unpleasant, and time-consuming for them. These effects of rumination can lead to depression.
Another way that OCD can cause depression involves compulsions. For example, if someone with OCD needs to touch something 16 times before leaving a room, this can lead to frustration and embarrassment. Over time these difficulties can lead to depression.
PTSD and depression
Depression has long been associated with PTSD. Until 2013, PTSD was thought of as causing depression. However, with the introduction of the fifth edition of the DSM (the widely used text used by mental health professionals to diagnose mental disorders) in 2013, we now understand depression is a part of PTSD. Not everyone with PTSD experiences depression, but around half of those with PTSD are also depressed.
This close relationship between PTSD and depression means that everyone who has major depressive disorder should also be screened for PTSD. If you are currently dealing with depression, we encourage you to ask your mental health provider about this.
Substance use and depression
Depression can cause substance abuse. However, substance abuse can also lead to depression. In fact, it’s common for either to cause the other. Often this happens as someone begins to grasp how much their substance use has come to impact, or even define, their life. The process of realizing that your relationship with a substance has become one of dependence can induce hopelessness and depression.
Additionally, substance abuse makes recovery from depression more difficult, leading to further frustration and worsened depressive symptoms.
Agoraphobia and depression
A 2014 clinical research study suggests that approximately 10% of people with major depressive disorder have or have had agoraphobia in the past. For any of us to avoid depression, we need to engage in regular mood and health-maintaining activities. Agoraphobia strips people of the ability to be as active as they were and often prevents them from seeing friends, going to parties, concerts, or restaurants. It’s easy to see why this would leave someone vulnerable to depression.
When to Seek Help for Depression
Depression can be a slow drag on your life, a major blockage, or anywhere in between. If you notice that depression is getting in the way of leading the life you’d like, or has been going on for too long, it’s good to seek professional help. Similarly, if you find that you struggle to enjoy things, ruminate about things that leave you feeling hopeless, or have thoughts of death, consult with a mental health provider. (Call 911 if you have thoughts of suicide.)
If you suspect that depression has become a problem for you, regardless of its cause, consider doing a consultation with a mental health professional. There are effective treatments for depression. Medication or cognitive-behavioral therapy are especially helpful. If you’d like to discuss whether therapy for depression would make sense for you, please contact us today.
