What causes depression, and why are some people more vulnerable? Read in plain language how biological, psychological and life factors influence one another.
"He hasn't got a care in the world, so why would he get depressed?" You may have heard this said about someone close to you, or thought it about yourself. Or the opposite: "She's been through so much; how could she not be depressed?" Both sentences rest on the assumption that depression can be explained by a simple cause-and-effect relationship. Yet the reality is more complex and, in fact, more hopeful. The answer to the question of what causes depression lies not in a single cause but at the point where biological, psychological and life factors that influence one another meet. In this article we will explain these factors one by one, show how they come together, and describe why understanding the causes matters in the recovery process.
What Causes Depression? Not Chasing a Single Cause
For many years, attempts were made to explain depression either entirely through "brain chemistry" or entirely through "life's hardships". The approach widely accepted in the mental health field today is the biopsychosocial model. According to this model, depression arises from the interaction of a person's biological make-up, their ways of thinking and regulating emotions, and the conditions they live in.
An easy way to understand this is to imagine a bucket. Some people's buckets are smaller, or already half full, because of their genetic make-up and early experiences. The stresses life brings add water to this bucket: a loss, unemployment, an illness, a long-running conflict. When the bucket overflows, a depressive episode may begin. Someone with a large bucket can also overflow if enough water is added; someone with a small bucket may reach overflowing point with less stress.
This perspective corrects two common misconceptions at once. Depression is not something that happens to "weak people"; under enough strain, anyone can become depressed. Likewise, depression is not impossible for "those without a care in the world"; if vulnerability is high, stresses that look small from the outside can also trigger the picture.
In scientific terms this approach is also called the stress-vulnerability model. This model has an important consequence: because the causes have many layers, the points of intervention have many layers too.
Biological Factors in Depression
Genetic Predisposition
It is a well-known finding that depression is more likely in people with a family history of depression. However, this does not mean there is a single "depression gene". We are talking about a predisposition made up of small contributions from many genes, and this predisposition is not destiny. We have discussed this subject in detail in our article is depression hereditary.
The Brain and the Stress System
You have probably heard the sentence "Depression is a lack of serotonin" many times. This is a considerably simplified version of the truth. In depression, changes are known to occur in the brain's emotion regulation, reward and motivation circuits, in communication between nerve cells, and in the systems that regulate stress hormones. Long-term stress keeps the body's stress response system constantly switched on, and over time this can affect mood, sleep and energy. In other words, biology matters, but it is too complex to be explained by the lack of a single substance.
Hormones and Physical Illness
Hormonal changes such as thyroid disorders, the period after giving birth and the transition into menopause can increase the risk of depression. Long-term health problems such as heart disease, diabetes, chronic pain, neurological diseases and cancer can also pave the way for depression through both biological and psychological routes. The side effects of some medications can affect mood as well; for this reason, assessing physical health is important.
Sleep and the Body Clock
Sleep problems are both a symptom of depression and a factor that triggers it. Working night shifts, sleeping irregularly for long periods and being deprived of daylight disrupt the body clock and can have a negative effect on mood.
Alcohol and Substance Use
Although alcohol and some substances may seem to bring relief in the short term, in the long term they can lower mood, disrupt sleep and contribute both to the onset of depression and to its continuation. A vicious circle often forms: the person drinks because they feel bad, and feels worse the next day because they drank. This relationship runs in both directions and is a subject that should always be discussed in an assessment.
Psychological Factors in Depression
Thinking Habits
According to cognitive theories, in people prone to depression a tendency towards negative thinking stands out in three areas: thoughts about the self ("I'm inadequate"), about the world ("Nobody will help me") and about the future ("Nothing will change"). These thoughts kick in when negative events occur and lead the person to perceive what has happened as heavier, more permanent and more personal than it is. Let us say a project of yours was criticised at work. Thinking "I can't do anything right" instead of "This project was lacking in some places" multiplies the emotional impact of the same event.
Rumination
Thinking over negative events and feelings again and again without reaching a solution plays an important role both in the onset of depression and in its continuation. A mind turning over the questions "Why did this happen, why me, why does it always happen like this?" keeps the person stuck where they are instead of moving them to act.
Early Schemas
Childhood experiences such as emotional neglect, constant criticism, excessively high expectations, losses or abuse can lead a person to develop deep beliefs about themselves and the world. In schema therapy these are called early maladaptive schemas: "I'm defective", "My needs won't be met", "I'm doomed to fail" and so on. When these schemas are triggered in adulthood, they can pave the way for depression. We have discussed the relationship between schemas and psychological resilience in our article on early maladaptive schemas and psychological resilience.
Perfectionism and Self-Criticism
People who set very high standards for themselves and treat themselves harshly when they fail to meet them can be more vulnerable in the face of failure or mistakes. A lack of self-compassion is seen as an important risk factor for depression.
Learned Helplessness
Someone who repeatedly experiences situations in which, whatever they do, they cannot change the outcome may eventually stop trying. This leads to passivity and hopelessness even in circumstances that really could be changed. We have also explained this concept in our article on learned helplessness.
Life and Social Factors in Depression
Depression does not arise in a vacuum but within a life. Some life events and circumstances markedly increase the risk:
- Losses: The death of a loved one, divorce, separation, redundancy, loss of health.
- Ongoing stress: Long-term financial hardship, debt, job insecurity, a heavy caring load.
- Relationship problems: A constantly conflict-ridden marriage, emotional abuse, being devalued within the family.
- Loneliness and social isolation: Having nobody to turn to for support.
- Traumatic experiences: Violence, abuse, accidents, disasters.
- Major life changes: Migration, retirement, becoming a parent for the first time, children leaving home.
In Turkey in recent years, some of these factors have been experienced on a societal scale. The 6 February 2023 earthquakes shook millions of people's homes, loved ones and sense of security about the future. The ongoing worry about making ends meet created by the high cost of living has increased tension in many families. In big cities, long working hours and hours spent in traffic have narrowed the time people devote to rest and to their relationships. In smaller towns, young people being unable to find work and migrating to other cities has created a sense of loss both in those who leave and in those who stay.
Then there are the invisible burdens. In Turkey, many middle-aged adults carry their own children through school and exam processes while also taking on the care of their ageing parents. Hospital appointments, keeping track of medication, phone calls in the night and responsibilities that cannot be shared among siblings create a silent tiredness that lasts for years. Because this burden is usually seen as a "duty", it goes unspoken, but it keeps adding water to the bucket drop by drop.
It is also a well-known finding in the field that depression is more common in women. Behind this, alongside hormonal factors, lie social factors such as most of the caring load at home falling on women, the "double shift" and violence.
Understanding the causes of depression is not about finding someone to blame; it is about seeing where recovery can begin.
What Causes Depression: How Do the Factors Come Together?
Imagine two people made redundant on the same day. One feels down for a few weeks and then starts looking for a new job; their spouse and friends are by their side, and financially they can manage for a few months. The other has lived with the belief "I'm inadequate" since childhood, has a family history of depression, is behind with the rent and cannot tell anyone about their troubles. In the second person, the likelihood of developing depression is much higher. The event is the same, but the buckets are different.
This example shows that the factors work in three different roles:
- Predisposing factors: Long-term factors that make a person more open to depression, such as genetic make-up, early experiences and schemas.
- Precipitating factors: The events or circumstances that start the depressive episode.
- Perpetuating factors: Factors that contribute to depression continuing, such as avoidance, rumination, withdrawal, sleep disturbance and alcohol use.
Protective factors must be added to these: strong social support, problem-solving skills, self-compassion, a meaningful occupation, a regular rhythm of life and seeking help early. Protective factors are like taps that drain some of the water when the bucket is close to overflowing.
This distinction turns the question of what causes depression into a practical one: setting aside what cannot be changed (genetic make-up, the past), what can we change right now? Most perpetuating factors are areas that can be worked on directly in therapy.
When Should You Seek Professional Support?
Knowing exactly what caused your depression is not a precondition for seeking support. We recommend that you contact a mental health professional in the following situations:
- If low mood or loss of pleasure has continued for more than two weeks
- If there are marked changes in your sleep, appetite, energy and attention levels
- If you cannot recover after a loss or a stress you have experienced
- If there is a history of depression or other mental health problems in your family and you are noticing similar symptoms
- If you are struggling to keep up with your daily tasks, your work or your relationships
If you have thoughts of harming yourself or ending your life, be sure to share them with a professional. In an emergency, call 112 (emergency services) or go to the nearest emergency department.
A medical assessment to understand whether the symptoms are related to a physical cause and, in moderate and severe cases, an assessment by a psychiatrist are also part of the process.
How Are the Causes of Depression Addressed in Therapy?
In therapy, causes are examined not to find someone to blame but to draw up a map specific to the person. This map is called a case formulation. The professional and the client look together for answers to these questions: What might make you vulnerable to depression? What started this episode? What is currently contributing to the depression continuing? What strengths and sources of support do you have?
Cognitive Behavioural Therapy (CBT) focuses especially on perpetuating factors: negative automatic thoughts, rumination, avoidance and withdrawal. These cycles are noticed and changed step by step. Activities that bring meaning and pleasure back into the person's life are planned.
If predisposing factors are to the fore, that is, if the depression is fed by deep beliefs that have lasted for years, schema therapy helps to understand how these beliefs were shaped in childhood and to transform them. If relationship problems are an important trigger, relationship patterns and communication skills are worked on. For ongoing sources of stress, problem-solving and boundary-setting skills are developed.
In individual therapy, this map becomes clearer over time, and as the person understands how their own depression works, they can take more effective steps against it. Understanding the causes also makes it easier to spot high-risk periods in advance in the future.
Frequently Asked Questions
Can depression happen for no reason at all?
Depression can arise even when no clear trigger is visible from the outside. In this case, biological predisposition, accumulated small stresses, changes in sleep and the body clock, or unrecognised emotional burdens usually play a role. The fact that it seems to have "no reason" does not mean the picture is not real.
Is depression a weakness of character?
No. Depression is a health problem that arises from the interaction of biological, psychological and social factors. Under enough strain, anyone can become depressed. Seeing depression as weakness delays people from asking for help.
Do childhood experiences lead to depression in adulthood?
Childhood experiences such as emotional neglect, constant criticism, losses or abuse can increase the risk of depression in adulthood. However, this is not destiny; supportive relationships and therapy help to understand and transform the impact of these experiences.
Can I be treated without knowing the cause of my depression?
Yes. Many people do not clearly know the cause of their depression when they start treatment; this does not prevent the treatment from being effective. The causes tend to become clearer over time during the therapy process anyway. What matters is that the symptoms are assessed and a treatment plan suited to you is drawn up.
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Eda Erkan Alapala
Klinik Psikolog. İstanbul Kent Üniversitesi Klinik Psikoloji Tezli Yüksek Lisans mezunu; bilişsel davranışçı terapi, çocuk merkezli oyun terapisi ve çocuk-ergen psikoterapisi alanlarında eğitimlerini tamamlamıştır.
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