A complex interaction between your biology, psychology, and social environment may contribute to depression.

If you or someone close to you lives with depression, you may want to learn more about its causes and risk factors.

Decades of research suggest that a complex blend of factors cause depression. Experts have identified many of these factors, as well as factors that could increase your chances of having depression.

For instance, women tend to have higher rates of depression than men. Compared with men, women may be two times as likely to have depression.

The biopsychosocial model is one popular theory for what causes depression. In this model, depression is thought to be caused by a combination of biological, psychological, and social factors.

Major depressive disorder (MDD) is the official term for depression. In this article, we’ll refer to MDD as “depression.”

Researchers have many different models and theories about what causes depression in the brain.

Studies have shown that the brains of people with depression often look different from brains of people who don’t live with depression. Still, it’s unclear in many of these cases whether depression is a result of these brain differences or whether it’s causing them.

The way your brain processes emotion may contribute to depression. Research suggests a connection between depression and reduced activity in parts of the prefrontal cortex. The prefrontal cortex is responsible for reward processing and motivation, among other things.

Depression is linked to reduced reward processing activity in the brain, and studies have connected a dulled response to reward with depression later in life.

Depression’s connection to reward processing may impact the way you feel when you participate in an activity you enjoy. This could be why anhedonia, or loss of pleasure, is a common symptom of depression.

Researchers are still working toward a more complete understanding how of depression impacts the brain. Future research will continue to fill in these gaps.

If you have a depressive disorder, a combination of genetic, psychological, and environmental factors are likely involved. One popular theory suggests that different sets of genes interact with your environment to cause depression.

It’s common for depression to begin in your teen years. Depression is often a long-lasting condition, with an estimated 60% of people who have depression experiencing multiple episodes over time.

Factors that may interact to cause depression include:

  • certain gene sets
  • personality traits
  • significant life events
  • stress and trauma
  • seasonal changes
  • underlying medical issues
  • substance use or medications

Taking steps to address early signs of depression may help you reduce its severity later on. Even if you’ve been living with depression for years, many treatment options can help you manage your symptoms.

Genetics

Some types of depression run in families, suggesting it can be inherited. Research indicates that you’re more likely to have depression if you have a family history of anxiety or depression.

In addition, you may be up to three times as likely to experience depression if one of your parents has it. In this case, your genetic makeup and your parents’ childrearing styles may both play a role in the development of depression.

Epigenetics, or the process by which outside factors act on certain genes, is also connected to depression. For example, stress has been shown to contribute to depression by altering the expression of certain genes.

Despite the strong link between depression and genetics, people with no family history of depression may still experience it. Whether inherited or not, depression is often associated with changes in brain structure and function.

Grief and loss

While grief and depression are two separate things, grief can sometimes lead to depression. Grief may be more likely to lead to depression if you’re already prone to depression or have experienced it before.

Research has linked serious losses that lead to grief or trauma with depression. You may be especially prone to experiencing depression if the loss happened early in your life.

While grief is a natural response to loss, depression doesn’t always have a clear cause. This can make managing symptoms more complicated, but there are still many effective treatment options.

Medical conditions

Depression is closely connected with certain physical symptoms and medical conditions.

The Diagnostic and Statistical Manual of Mental Disorders (DSM-5) reports that the following medical conditions can cause depression:

  • stroke
  • heart attack
  • cancer
  • Parkinson’s disease
  • hormonal disorders

Depression as a medical symptom may increase feelings of apathy, making it harder to care for yourself through your medical condition.

Other research points to the overlooked importance of the gut’s microbiome — the types and amounts of important bacteria that live in your digestive system. The health or imbalance of certain bacteria may contribute to or even cause mental health conditions like depression.

Seasonal changes

In some cases, you may experience depression that is triggered by seasonal changes. This kind of depression is called major depressive disorder (MDD) with seasonal pattern, formerly known as seasonal affective disorder.

If you live with this condition, your depression symptoms are triggered by seasonal changes. While many people experience this during the cold, dark months of winter, it’s possible for it to occur in any season.

Stress

Stress comes in a variety of forms, many of which can trigger depression. In particular, chronic stress — stress that persists for a long period of time — is linked to depression.

Life circumstances that can cause chronic stress include:

  • a difficult long-term relationship
  • financial problems
  • childhood neglect
  • a traumatic experience
  • short or long-term abuse

When you’re stressed, your body releases stress hormones. In cases where stress is chronic, these stress hormones may alter your brain chemistry in a way that causes depression.

Some risk factors may estimate how likely you are to develop depression. Unlike depression causes, risk factors don’t necessarily trigger depression — but their existence may signal that you’re more or less likely to experience depression.

Some common risk factors for depression can include:

  • certain personality traits, such as pessimism
  • age
  • ethnicity
  • co-occurring mental health conditions
  • substance use

It’s not always clear whether risk factors mean you’re prone to depression or whether they’re an early form of depression itself.

Personality traits

Certain personality traits have been strongly connected to your chances of having depression, according to the DSM-5 and other research.

You might be more likely to experience depression if you:

It’s also possible to have any of these traits and not experience depression. But if you have one or more of these traits, you might be more likely to develop depression than someone who doesn’t have any.

Age

Age is an important risk factor when it comes to depression.

It’s common for depression to start showing up during adolescence. The National Institute of Mental Health (NIMH) reports that young adults from 18 to 25 years of age had the highest rates of depression at 13.1% of U.S. adults in 2017.

According to the same data, middle-aged adults (26 to 49 years of age) had the next highest rates of depression, followed by adults over 50 years of age.

Ethnicity

Ethnicity may also indicate whether you’re more or less likely to be living with depression. According to NIMH, adults who reported two or more races had much higher rates of depression compared with other study participants.

Groups who self-identified as white or American Indian/Alaskan Native had the next highest rates of depression compared with the rest of the population.

Since this information is mostly self-reported, more research is needed to address any gaps or biases that currently exist in self-reporting.

Co-occurring mental health conditions

If you have another mental health condition, you may also be more likely to have a depressive disorder. According to the DSM-5, some mental health conditions that tend to co-occur with depression include:

In some cases, one of these conditions could be misdiagnosed as depression, though it’s also possible to have both.

If you have depression and a co-occurring mental health condition, exploring potential causes and risk factors for the second condition may help you better understand your symptoms.

Substance use

It’s still unclear whether depression leads to substance use or substance use triggers depression. The truth is likely that it can go both ways.

Research has repeatedly linked depression to alcohol consumption, for example. One study found that college students with depression were more likely to report increased alcohol use.

Another study found that in older adults, excessive alcohol consumption led to an increase in depressive episodes.

Even if you’re not sure what’s causing your depression, a whole host of treatment options are within your grasp.

Treatment for depression may depend on what type of depression you’re experiencing. It can include talk therapy, medication, lifestyle changes, and home remedies. Learn more about depression treatment here.

It can feel difficult to cope with depression symptoms when those same symptoms sap your motivation and energy. But even small, manageable steps can get you on the path to thriving through depression.