Causes and Risk Factors

Experts do not know the exact cause of schizophrenia, a serious mental health condition. However, a combination of different factors is the most likely cause. Some possible causes of schizophrenia are related to genetics, brain development, stress, and the balance of chemicals in the body. Socioeconomics, experiences, and lifestyle are also linked to the development of schizophrenia.^1-5

Genetics

You inherit genes from your parents. These genes determine many things about you. There are genes for eye color, height, and more. Beyond how you look, your genes determine how your body functions. Changes in genes (called mutations) can lead to different health conditions.⁶

Research on twins or families is helpful in learning whether a health issue is genetic. Twin studies looking at schizophrenia have led to interesting results. Experts have found that if a person with schizophrenia has an identical twin sibling, there is a nearly 50 percent chance that their twin has schizophrenia, too. If they have a nonidentical twin sibling, there is around a 10 percent chance that their twin has schizophrenia.^1,2

These numbers are much higher than what we would expect for 2 people at random across the world. This means that genetics likely is part of having schizophrenia.³

However, identical twins have the same genes. So, if schizophrenia were completely genetic, the identical twin of someone with schizophrenia would nearly always have it too. Since this is not the case, there are also environmental factors at play as well.³

Brain development and chemical balance

It is almost guaranteed that people with schizophrenia have structural changes to certain areas of their brain. Some areas may be different sizes or have different activity than usual. These changes affect the way the brain functions or sends messages.^1,3-5

Cells in the brain use chemicals to send messages to one another. These are called neurotransmitters. Examples of neurotransmitters are dopamine and glutamate. Experts have discovered that drugs that impact dopamine and serotonin levels help improve schizophrenia symptoms. These drugs are called antipsychotic drugs. Their effect on symptoms has led to a theory that schizophrenia is related to changes in neurotransmitter balance.^1,3-5

Pregnancy or birth-related issues

Changes in brain development may have started even before a person was born. Babies in the womb (in utero) can be affected by things happening to the pregnant parent. If this parent has diabetes, poor nutrition, or an infection during pregnancy, the baby may be impacted. All of these issues can affect a baby’s growth and development.^1-5,7

Events during birth may also have an impact on a baby’s brain and body development. Things like early (pre-term) birth, low oxygen around the time of birth, or blood loss during birth can also play a role. Birth and pregnancy-related issues can increase the risk for schizophrenia later in life.^1-5,7

It is important to note that all of these issues are common. Not every baby who experiences one of these issues will develop schizophrenia. They are simply factors that can increase risk or affect the way the brain works later in life.²

High levels of stress

Stress can come in many forms. It may result from childhood trauma, neglect, unstable housing, financial trouble, or social isolation. Stress that does not have appropriate relief or coping strategies leads to changes in hormone balance. This affects the way the body and brain function.^8-10

Certain infections and health conditions can also expose your body to stress. This strain on the body may act as a trigger for schizophrenia symptoms. While they do not know the exact connection, many experts believe that significant, long-term stress can play a role in developing the condition.^1,3,7-9

Substance use

Using certain recreational drugs, like marijuana (cannabis), cocaine, or acid (LSD), may increase the risk of developing schizophrenia. Cigarette smoking may also play a role.^1,3,7

It is unclear which factor may lead to the other, though. It could be that these drugs affect the brain and lead to schizophrenia symptoms. But it is also possible that people who are likely to develop schizophrenia have a higher risk of developing substance abuse. More research is needed to understand the potential connection between the two.^1,3,7

Risk factors for schizophrenia

There are certain factors that increase a person’s risk of developing schizophrenia. Some of these factors are linked directly to possible causes. For example, having a close family member with schizophrenia may point to a genetic cause.³

Other examples of risk factors for schizophrenia include:^1-5,7-10

• Experiencing trauma or neglect during childhood
• Growing up in an urban or city environment
• Having lower income
• Facing major social challenges like an unstable home life, discrimination or isolation, or limited social support
• Issues during your birth, like having low oxygen levels
• Complications during your birth parent’s pregnancy, like infection
• Being born during the late winter or early fall (especially during years with a flu pandemic)
• Heavy marijuana use, especially during teenage years
• Smoking cigarettes or using other drugs

This is not a complete list of all the risk factors for schizophrenia. If you are concerned about your or a loved one’s risk, talk with your doctor.