Schizophrenia is a complex illness that can evolve in different ways over time. Researchers have not identified a single cause that explains or is present in all people with schizophrenia.

Scientists think a complex interaction between genetics, early development, environment, and biological factors causes schizophrenia. People are more likely to develop the condition if a parent or sibling has the disease.

Research also suggests that certain diseases and negative life experiences may be risk factors for schizophrenia. Despite this, they do not know the exact role these environmental factors play.

Read on to learn more about the different potential causes of schizophrenia.

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Schizophrenia does not have a single cause. Instead, several risk factors appear to increase the likelihood of a person developing the disease.

Doctors do not yet fully understand how these risk factors interact. It is also unclear why some people with many risk factors do not get schizophrenia while others with few or no risk factors do. Both genetics and environmental factors likely play a role.

Numerous studies have found that genetics play a significant role in the development of schizophrenia. Doctors have not identified a single gene or group of genes that explains all cases of the condition. However, they have found that having an immediate relative with schizophrenia greatly increases the risk.

According to a 2020 paper, a person has a 40% likelihood of developing schizophrenia if both biological parents have it.

When looking at twins, researchers found that if one identical twin has schizophrenia, there is a 46% chance the other will also have it. Identical twins share the same genes, meaning that while there is a strong genetic component to schizophrenia, other factors must play a role.

A large Danish study of 31,524 pairs of twins suggests that schizophrenia has a heritability rate of 79%. Heritability measures how genes explain the difference in symptoms. This heritability rate means that 79% of the differences between people with and without schizophrenia are because of genetics.

Epigenetics is the study of how various triggers, including environmental exposures, such as life experiences or infections, change the behavior of genes.

Epigenetic factors likely play an important role in schizophrenia. In genetically vulnerable people, environmental factors may increase the risk and trigger schizophrenia.

Some environmental factors that may increase the risk include:

  • Maternal behavior and health: A birthing parent’s health during pregnancy may affect the infant’s development, increasing the risk of schizophrenia. Childbirth complications, infections, and conditions, such as preeclampsia, may play a role in the condition.
  • Family environment: The place where a person lives and grows up may increase the likelihood of schizophrenia. People living in urban areas are more vulnerable.
  • Early trauma: Childhood trauma, such as abuse, unstable home life, living in poverty, or exposure to racism, can increase the risk.
  • Substance misuse: Substance misuse may trigger brain changes that increase the risk of schizophrenia. Research has found an especially robust correlation between cannabis use and the condition.
  • Infections: Exposure to certain infections, either when developing during pregnancy or later in life, may be a trigger for schizophrenia. For example, individuals with a history of toxoplasmosis have higher rates of psychosis and schizophrenia.

Many different risk factors increase the likelihood of developing schizophrenia. They include:

  • complications during birth
  • malnourishment in a person’s birth parent
  • being born in winter
  • a family history of schizophrenia
  • using cannabis
  • living in an urban area
  • a birthing parent having the flu during pregnancy
  • childhood trauma such as poverty or abuse
  • social isolation
  • exposure to certain infections, such as toxoplasmosis

Race may also be a risk factor for schizophrenia. Although the direct cause is unclear, health experts believe exposure to racial bias in healthcare may contribute.

However, some research also suggests that doctors overdiagnose schizophrenia in Black individuals.

For example, a 2018 study found that doctors were more likely to disregard mood symptoms of depression and diagnose schizophrenia in Black patients. This means that doctors may misdiagnose psychosis or improperly label other diagnoses as schizophrenia.

No blood or lab test can diagnose schizophrenia. However, a doctor may recommend certain tests to rule out other potential causes of schizophrenia symptoms.

An MRI scan can help rule out a traumatic brain injury, while HIV and syphilis testing can determine whether an infectious disease has damaged the brain. If no other cause explains the symptoms, a doctor may diagnose the condition according to a person’s symptoms.

The Diagnostic and Statistical Manual of Mental Disorders, 5th edition, text revision, requires that a person must have two or more of the following for a diagnosis:

The symptoms must be present for at least 1 month, affect daily functioning, and be unexplainable by another diagnosis.

A person can contact a doctor if:

  • loved ones have expressed concerns about their mental health or worry they may have schizophrenia
  • they see or hear things others do not
  • they experience significant difficulties with daily functions, such as keeping a job
  • they have concerns that they may have schizophrenia symptoms

Schizophrenia is not contagious, but it tends to cluster together in families. Moreover, some contagious illnesses may elevate the risk of the diagnosis or mimic schizophrenia symptoms.

Researchers have not identified a single cause of the condition. Instead, interactions between many different factors may help explain the development of schizophrenia.