The causes of schizophrenia are not yet fully understood. Researchers do not yet know exactly what causes some people to develop schizophrenia. There is a very strong genetic component to schizophrenia. However, genes alone do not completely explain the illness.
Most scientists believe that genes don’t cause schizophrenia directly but do make a person vulnerable to developing the disorder. Scientists are studying many possible factors that might cause a person with a genetic predisposition to develop schizophrenia.
At a Glance
While schizophrenia is believed to have a strong genetic component, inheritence alone does not provide a full explanation for who develops this condition and who doesn’t. Instead, experts believe that it is a complex interplay of factors that play a part. Genetics, environment, lifestyle, family history, and social influences have all been implicated. Keep reading to learn more about the causes of schizophrenia and some of the factors that can elevate the risk of developing this condition.
Verywell / Cindy Chung
What Is Schizophrenia?
Schizophrenia is an illness of the brain that causes certain characteristic symptoms, abnormal experiences, and behaviors. For different people, schizophrenia can involve different clusters of symptoms. It is possible that slightly different disease processes are involved in these different clusters.
However, many researchers believe that schizophrenia is a single disease that can have different effects depending on which brain regions are most affected. In the latest edition of the DSM, the subtypes of schizophrenia were removed.
Family History and Genetics
There is strong evidence of a genetic role in schizophrenia. In the general population, schizophrenia occurs in slightly less than 1% of people. However, having a family member with schizophrenia can significantly increase your risk of developing the condition.
Family Connections
Genetic predisposition influences whether someone will develop symptoms of schizophrenia, as seen in other medical and mental health conditions. Older research supports this with findings such as:
- If your brother or sister or one parent has the illness, your chance of having schizophrenia is around 10%.
- If one parent has the condition, it raises your chances of developing schizophrenia by about 13%.
- If your identical twin has the illness, you have a roughly 50% chance of developing schizophrenia.
- If both of your parents have schizophrenia, you have a 40% likelihood of developing the illness.
One 2020 meta-analysis found that people with a close relative with schizophrenia have a seven to eight times higher risk of developing the condition compared to people who don’t share a close connection. Chances were even higher for those with two close relatives with the condition, making them around 11 times more likely to develop schizophrenia during their lifetime.
We know these family risks are due to genetics rather than family environment, as these rates are the same whether a person is raised in the birth family or not. The children of people with schizophrenia are more frequently given up for adoption because their parents are too ill to care for them.
However, genes alone don’t cause schizophrenia. If they did, then identical twins, who share virtually the same genetic code, would have closer to 100% risk for developing the condition.
Twin studies suggest that genetics account for 81% of the risk for schizophrenia. Other studies estimate that the heritability of schizophrenia is around 60% to 80%.
Environment
Certain environmental factors can also contribute to the development of schizophrenia. Twin studies suggest that shared genetic environments account for 11% of the risk. Environmental risk factors may include:
Viral Infections
Exposure to viruses is found to contribute to the development of schizophrenia. Viruses may contribute in several ways, such as:
- Attack certain brain regions and leave others intact
- Alter certain processes within a brain cell without killing the cell
- Infect someone and then lay dormant for many years before causing illness
- Cause minor physical abnormalities, birth complications, and altered fingerprint patterns sometimes found in people with schizophrenia
- Affect neurotransmitters
It is also important to note that some antipsychotic agents are also antiviral agents, which can also support the idea that viral infections can play a role in the development of schizophrenic symptoms, particularly psychotic symptoms.
Herpes Viruses
People who have recently developed schizophrenia very often have antibodies to two herpes viruses in their blood, HSV (herpes simplex virus) and CMV (cytomegalovirus). Studies suggest that when certain viruses infect someone with a particular set of genes, that person is more likely to develop schizophrenia.
Other Infectious Influences
People with schizophrenia also are more likely to show antibodies to toxoplasmosis gondii, a parasite carried by cats that can also infect humans. Although the data is mixed, some studies have suggested being raised around cats slightly raises a person’s likelihood of developing schizophrenia and that the illness is more common in countries and states where many people have cats as pets.
Infectious disease theories of schizophrenia are very exciting and promising. It is too early to know if researching these theories will reveal a major cause of schizophrenia, but further study will go a long way toward informing future diagnosis and treatment of the condition.
Exposure to Toxins
Being exposed to harmful toxins are suggested to play a role in the development of schizophrenia, even as early as during fetal development. Toxins that have been researched to show possible influence include alcohol and lead.
Lead
Lead exposure has also been implicated as one of the causes of schizophrenia. Exposure to lead during fetal develop has been shown to significantly influence the likelihood of the development of schizophrenia and psychosis. Lead can be found in things such as:
- Gasoline
- Paint
- Tap water
- Children’s toys
Although measures have been taken in recent years to remove lead from the things we come in contact with every day, it is important to be aware that lead can still be in our environment. If a home was painted with lead paint before 1978, it can still release this toxin.
Societal Factors
Because the causes of schizophrenia have been so difficult to define, much research has been devoted to investigating societal issues that could potentially contribute to the onset of the disorder in some people. Some of the potential social causes of schizophrenia include the following factors:
Living in a Populated Area
It has been suggested that living in a densely populated area can be a risk factor in the development of schizophrenia. Research has shown that people who grew up in metropolitan areas were more likely to be diagnosed with schizophrenia than those who lived in the country or rural areas.
Prenatal Exposure to Hunger
The children of women experiencing famine during the first three months of their pregnancy have been shown to be more likely to develop schizophrenia.
Family Environment
Being raised in a family with schizophrenia greatly increases the stress and likelihood of abuse and trauma, and children from these homes are more likely to develop the illness themselves. Exposure to stress in childhood may trigger the onset of the condition in people with a genetic predisposition to the condition.
It is certainly possible to look in the history of many people with schizophrenia and find past trauma, but many more people with schizophrenia came from loving, supporting homes. One of the many tragedies of schizophrenia is that well-meaning people often assign blame to parents already heartbroken by the illness of their beloved child.
It is important to realize that these risk factors do not, in themselves, indicate a cause of schizophrenia. Instead, scientists are looking for underlying differences among these groups of people that can explain why they experience different levels of risk.
Brain and Body Risk Factors
Developmental theories of schizophrenia suggest that something goes wrong when the brain is developing. Brain development, from the earliest stage of fetal development, the early years of life and through adolescence, is an extremely complicated process. Millions of neurons are formed, migrate to different regions of the forming brain, and specialize to perform different functions.
The “something” that goes wrong might be a viral infection, a hormonal imbalance, an error in genetic encoding, a nutritional stress, or something else. The common element in all developmental theories is that the causal event occurs during the brain’s development.
Even though these potential causes may be rooted in very early development, symptoms of schizophrenia typically emerge in late adolescence or early adulthood.
Early Disruptions
Developmental theories suggest an early disruption causes the brain structure to be disorganized. The start of puberty brings a number of neurological events, including the programmed death of many brain cells, and at that time the abnormalities become critical.
Developmental theories suggest there are a number of risk factors for schizophrenia related to critical periods in fetal development, such as:
- Schizophrenia is more common in winter and spring births.
- Children whose mothers experienced famine during the first trimester are more likely to develop schizophrenia.
- Pregnancy and birth complications increase the risk of developing schizophrenia.
However, there is not yet enough evidence that the brains of adults with schizophrenia are disorganized in the ways that developmental theories predict. Also, these theories address the when of schizophrenia’s origin, but not the cause itself.
Neurochemicals
Schizophrenia clearly involves irregularities in the chemicals of the brain (neurochemicals) that allow brain cells to communicate with each other.
We know this because influencing certain neurotransmitters with drugs (like amphetamine or PCP) can cause schizophrenia-like symptoms. Also, antipsychotic medications that block the action of the neurotransmitter dopamine can effectively reduce symptoms.
In fact, dopamine imbalance was once thought to be a cause schizophrenia. However, some newer agents (second-generation antipsychotics), such as Abilify (aripiprazole), Rexulti (brezipiprazole), and Vraylar (cariprazine), work without blocking dopamine.
There are also drugs being developed that may not target dopamine receptor antagonism. Current research indicates that abnormalities in the neurotransmitters GABA and glutamate are involved in the cause of schizophrenia.
The difficulty of neurochemical theories is that most brain processes can affect neurotransmitter levels, and neurotransmitters (of which there are at least 100) all interact with one another.
When we say that one particular neurotransmitter or another is causing schizophrenia, we are basing that claim on a single frame of a very long and complicated motion picture without being able to see the frames that led up to the change we’re observing.
The medical treatment of schizophrenia today relies almost entirely upon regulating levels of neurotransmitters, and so research in this area is vital to developing more effective treatments.
Lifestyle Factors
While certain lifestyle factors may seem to be associated with schizophrenia, the connections are more correlational than causal.
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Stress
Psychological stress has physiological effects and is implicated in causing or contributing to psychiatric disorders, including post-traumatic stress disorder. Psychological stress also aggravates disorders like high blood pressure and heart disease.
Certain types of psychological stress, namely traumas in the aftermath of war, natural disaster, or concentration camp imprisonment, have not been shown to cause schizophrenia.
This statement doesn’t make sense to many people familiar with schizophrenia. How can it be true? For one thing, schizophrenia does not become more common after these types of traumas.
However, some research does show an increased risk of developing schizophrenia for individuals who experience traumatic stress disorders, especially if triggering incidents occurred early on in life and/or repeatedly, as in cases of sexual abuse.
Stress also plays a significant role in the control of the illness. People with schizophrenia become very sensitive to stress and change. Psychological stress alone can be enough to trigger an episode. Developing and maintaining a routine is one of the most important aspects of avoiding relapse.
Life-Changing Events
People’s lives are often filled with loss during the time leading up to a first psychotic episode. However, those losses (like relationships, jobs, school, accidents, etc.) are often the result of early-onset symptoms, including suspicion, memory disturbance, withdrawal, and loss of motivation.
Essentially, previously undiagnosed schizophrenia can be the cause of many life-changing events and not the other way around.
Keep in Mind
The causes of schizophrenia are thought to be heavily tied to genetics, but it is important to remember that other factors also play a role. Having a close relative might increase your risk of developing this condition, but it is not a guarantee that you will have schizophrenia.
Being aware of the early symptoms of the condition can help you stay alert and ensure that you seek treatment as soon as possible, which can lead to better outcomes and help improve the course of the illness. If you suspect that you or a loved one are experiencing symptoms of schizophrenia, talk to your doctor for further evaluation and treatment.
