Risk Factors for Schizophrenia: From Family History to Exposure to Toxins

Schizophrenia is a serious mental health condition that causes those living with it to lose touch with reality. The condition is lifelong, but the symptoms can be managed with the right treatments in place.

 

People living with schizophrenia experience many different symptoms, but they usually fall into the following 5 categories:

 

• Psychosis occurs when the brain cannot properly process information, causing your loved one to lose touch with reality. During a psychotic episode, the brain thinks differently than normal, which makes it difficult to understand what’s real and what isn’t. 
• Delusions are beliefs that aren’t true or based on evidence. These beliefs are usually fixed, and the person experiencing them cannot be rationally talked out of them. For example, some people experience religious delusions and become convinced that they are a spiritual figure.
  
• Hallucinations occur when someone has a sensory experience that isn’t real. These can include sights, sounds, tastes, smells, and feelings. Hearing voices and other auditory hallucinations are the most common for many people living with schizophrenia. 
• Disorganized thought and speech patterns refer to jumbled or nonsensical thoughts or conversations. For example, a person experiencing this might jump between topics or respond to a question with an unrelated answer. 
• Disorganized motor patterns are movements that lack purpose or intention. These are often repetitive and out of place, which causes significant problems in daily life.

The exact causes of schizophrenia aren’t well understood. Scientists believe that the individual causes of schizophrenia vary depending on the person. However, there are several factors that are believed to put a person at greater risk for developing schizophrenia. It’s important to understand that even if someone you love has risk factors for schizophrenia, that doesn’t necessarily mean that they will develop the condition.

If you believe that someone you know has a schizophrenia diagnosis, knowing the risk factors can help you develop a better understanding of their condition. Alternatively, if you are concerned that you might be showing signs of schizophrenia yourself, identifying common risk factors is an important part of the diagnostic process.

Let’s take a closer look at the most common risk factors for schizophrenia.

Family plays a significant role in the development of schizophrenia. The genes someone inherits from their biological family are thought to contribute to the development of the condition. The environment that a person’s family creates during their childhood also plays a significant role in whether or not someone will develop schizophrenia.

Schizophrenia and Genetics

Many scientists believe that there is a strong genetic component to schizophrenia. A study published as recently as 2023 suggests that there are specific genes influencing brain development that make a person more susceptible to schizophrenia, as well as other psychiatric conditions. You can think about this as a predisposition—it makes it more likely that someone will get schizophrenia if other risk factors also exist, but it doesn’t guarantee that your loved one will have the condition.

 

Studies have shown that the risk of developing schizophrenia is eight times higher in individuals with one close blood relative who has the condition than it is for someone who doesn’t have a relative with the condition. The likelihood is 11 times higher for people with two close-blood relatives with the condition. This risk factor is the same for people who are raised by their biological family and for people who are adopted. That suggests that the risk is caused by genes, not necessarily by the shared family environment. However, it is important to note that conditions during childhood are also thought to be risk factors for bipolar disorder.

 

Studies conducted on identical twins suggest that if your identical twin has schizophrenia, you have about a 50% chance of developing the condition yourself. This demonstrates that, while genes almost certainly play a role in the development of schizophrenia, they are not the only factor. If they were, twins with virtually identical genetics would have a 100% likelihood of both developing the condition.

 

The above-mentioned studies lead scientists to hypothesize that genes account for as much as 81% of the risk of developing schizophrenia. Other studies suggest that genetics account for somewhere between 60% and 80% of the likelihood of developing schizophrenia.

 

Schizophrenia and Family Environment

The environment a child grows up in has a strong influence on whether or not they develop schizophrenia in their lifetime. Growing up with family members who have schizophrenia often creates stress in the home environment, as well as room for abuse. A 2019 study found that children who experience abuse and neglect in the home during childhood are more likely to develop schizophrenia than those who don’t.

 

This doesn’t mean that every person with schizophrenia was abused as a child—many people with schizophrenia come from loving homes. Schizophrenia has a severe impact on not just the person living with the condition but also their entire family. It is important not to blame well-intentioned parents for the (adult) child’s condition.

A number of environmental factors are also thought to increase the likelihood that a person will develop schizophrenia. Think of them as triggers. While these factors won’t necessarily cause schizophrenia in any one person, they can “activate” the condition in people with predispositions.

Viral Infections and Schizophrenia

There is some evidence that viral infections play a role in the development of schizophrenia. These infections can:

 

• Cause damage in certain parts of the brain
• Change the way certain brain cells act
• Affect neurotransmitters, changing the way the brain communicates
• Lay dormant for years before causing problems.

 

One study suggests that people who are newly diagnosed with schizophrenia often have antibodies for herpes simplex virus (HSV) and cytomegalovirus (CMV), which are both types of herpes. This could mean that something about the way the virus impacts a person with a certain subset of genes leads to the development of schizophrenia.

 

Exposure to Toxins and Schizophrenia

Exposure to toxins during childhood or even prenatal development may play a role in the development of schizophrenia. One study from 2020 found that prenatal and early childhood exposure to lead is more common in people with schizophrenia than in the rest of the population.

 

Lead is commonly found in gasoline, as well as older paints and pipes. In the U.S., an active effort has been made to decrease lead exposure over the last several decades. However, it can still be present in older homes and could affect drinking water if found in pipes and paint used before 1978.

 

There does appear to be a relationship between schizophrenia and substance use disorder (SUD). The relationship between marijuana use and schizophrenia is one of the most highly studied, as both are known to cause psychotic symptoms. One large-scale 2023 study suggests that 30% of schizophrenia cases in young men could have been prevented had cannabis use disorder not developed.

People with schizophrenia are about 30% more likely to have an SUD than the rest of the population. However, the substance use does not always predate the symptoms of schizophrenia. Regardless of which comes first, substance use is often associated with worsening symptoms. If someone you love is managing substance use and schizophrenia, encourage them to seek co-occurring treatment.