Cats are among the world’s most popular pets, but a recent scientific review has reignited debate about whether exposure to cats could be linked to a higher risk of schizophrenia-related disorders. Researchers stress that the findings do not prove cats cause mental illness, but they do suggest an association that deserves further investigation.
The review, led by scientists at the Queensland Centre for Mental Health Research in Australia, analyzed more than four decades of research and found a modest but recurring connection between cat exposure and schizophrenia spectrum disorders, particularly when exposure occurred during childhood.
What The Review Found
The research team, led by psychiatrist John McGrath, examined 17 studies conducted across 11 countries over a 44-year period. After pooling the data, they found that individuals exposed to cats had roughly twice the odds of developing schizophrenia-related conditions compared with those who had not been exposed.
Most of the studies used a case-control design, comparing people diagnosed with schizophrenia or related disorders to individuals without these conditions. While many studies reported a positive association, others found no significant link, and some suggested that the timing of exposure during childhood may be especially important.
One study found no overall connection between cat ownership before age 13 and later schizophrenia risk. However, when researchers looked specifically at cat ownership between ages 9 and 12, a significant association emerged, highlighting ongoing uncertainty about when exposure may matter most.
The Toxoplasma Connection
One of the leading theories involves Toxoplasma gondii, a parasite commonly associated with cats. Humans can become infected through contact with contaminated cat feces, undercooked meat, or contaminated water. Once infected, the parasite can remain in the body for years, including within the brain.
T. gondii infection is extremely common. According to the U.S. Centers for Disease Control and Prevention, more than 40 million Americans may carry the parasite, often without knowing it. Some research suggests the parasite may influence neurotransmitter activity, alter behavior, and potentially contribute to psychiatric symptoms.
Several studies have reported higher rates of T. gondii antibodies among people with schizophrenia than in the general population. However, researchers emphasize that these findings show correlation rather than causation and do not prove that cats are responsible for the increased risk.
Could Other Factors Be Involved?
Not all evidence points directly to cats or T. gondii. In one study involving 354 psychology students in the United States, cat ownership itself was not associated with higher levels of schizotypy, a collection of personality traits linked to psychosis risk.
Interestingly, participants who reported being bitten by a cat scored higher on schizotypy measures than those who had never been bitten. Similar findings have been reported elsewhere, raising the possibility that other microorganisms carried by cats could be involved.
Researchers have suggested that bacteria such as Pasteurella multocida, commonly found in cats’ mouths, might contribute to some of the observed associations. Environmental influences, family factors, or shared genetic traits could also help explain why certain patterns appear in the data.
Important Limitations
Mental health experts caution that the current evidence remains far from conclusive. Fifteen of the 17 studies included in the review were case-control studies, which can identify associations but cannot determine cause and effect.
Many studies also relied on participants recalling details about childhood pet ownership many years later, which introduces the possibility of recall bias. In addition, differences in culture, pet-keeping habits, and research methods make comparisons across countries difficult.
When researchers adjusted more carefully for potential confounding factors, some associations became weaker, suggesting that other influences may be contributing to the findings.
What Cat Owners Should Know
Experts stress that there is no reason for cat owners to panic or give up their pets. Schizophrenia is a complex disorder influenced by genetics, brain development, environmental stressors, and biological factors. No single cause has been identified.
For most healthy people, T. gondii infection causes few or no symptoms. Simple hygiene practices, such as washing hands after handling litter and cleaning litter boxes regularly, can greatly reduce the risk of infection. Pregnant individuals and people with weakened immune systems are generally advised to take extra precautions.
The authors of the review argue that cat ownership should be viewed as one of many possible risk-modifying factors rather than a direct cause of mental illness. They call for large, long-term studies that track pet exposure, infections, genetics, and mental health outcomes over time.
What Happens Next?
Future research will aim to clarify whether parasites, bacteria, environmental influences, or a combination of factors are responsible for the observed associations. Scientists are particularly interested in understanding how infections and immune system activity may interact with brain development and psychiatric disorders.
For now, the evidence suggests caution rather than alarm. While researchers continue to investigate the relationship between cat exposure and schizophrenia, experts agree that responsible pet ownership and good hygiene remain the most practical approach.
The review was published in Schizophrenia Bulletin and has renewed scientific interest in how infections, immunity, and environmental exposures may contribute to serious mental illnesses.
