For years, parents of children with asthma have faced a painful question: should the family cat stay or go? New research from Sweden suggests the answer may not be as clear-cut as many people feared.

Asthma remains the world's most common chronic disease among children and one of the leading reasons for hospital admissions. According to the Global Asthma Network, around 9.1% of children and 11% of adolescents globally live with the condition. Air pollution, tobacco smoke, obesity, viral infections, eczema and hay fever are known risk factors, but household pets, especially cats, have become a topic of heated controversy.

Now, a large nationwide study published in Frontiers in Allergy offers fresh evidence that living with a cat may not worsen asthma symptoms or outcomes in children already diagnosed with asthma and allergies.

Researchers from Karolinska Institutet in Stockholm followed 30,277 Swedish children aged four to 17 who had asthma or airway allergies. Using data from the Swedish National Patient Register, the Prescribed Drug Register, and the National Airway Register, they tracked emergency visits, medication use, asthma flare-ups, lung function, and disease control over a two-year period ending in 2024.

Among the children studied, 9.4% lived in households with at least one registered cat. Yet researchers found virtually no meaningful difference between children who lived with cats and those who did not.

“Here we show in a nationwide cohort of children in Sweden with asthma and allergies that children living with a cat had similar asthma severity, exacerbation, asthma control, and lung function to children living without cats in the short term,” said corresponding author Dr Resthie R. Putri, a postdoctoral fellow at Karolinska Institutet in Stockholm.

“We also did not see any differences in asthma outcomes related to the number of cats, the cat’s sex, or the cat’s age.”

The findings challenge a widespread belief that cat fur or dander automatically makes asthma worse. Cat dander consists of tiny flakes of skin and proteins that can trigger allergic reactions in sensitive individuals. Many families assume that avoiding cats is essential for asthma control. This study suggests the relationship may be more complicated.

Moderate-to-severe asthma was recorded in 9.6% of children exposed to cats compared with 10.1% among those without cats at home. Asthma attacks, also known as exacerbations or flare-ups, occurred in 3.3% and 3.5%, respectively. Lung function tests, which measure how effectively a person breathes, showed no significant differences either.

Scientists say one explanation may lie beyond the home.

“One possible explanation is that cat allergen exposure is very common, even outside the home. Children who do not have cats at home may still be exposed in shared environments such as schools or public transportation, which could explain why we didn’t see a difference,” said Putri.

Previous studies investigating pet exposure and asthma have produced conflicting results. Many involved small groups of participants or focused only on highly allergic children, making it difficult to draw conclusions for the wider population. The Swedish study stands out because of its scale and the use of national health records, giving researchers a much broader picture of real-world outcomes.

Still, the researchers urge caution.

“While these large-scale findings provide valuable insight, we lacked data on which allergens the children were sensitised to, and because the National Cat Register is relatively new, some children living with cats may have been misclassified as unexposed,” she cautioned.

Experts say the findings should reassure families that owning a cat does not necessarily mean poorer asthma control. However, individual responses vary, and children with confirmed cat allergies may still experience symptoms. For many families, the decision about keeping a beloved pet should be guided by medical advice, careful monitoring, and the child's specific allergy profile rather than just assumptions.