More people develop allergic reactions to cats than thought, research suggests - even those not specifically allergic to the animals.
Cat allergen particles are sticky
The Imperial College London study of 2,000 people found 25% got breathing problems due to cat allergens.
About 15% of the population is allergic to cats.
But breathlessness was even reported in those without a specific cat allergy, the American Journal of Respiratory and Critical Care Medicine reported.
The study looked for greater bronchial responsiveness - breathing problems similar to an early stage of asthma - as opposed to a full blown allergic reaction which can include runny eyes and skin rashes.
Researchers collected house dust samples from homes of 1,884 people from 20 different areas throughout Europe and analysed them for levels of cat allergen, grass allergen, mould and dust mites.
Blood tests looking for an antibody called IgE - which is a sign of an allergic response - were also carried out.
They revealed one in four of the volunteers, who were picked to be representative of the general population, had at least one allergy.
And the higher the level of cat allergens, the worse the lung function, even among those not allergic to cats.
Lead researcher Susan Chinn said the findings were "surprising".
"We presupposed that we would find increased responsiveness only in those individuals who were exposed to cat allergen and whose blood tests showed that they were allergic to cats.
"But our study suggests that all allergic individuals have signs of asthmatic responses if exposed to cat allergen, even if blood tests show that they are not allergic to cats.
"It appears that many individuals could benefit from reduced cat ownership and exposure."
Muriel Simmons, of the charity Allergy UK, said: "In many ways the findings are to be expected. Cat allergens are extremely sticky, which means they attach to people very easily and can cause the sort of problems reported.
"But I would not say to people they should rush out and get rid of their cats. Our advice is to keep cats out of your bedrooms to try to reduce exposure, but really there is no way to avoid it altogether.
"Even if you don't have cats, you will come into contact with people who do."