Feline effect on asthma

The effect of cats on asthma risk is complex

Having a cat protects at-risk children against asthma - unless their mother is asthmatic, researchers have found.

Previous studies have painted a very confusing picture about whether having a cat in the house protected a child or increased their risk of developing asthma.

But US researchers say their latest findings show the situation is even more complicated that the earlier studies suggested.

They followed 448 children with a family history of allergic diseases from their birth until they were five years old.

It appears that for a vast majority of children, being exposed to a cat early in life may be beneficial

Dr Juan Celedón, Brigham and Women's Hospital

Through regular phone calls, they established if the families had pets and how often the children experienced episodes of wheezing.

Dust samples from each child's home were also tested for levels of cat allergens.

Children with a cat in the house were 40% less likely to experience persistent wheezing compared to those with no exposure to cats.

But this only held true if their mothers were not asthmatic.

This risk reduction remained consistent for each of the five years they were studied.

However the opposite was true for children with cats whose mothers were asthmatic.

In that group, the risk of developing a persistent wheeze, an initial sign of asthma, was double that of those not exposed to cats.

By the age of five, their risk had more than tripled.

Complex disease

Researchers say this could be because they are more sensitive to cat allergens, the first step in developing asthma, and wheeze when exposed to it.

They say this could be due to genetic influences passed on from the mother, or because of environmental influences shared by the mother and child.

The researchers plan to follow the children until they are teenagers to see if the protective effects continue.

Dr Juan Celedón, who carried out the research at Brigham and Women's Hospital in Boston, Massachusetts, said: "This study is the first to show that the effect of having a cat in the home may depend upon whether your mother has asthma or not."

He added: "For years, physicians have been advising families with allergies to stay away from pets.

"However, it appears that for a vast majority of children, being exposed to a cat early in life may be beneficial.

"That said, there is a subgroup of children -- those whose mothers have asthma and, perhaps, those whose mothers are allergic to cats - who should probably avoid cat exposure."

Dr Michael Plaut, head of the allergic mechanisms section at the National Institute of Allergy and Infectious Diseases, said: "Asthma is a complex disease in which there appear to be many factors, both genetic and environmental.

"To better understand asthma, we need studies like this one that sort out these factors and define the relationships among them."

Reducing reaction

A spokeswoman for the National Asthma Campaign told BBC News Online: "This study adds more information to the debate about whether exposure to pets in the early years of life is good or bad and it demonstrates that the story is still very complicated.

"What is becoming clear is that what a child is exposed to in the first years of life and the development of their immune system, could be key to whether they subsequently develop asthma and allergy later in childhood."

A spokeswoman for the Cats Protection League said the findings were good news for most people worried about childhood asthma.

She added: "Even if a member of the household has asthma, there are still many measures people can take to reduce asthmatic reactions."

Special vacuum cleaners, treatments for a cat's coat and restricting what areas of a house a cat can go in were all measures families could take, she said.

The research is published in The Lancet.