Why your cat could give you asthma (but your dog won’t)

GROWING up with a pet dog protects children against asthma – but owning a cat increases the risk, research suggests.

A study of 20,000 children found having a pet dog before the age of three cuts the chance of asthma by 40 per cent.

But having a cat in those early years increases the risk by half, the Imperial College London researchers found.

Study leader Silvia Colicino believes this is because dogs are dirtier than cats, so they expose children to bacteria early in life.

This helps prime the immune system, triggering the production of antibodies that protect against allergies. Cats, on the other hand, tend to be much cleaner and less affectionate – they are less likely to give a child a slobbery lick – so do not pass on this bacteria.

Cats’ fur also carries tiny antigens – particles that trigger a response in the immune system – that can then lead to asthma.

The findings bolster the theory that the modern obsession with cleanliness has driven a boom in allergies and health problems.

According to the ‘ hygiene hypothesis’, exposure to a range of bacteria is necessary to develop the immune system early in life. About 5.4million Britons have asthma – one in every 12 adults and one in every 11 children.

Miss Colicino, who presented her findings at the British Thoracic Society’s winter meeting in London, said: ‘Pre-school children who live in a dirty environment with a high level of bacteria are less likely to develop allergies. Your body has to react to the bacteria by generating antibodies which are good at protecting against asthma. Dogs are dirtier than cats.

‘They tend to live outside and they carry high levels of bacteria. Early contact of children with dogs – up to two or three years old but especially in the first year of life – seems to protect against asthma.’

She said cats were more likely to be kept indoors, so the antigens in their fur circulate in the house.

The research team tracked children in Manchester, Bristol, Kent, the Isle of Wight and Aberdeen.

Using that data, scientists made a tool to forecast with 80 per cent accuracy which children were most likely to develop asthma.

Whether there is a dog or a cat in the house are key elements of the tool, along with early wheezing, hay fever and if the child’s parents have a history of allergies.

Miss Colicino, who worked with experts from the universities of Southampton, Bristol and Manchester, is expecting to publish the full results next year.

She said: ‘Our research showed there were many factors which can predict whether children will go on to have asthma by the age of 20.

‘For example, a child with wheezing symptoms and eczema in early childhood is over 75 per cent more likely to develop asthma up to the age of 20 years compared to a wheezy child without eczema at pre-school age. It is a mixed picture that we need to analyse further.’

Dr Erika Kennington, of Asthma UK, said: ‘ It’s important to remember that all animals, including dogs and cats, produce dander, urine and saliva that can also trigger asthma symptoms.’

‘Body reacts to the bacteria’