Why do they matter?

Allergy to cats is quite common and results in a streaming nose and eyes and sometimes in wheezing. The allergy is to one or more proteins that cats produce - especially in their saliva. When washing themselves, this is transferred to their fur; once the protein has dried out it can become airborne.

In Latin, the house cat is known as Felis domesticus. The most important cat allergen is termed Fel d1. It is carried on very fine particles which can be found in the air of most British homes, even those where there is no cat. The same particles can be found on clothing, on soft furnishings in the home and even on bus and cinema seats. Because the particles are very fine, they remain suspended in the air for a long time; people with allergies to cats often get symptoms within minutes of going into a room where a cat has been. If a cat is removed from a home - for one reason or another - it takes around six months for the allergen to disappear completely.

What did we do?

Around two months after each child was born, we used a modified household hoover to collect samples of 'dust' from their living rooms and mattresses. These samples were sent to our laboratory in London where they were tested for the quantity of cat protein (allergen) they contained. This allergen is called Fel d1. In this way we have been able to make a rough estimate of the level of Fel d1 each child encountered in their first months of life. Eventually we will be able to examine whether those children who met high levels of cat allergen were more likely to develop asthma.

We also asked parents to tell us whether they kept a cat, dog or other pet - and if so, how many.

What did we find in Ashford?

One third of homes kept one or more pet cats:

How many cats do people keep? number of homes in the Ashford study

Not surprisingly, the levels of Fel d1 in living room carpets were higher in homes with cats than in homes without; where there were several cats the levels were sometimes very high. Even in homes without pet cats however (96% of them in fact), we could still detect allergen. This probably reflects dust carried from one home to another - often on children's clothing.

Cat allergen levels were higher where more cats were kept cat allergen levels (ug per gram of dust) number of cats in the home

Interestingly, homes where there were more children had a lot lower levels of Fel d1 - even if they had the same number of cats. We don't know why this should be so but wonder whether it reflects the different behaviour of cats when there are more people about; perhaps they spend a greater part of their time outdoors.

Cat allergen levels are lower when there are more children in the home cat allergen levels (ug per gram of dust) number of children in the home

Again the levels of cat allergen in the babies' beds were low; on average 1.2µ/g of dust compared to 3.1µg/g in the living room carpets. There was a huge range of values, from the lowest of 0.003µg/g to the highest of 990µg/g. Even where there was no pet cat in the home we found allergen in 78% of the babies' beds.

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