Dishing the dirt

Did you wake up this morning to the sound of a wheezing child? Does summertime mean sneezing, and the merest whiff of a cat turn your infant into a sniffling wreck? If so, you are not alone: one in three children in Britain today suffer from an allergic disorder like asthma or hayfever. The good news is that you may be able to do something about it. A study presented yesterday at a meeting of the European Respiratory Society in Madrid shows that young children and infants who are in regular contact with farm animals are less likely than others to develop allergies later in life.

Over the past 20 years incidences of asthma and eczema have increased four-fold in the UK. The usual explanation - though there is scant medical proof - is that we are increasingly exposed to sensitising allergens and pollutants, eat a diet rich in protein and saturated fats, and don't eat enough fruit and vegetables. But this most recent study, a joint effort by the Paediatric Pulmonology Department of the children's hospital and the Public Health Department of the city of Salzburg under Dr Josef Riedler, offers an alternative explanation.

Dr Riedler looked at 2,283 Austrian children aged between 8 and 10 and found that those living on farms are more than three times less likely to suffer from asthma, half as likely to suffer from other allergies and three times less sensitive to hay fever than children who live in a non-rural environment. Of course, you might argue that country air is "healthier" than city air and country children probably eat better and get more exercise than city children do. But the study takes into account such variants as eating habits, genetic background, parental education and living conditions. And still the difference between farm and non-farm children is marked.

This does not mean that if you want your baby to breathe easy you have to become a farmer. Merely taking your little one to visit farm animals can make a big difference. When Dr Riedler tested what happens if children had regular contact with cows or poultry - regardless of their home environment - he found that the gap between town and country dwellers closed substantially. This shows, then, that what really matters is frequent exposure to the animals, not whether your child actually lives on the farm.

There is, as yet, no clinical explanation of why some children develop protection against allergies, while others dissolve at the slightest whiff of dust or pollen. But Dr Riedler believes it could be down to "the development of immune tolerance by increased exposure to microbial antigens in the stables or farm houses". In other words, children who are exposed to farmyard dirt build up antibodies and are less likely to suffer from allergies than those who are kept away from muck.

But don't smear your child in dung just yet. Dr Paul Cullinan, consultant in occupational and environmental medicine at the Royal Brompton hospital, London, points out that, while generally convincing, the farming theory "may not be as simple as it sounds". It is possible, for instance, that farming communities may be self-selecting. "If you're allergic," Dr Cullinan points out, "you probably don't take up farming."

Still, the notion that dirt is good for children is not a new one. The "dirt hypothesis" was first put forward 10 years ago by Professor David Strachan of St George's Hospital medical school in London. Strachan found that children from large families who are exposed to infections at a young age are less likely to develop allergies than children from smaller families, raised in "cleaner" environments.

Subsequent clinical investigations have borne this theory out. One study, in April this year, looked at 14,000 children in Bristol and found that those who bathed daily and washed their faces and hands three or four times a day had a one in five chance of having asthma. But those who bathed every other day and washed less frequently only had a one in seven chance. Even more convincing still are the recent preliminary clinical trials carried out by Stephen Holgate, professor of immunopharmacology at the university of Southampton. These showed that a "dirt vaccine" made from dead African soil bacteria could alleviate up to 30% of the symptoms suffered during an asthmatic attack.

The belief, then, is that children whose immune systems are not challenged by conventional microbes may subsequently become allergic to less conventional allergens, like dust mites. So by bleaching your kitchen so efficiently, you may be protecting your child from bacteria and infection but at the same time you are preventing him or her from developing natural resistance to dust and other irritants. And doctors know that immune reactions are linked to a child's likelihood of developing asthma. "Children who have poor reactions to the BCG vaccine early in infancy are those that tend to develop asthma and allergic disease", says Holgate.

Dr Riedler's farmyard study, then, should be seen as an important extension of an on-going "dirt hypothesis" which looks highly likely, but lacks detailed explanation. However, before a rash of chicken coops springs up across London, the European Respiratory Society injects a note of caution. Professor Kai-H kon Carlsen, head of its Pediatric Assembly and director general of the Voksentoppen National Hospital in Oslo, warns that "previous studies have shown that early allergen contact (during the first year of life) may predispose to allergy later in life". And before you thrust your child into the jaws of the farmyard dog, use a bit of common sense. "Children who have developed an allergy towards domestic animals," says Carlsen, "should keep away from those animals in order to counteract a more severe development of the disease." But the basic theory still stands, so if you want an allergy free child, cancel that subscription to the Sneeze Gazette, and head (cautiously) for the farmyard.

Thanks to guardian.co.uk who have provided this article. View the original here.