People who lived on farms during early childhood have a lower risk of developing allergies as adults, a new study has found.

The findings also suggest that women who lived on farms in early childhood have stronger lungs.

In recent decades, there has been a big increase in the prevalence of asthma and allergies. Some researchers have suggested that children who are exposed to a high number of potential allergens and microbes may have a reduced risk of developing allergies - this is known as the hygiene hypothesis.

Australian researchers decided to look into this further. They assessed data from a health survey that involved over 10,000 people in 14 countries in Europe and Australia between 1998 and 2002.

The participants were asked about where they had lived before the age of five - on a farm, in a rural village, in a small town or city suburb, or in the inner city. They also reported their exposure to a number of things, including pet cats and dogs, siblings and other children in childcare/school.

Their lung strength was also assessed and they provided details about any allergic symptoms they had, such as asthma, hay fever, nasal symptoms and wheeze.

The study found that children who grew up on a farm were more likely to have had pet animals, older siblings and to have shared a bedroom when they were young. They were also less likely to have a history of family allergies.

As adults, those who had lived on farms were less likely to react to allergens than those living in any of the other environments, including those living in rural areas. They were also less likely to display nasal symptoms or have over-reactive airways.

Overall, those who had lived on farms in early childhood were 54% less likely to have asthma or hay fever and 57% less likely to have allergic nasal symptoms. compared to those who lived in the inner city.

Even those living in rural villages were only slightly less likely to have developed asthma or hay fever as adults compared to those living in the inner city.

The study also found that women who had lived on farms before the age of five had stronger lungs compared to those who had lived in inner cities. This finding was consistent across all 14 countries studied.

While this is an observational study, so no firm conclusions about cause and effect can be drawn, the researchers concluded that ‘the consistency of the findings across multi-country settings suggests that farming effects may be due to biological mechanisms rather than socio-cultural effects that would differ between countries'.

Details of these findings are published in the journal, Thorax.