Farm exposure in utero protects against asthma

An increasing number of studies have shown a reduced risk of allergies, hay fever, asthma and eczema in farmers' children and adolescents. Until recently it was believed that these protective effects primarily arise from exposures during the first years of life.

Jeroen Douwes (Massey University, Wellington, New Zealand) and colleagues examined the effects of current, early and prenatal farming exposures in children from farms, and in a rural non-farming reference population. For this purpose they surveyed 1,333 farmers' children and 566 reference children aged 5-17 years.

The authors confirm that symptoms and eczema are less common in farmers' children. More importantly, they show that maternal exposure during pregnancy to animals and/or grain and hay strongly reduces the risk of asthma symptoms, hay fever and eczema. This risk is even further reduced when children are also currently exposed. In fact, when children are exposed both in utero and later in life, asthma, hay fever and eczema are reduced by more than 50%.

Thus, prenatal exposure contributes to the low prevalence of asthma, hay fever and eczema in farmers' children, but continued exposure is required to maintain optimal protection. These findings suggest that to prevent allergic diseases, such as asthma, hay fever and eczema, measures should be taken before birth and may have to be continued throughout life.

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Last Reviewed: 8 October 2010
Next Review Date: 8 October 2012