Hygiene hypothesis could explain increased asthma risk
20 April 2009

Western European countries have much higher rates of asthma than those in Eastern Europe because children in the West grow up in more sanitised conditions, according to new research. 

While asthma prevalence in industrialised countries has risen, in Eastern Europe cases of allergic conditions such as asthma, hayfever and eczema have remained low.

One of the explanations offered for this difference is the hygiene hypothesis. According to this hypothesis, the lower prevalence in the East is due to frequent infectious diseases, lower rates of immunisation and greater exposure to bacteria.

Dr Michael Kramer and colleagues monitored 13,889 children in Belarus up to the age of 6.5 years, at which age the children underwent a physical examination. Parents were questioned about their child’s exposure to farm animals, pets and probiotics, and asked if they had wheezed or shown signs of allergies.

The researchers found that boys, children with allergies in their family, and those who had received probiotics, were all more likely to have wheezed or experienced hayfever symptoms in the past 12 months compared to other children.

Children whose mothers smoked after their birth were also more likely to wheeze or have hayfever, while breastfeeding was not protective against any of the studied outcomes.

However, pet ownership, contact with farm animals, the presence and number of younger and (especially) older siblings, and living in rural areas of Western Belarus were associated with reduced risks.

Dr Elaine Vickers, Asthma UK’s Research Relations Manager, said: ‘The hygiene hypothesis is a hot topic of debate in the research community. Some believe that our immune system, which is primed for fighting off a wide range of infections, somehow goes awry in our modern, sanitised environment, leading to increased rates of allergies and asthma. Others believe that it’s more to do with our genetic makeup and the number of severe viral infections we experience as a child.

‘Whatever the truth, the best advice we can currently give to parents is not to smoke around their children and make sure they have a balanced diet and get plenty of exercise.’