Household environments may affect the likelihood of children developing eczema

Household environments, including owning a dog, may affect the likelihood of children developing eczema, according to an analysis of almost 300,000 people from across Europe.

The prevalence of eczema has rapidly risen in industrialised areas over the past 30 years, now affecting approximately 20% of children and 10% of adults in high-income countries.

The new study, published in Allergy, examined data from 16 European studies, to investigate whether those who are prone to developing eczema might respond differently to environmental factors.

The researchers investigated interactions between the 24 most significant eczema-associated genetic variants and 18 early life environmental factors during the mother's pregnancy and the child's first year of life. Representing the largest and most comprehensive analysis of gene-environments interactions to date, the findings provide new insights into what could cause eczema in children and how environmental factors may influence genetic risk.

The international study team was led by researchers from the London School of Hygiene & Tropical Medicine (LSHTM), University of Edinburgh, University of Bristol and Helmholtz Munich.

An initial analysis of more than 25,000 individuals suggested there may be a relationship between seven environmental factors - dog ownership, having an older sibling, cat ownership, breastfeeding, smoking, antibiotic use and washing practices - and at least one established genetic variant that predisposes a child to eczema. In the further analysis of a larger group of almost 255,000 people, the only strong interaction found was between dog ownership and just one of the 24 eczema-associated genetic variations. Children or babies with that gene whose families owned a pet dog had a lower risk of developing eczema.

This genetic mutation is located near DNA that codes for interleukin-7 receptor (IL-7R) - a protein involved in immune cell function and inflammation. Lab tests confirmed that in human skin cells with the genetic variant, molecular signals from a dog can suppress skin inflammation instead of causing allergy.

These results are preliminary; however, they point to the IL-7R protein as a potential area of focus to inform prevention of eczema in some individuals. The study also found a similar effect among young children with older siblings, but further studies are needed to confirm the link. The researchers speculated that more microbial exposure at an early age, through contact with dogs and other children, could be behind the protective effect.

The authors stressed that the study did not look at the effect of dog exposure in the treatment of existing eczema, cautioning that introducing a dog may make symptoms worse in some children.

Despite the large number of people studied, the researchers did not have enough participants to draw meaningful conclusions on many gene-environment interactions, suggesting that only weak interactions are likely to exist. Further research involving a larger population, as well as greater diversity of ethnic background, is needed is needed to better understand interactions between genetic and environmental factors linked to eczema.

These results are an important step in understanding how environmental risks affect childhood eczema and how we might develop ways to prevent it. 

While exposure to dogs stands out as a factor worth exploring further, the results do not support exposure to a dog as an effective strategy to prevent eczema now. The study also helps rule out strong genetic interactions for many other environmental factors, which will help focus future research efforts."

Professor Sinéad Langan, lead author on the study and Professor of Clinical Epidemiology at LSHTM