It could seem logical that growing up with a cat or a dog would increase your risk of developing asthma or allergy to those animals.
But there is also evidence suggesting that early exposure to allergens may induce immune tolerance, where you no longer respond to the allergen when exposed.
So what should you believe? A new study from the University of Copenhagen comes to aid new parents struggling to decide if they should keep their pet or not.
“Our findings suggest that early-life cat and dog ownership in itself is unlikely to increase the risk of asthma. Having such a pet in the first years of your life also does not increase your risk of developing cat or dog-specific allergic sensitization,” explains Postdoc Angela Pinot de Moira, first author of the new study, which was published in Journal of Allergy and Clinical Immunology.
The study defines early-life as your child being two years old or less.
“If you own a cat or a dog, and your child does not develop sensitization, there may actually be a slightly protective effect against asthma. But if your child develops sensitization to cats or dogs, our evidence suggests there might be an increased risk of developing asthma, in which case ownership should possibly be avoided,” says Angela Pinot de Moira at the Department of Public Health.
Although one previous European study demonstrated no overall association between early-life cat and dog exposure and school-age asthma, the new findings suggest that the picture may be more complicated and point to potentially a small protective effect in the absence of sensitization and harmful effect in the presence of sensitization.
Angela Pinot de Moira also explains, that children might gain some small protection against the risk of developing sensitization to other allergens than cats or dogs, if they had a cat or a dog in the first two years of their life.
Pets may change our microbiome
The researchers speculate that the protective effect could be the result of being exposed to cats’ or dogs’ microbiota, which may be beneficial to the developing immune system.
“We have not looked into the mechanisms behind that in this particular study, but we have another study on the way, where we use data from the Danish National Birth Cohort to study exactly this. Other studies have done something similar by looking at how having a pet can change the composition of our microbiome,” says Angela Pinot de Moira.
The new study is a statistical one, including data from more than 77,000 European children, utilizing the EU Child Cohort Network database available to researchers. Data were analysed using an open-source software called DataSHIELD, a novel technological solution to sharing data which complies with GDPR law. When data are analysed using DataSHIELD, only summary statistics are ever visible to the researcher, and a number of filters ensure data are never disclosed.
A total of nine different cohorts were included, and some of those had sub-cohorts with measures of allergic sensitization. Those measurements involved either measuring IgE (an antibody often involved in allergic reactions) in the blood to cat or dogs, or doing skin prick testing.
“It is hard to look at allergic sensitization in whole birth cohorts and/or all of the cohorts, since it requires a lot of measurement. So the analysis using these data was a sub-analysis in some of the cohorts, and the numbers are fairly small when it comes to the connection between cat or dog ownership, allergic sensitisation and the risk of developing asthma,” explains Angela Pinot de Moira.
However, the researchers observe the same patterns between cat ownership and risk of asthma, as well as dog ownership and risk of asthma, which strengthens the evidence slightly.
“Further meta-analyses are required to confirm our findings, but our results will help inform future studies, which could lead to some clearer guidelines regarding early-life cat and dog ownership,” she says.
Reference: Pinot de Moira A, Strandberg-Larsen K, Bishop T, et al. Associations of early-life pet ownership with asthma and allergic sensitization: A meta-analysis of more than 77,000 children from the EU Child Cohort Network. J. Allergy Clin. Immunology. 2022. doi: 10.1016/j.jaci.2022.01.023
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