Childhood Pet Exposure: Implications for Asthma and Eczema Risk
The rising prevalence of allergies worldwide continues to raise important questions for healthcare professionals about why some individuals develop conditions like asthma and eczema while others do not. Among the long-discussed theories is the hygiene hypothesis, which suggests that modern lifestyles—characterized by increased indoor living, reduced family sizes, and more rigorous hygiene—limit early-life exposure to microbes that would otherwise help educate the immune system. This reduced microbial exposure may contribute to immune dysregulation and heightened allergic susceptibility. However, emerging research is highlighting the intriguing possibility that living with pets might counterbalance some of these effects by introducing a diverse array of microbes into the household environment.
Early childhood is a critical period during which the immune system learns to distinguish harmful pathogens from benign exposures such as food proteins, pollen, dust, and dander. Failures in this complex education process can lead to immune overreactions to otherwise harmless substances, manifesting as allergic diseases of the skin, airways, or gastrointestinal tract. While genetic factors undoubtedly play a role—certain gene variants can raise the likelihood of developing atopic diseases—they typically act as risk factors rather than direct causes. Increasingly, research is focusing on the interplay between genetics and environmental exposures, especially those shaping the gut microbiome. From birth, the infant gastrointestinal tract becomes colonized by diverse microbes, establishing a dynamic ecosystem that communicates extensively with the developing immune system. Perturbations in this “crosstalk,” particularly reductions in microbial diversity, have been associated with chronic inflammation and a spectrum of noncommunicable diseases.
Insights into how early environments affect allergy risk first emerged from studies of children raised on farms. These children, often in frequent contact with livestock and exposed to barns, soil, and unprocessed foods, consistently show lower rates of conditions like asthma and eczema compared to peers raised in urban settings. This protective effect is partly attributed to a richer, more diverse microbiome, which seems to train the immune system toward greater tolerance. However, with global urbanization accelerating, fewer children are growing up in these traditional environments. In many urban households, pets may serve as the primary source of regular exposure to environmental microbes.
Research on whether domestic animals can meaningfully reduce the risk of allergic diseases is evolving, with some encouraging findings. For eczema, evidence from a systematic review of 23 studies indicates that early-life exposure to dogs is associated with a significantly lower risk. Moreover, a recent large-scale genetic study involving over 270,000 individuals found that a gene linked to eczema only increased disease risk among those who had not been exposed to dogs in early childhood. This suggests that living with a dog might mitigate genetic susceptibility to eczema, offering a tangible example of gene-environment interaction.
Asthma presents a more nuanced picture. A well-known longitudinal study that followed over a thousand U.S. children from birth to adolescence reported that living with a dog indoors was associated with reduced frequent wheezing—but predominantly among children without a family history of asthma. Meanwhile, a Korean cohort study found that childhood dog ownership was linked to a reduced risk of developing allergies overall, yet paradoxically showed a slight increase in non-allergic wheezing, which is often tied to airway irritation or respiratory infections rather than allergen sensitivity. This dual finding underscores the complexity of pet-associated exposures: while they might help steer the immune system away from allergic pathways, they could simultaneously elevate the risk of some non-allergic respiratory symptoms.
When examining cats separately from dogs, the protective signal against allergy is less clear. Some studies that differentiated between types of pets found no evidence that living with cats reduced allergy risk. This discrepancy might stem from fundamental differences in the types of microbes cats and dogs introduce into household environments. Dogs frequently go outdoors and may bring back soil- and plant-associated microbes, potentially contributing to a more farm-like microbial exposure. In contrast, cats, especially indoor ones, might have more limited ecological overlap with these environments.
For clinicians advising families, the current body of evidence suggests that if parents are already considering getting a dog, early-life exposure could offer an added benefit of potentially lowering the risk of eczema and perhaps other allergic conditions. However, it is essential to counsel that pet ownership is not a guaranteed safeguard against allergies and should be pursued primarily for the companionship and enrichment it brings. Importantly, promoting a diverse range of environmental exposures remains advisable regardless of pet ownership. Encouraging children to spend time outdoors, engage in unstructured play that might involve getting dirty, and avoiding excessive use of disinfectants are all practical strategies to support the development of a resilient, well-regulated immune system.
As the field advances, further research will continue to clarify how microbial exposures from animals and the broader environment interact with genetic factors to shape allergy risk. This knowledge may ultimately inform more personalized approaches to allergy prevention, underscoring the importance of integrating environmental considerations into early-life care discussions.