Do Dogs Lower the Risk of Allergies and Asthma in Children?

Early contact with dogs might influence the immune system – but the evidence is not clear-cut.

In brief

For decades, the advice was that families at risk of allergies should not get a dog. Some research has softened that picture: a number of large observational studies link early contact with dogs to a slightly lower risk of asthma and allergic sensitization. Other analyses, just as large, find no clear association. The most plausible explanation for any protection is the greater microbial diversity a dog brings into the home – but the strongest mechanistic evidence for this comes from animal experiments, not from humans. In short: a plausible protective hypothesis, with data that remain contradictory. Either way, a dog is not a medical preventive measure.

Dogs have been at our side for thousands of years. Beyond their emotional importance, one question has moved into the research spotlight: can early contact with dogs influence a child’s immune system – and perhaps even protect against allergies or asthma? We’ll walk you through the evidence, explain the role of the microbiome and the hygiene hypothesis, and deliberately stick to what the data actually support.

First: three terms that are often confused

Before we get to the studies, an important distinction that many guides skip over. Allergic sensitization initially means only that the immune system reacts to certain allergens – detectable, for example, in a skin prick test. It is not the same as a clinically noticeable allergy: a child can be sensitized without ever developing symptoms. And asthma is not a single uniform disease; it can be allergic or non-allergic in nature. A lower sensitization rate therefore doesn’t automatically mean fewer allergies or less asthma. Keeping these endpoints cleanly apart is the key to reading the studies correctly.

1. From risk factor to possible protective factor

For a long time, the recommendation was to avoid pets in households with young children, especially when allergies ran in the family. From the early 2000s on, studies began to question this picture.

One influential study was Ownby et al. (2002). In a birth cohort in the Detroit area, children who grew up with two or more dogs or cats in their first year of life showed allergic sensitization less often at age 6–7 than children without this contact. The association was clearest with several animals; a single dog gave a less clear picture.

The Swedish registry study by Fall et al. (2015), covering more than one million children, found that exposure to dogs in the first year of life was associated with an approximately 13% lower risk of asthma in school-age children (odds ratio 0.87). Two limitations belong right alongside this: in children under three, no such association could be shown, and “dog exposure” was measured only by whether a parent was registered as a dog owner – a rough approximation. Still, the results remained comparable when the analysis was restricted to firstborn children, which argues against pure avoidance bias.

2. But: the overall picture is more contradictory than individual studies suggest

Honesty is called for here, because the choice of studies determines the result. A large harmonized analysis of more than 77,000 mother–child pairs from nine European birth cohorts (Pinot de Moira et al., 2022) found no statistically clear association between dog ownership and asthma: an odds ratio of 0.92 with a confidence interval of 0.85 to 1.01, which just barely includes 1.0. Nor was there a clear effect for dog-specific sensitization, and neither the timing nor the number of dogs changed this much.

So if you summarize the literature, there is no consistent picture: some studies point toward a possible protective effect, while others find no association or different results. A microbial mechanism is biologically plausible but has not been clearly demonstrated in humans.

3. The role of the microbiome: dogs bring diversity into the home

Where would any protection come from in the first place? One plausible answer lies in microbial diversity. Dogs move around outdoors, come into contact with soil, plants, and a wide range of environmental microorganisms, and carry these into the home on their coat and paws.

Fujimura et al. (2010) compared the microbial community in house dust from homes with and without dogs. Dog homes showed higher bacterial diversity and an altered, in part lower diversity of the fungal species detected. This is a descriptive, correlational finding – it shows that the microbial environment differs, not that it necessarily protects.

The step from association to mechanism comes from animal research: in Fujimura et al. (2014), mice exposed to dog-associated house dust were better protected against an experimental airway allergen challenge. Their gut microbiome was enriched with the bacterium Lactobacillus johnsonii, which, given on its own, could provide part of the protection. A strong hint at a possible pathway – but in a mouse model. Whether it works the same way in humans has not been shown.

4. The hygiene hypothesis and “Old Friends”

These associations are often discussed within the framework of the hygiene hypothesis. For context: it is an explanatory framework that is still being debated and developed – not an established mechanism. Strachan (1989) noticed that hay fever was less common in children with many older siblings. The name, however, is now recognized as misleading: it isn’t about a lack of household cleanliness but about the diversity of early microbial contacts. Its further development, the “Old Friends” hypothesis (Rook, 2010), assumes that humans co-evolved with certain microorganisms and that early contact with them could influence how immune regulation develops. This, too, is an explanatory model, not an established pathway.

The context remains important: lower diversity of certain early environmental contacts is discussed as one of several factors that could influence how immune regulation develops – alongside genetics, the skin barrier, diet, medications, air pollutants, and infections. In this model, a dog acts as a natural bridge that brings environmental microbes into the home.

5. Timing could play a role

Several studies suggest that it’s not just whether but above all when contact takes place that plays a role. Ownby et al. (2002) found the clearest association with contact in the first year of life; in Fall et al. (2015), the association with asthma risk appeared in preschool and school-age children but not in children under three. For cats, there are similar indications, which tend to be weaker and less consistent.

It remains largely unclear which characteristics of dog ownership might be decisive. Contact with nature, time spent outdoors, and the dog’s individual microbiome are among the possibilities. So far, however, there are no robust data from which concrete recommendations could be derived.

6. Beyond immunology

Regardless of any immunological effects, owning a dog can encourage physical activity, social activity, and subjective well-being. These effects, however, vary from person to person and should be kept separate from the allergy and asthma risk discussed here. We give an overview in How dogs can benefit their owners’ health.

7. What the research does (not yet) show

This is the context that separates a serious article from an oversimplified headline:

• Association is not causation. Almost all human data come from observational studies – they show things occurring together, not necessarily a chain of cause and effect.
• Avoidance bias. Families with a strong allergy burden are less likely to get a dog, which can create the illusion of a protective effect. Good studies try to adjust for this – it can’t be ruled out completely.
• Inconsistent results. Large analyses reach opposite conclusions (compare Fall et al. 2015 vs. Pinot de Moira et al. 2022).
• Mechanism mostly from animal studies. The most convincing causal evidence comes from the mouse model.
• Rough exposure measures and modest effect sizes: a risk that differs by a few percent in relative terms says little about any individual case.

8. What guidelines recommend

The current German-language S3 guideline on allergy prevention (2022) does not recommend getting a dog for the purpose of preventing allergies – but it explicitly states that dog ownership should not be discouraged, even for children at increased risk of allergies. For pets already in the home, there is no evidence for giving them up for prevention reasons. Cats are a different matter: getting a new cat tends to be discouraged when the risk is increased.

In practical terms: if allergies run in the family, there is no need to rule out a dog as a matter of principle. If, however, the child or other household members already have symptoms around dogs, a confirmed dog allergy, or poorly controlled asthma, the decision should be evaluated by an allergist. And regardless of any health question: a dog is a living being with needs of his own – the decision to get one should come from conviction, not from hoping for a side effect.

Conclusion

Early contact with dogs might have a favorable influence on a child’s immune system, and the greater microbial diversity in the home is a biologically plausible candidate for this. In humans, however, this protection has not been proven: the epidemiological evidence remains contradictory, and the most convincing mechanism comes from animal research. The fairest summary is: a plausible protective hypothesis, with data that remain inconsistent.

In any case, a dog’s value goes far beyond immunology. If you give your dog a life that suits his species, with plenty of exercise and time in nature, you are first and foremost doing him good – and perhaps supporting a healthy family life along the way. He is no guarantee of an allergy-free life. But he can very well be a valuable part of a healthy lifestyle.

References

Primary studies

Fall, T., Lundholm, C., Örtqvist, A. K., et al. (2015). Early exposure to dogs and farm animals and the risk of childhood asthma. JAMA Pediatrics, 169(11), e153219. https://doi.org/10.1001/jamapediatrics.2015.3219

Pinot de Moira, A., Strandberg-Larsen, K., Bishop, T., et al. (2022). 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. Journal of Allergy and Clinical Immunology, 150(1), 82–92. https://doi.org/10.1016/j.jaci.2022.01.023

Fujimura, K. E., Johnson, C. C., Ownby, D. R., et al. (2010). Man's best friend? The effect of pet ownership on house dust microbial communities. Journal of Allergy and Clinical Immunology, 126(2), 410–412. https://doi.org/10.1016/j.jaci.2010.05.042

Fujimura, K. E., Demoor, T., Rauch, M., et al. (2014). House dust exposure mediates gut microbiome Lactobacillus enrichment and airway immune defense against allergens and virus infection. PNAS, 111(2), 805–810. https://doi.org/10.1073/pnas.1310750111 (animal model)

Ownby, D. R., Johnson, C. C., & Peterson, E. L. (2002). Exposure to dogs and cats in the first year of life and risk of allergic sensitization at 6 to 7 years of age. JAMA, 288(8), 963–972. https://doi.org/10.1001/jama.288.8.963

Bufford, J. D., et al. (2008). Effects of dog ownership in early childhood on immune development and atopic diseases. Clinical & Experimental Allergy, 38(10), 1635–1643. https://doi.org/10.1111/j.1365-2222.2008.03018.x

Reviews, hypothesis papers, and guidelines

Kopp, M. V., et al. (2022). S3-Leitlinie Allergieprävention. AWMF-Register-Nr. 061-016. Allergologie select, 6, 61–97.

Strachan, D. P. (1989). Hay fever, hygiene, and household size. BMJ, 299(6710), 1259–1260.

Rook, G. A. (2010). Darwinian medicine and the 'hygiene' or 'old friends' hypothesis. Clinical & Experimental Immunology, 160(1), 70–79.

Key takeaways

The earlier recommendation is viewed differently today – “better no dog in at-risk families” has turned into a debated possible protective factor. The evidence for this is considerably weaker than headlines suggest.

The evidence is contradictory. Large cohorts and meta-analyses reach different results depending on country, age, and the endpoint studied.

Three terms are regularly confused: sensitization, allergy, and asthma are not the same – a study can find an effect for one and not for another.

One possible mechanism lies in the microbiome: dogs bring more microbial diversity into house dust. In humans, however, this pathway has not been clearly demonstrated.

Timing could play a role. The findings relate mostly to early exposure in the first year of life – this does not establish a confirmed time window.

Association is not causation. Families who decide to get a dog differ in many ways from families without one.

The German-language S3 guideline on allergy prevention does not recommend getting a dog for prevention – but it doesn’t advise against it either, even when the risk is increased.

Dogs already in the home should not be given up for prevention reasons. There is no evidence for doing so.

Existing symptoms around dogs are a different matter – then a doctor should evaluate them, instead of relying on prevention findings.

Frequently asked questions about allergy and asthma risk