Do furry creatures increase – or decrease – the risk of allergy?
by Tara Haelle
Allergies suck. If there were concrete steps you could take to reduce the risk your child would develop allergies, it’s probably safe to say you would take them. But would that include getting rid of your “child” before you had children – such as your dog or cat?
If the question were whether you would get rid of a pet who had bitten your child, especially multiple times, the answer may be a bit simpler: these tend to be more serious injuries, and they may indicate a developing pattern of behavior. But the research on how pets do or don’t affect the allergies risk is far shakier. The question involves two unproven theories: the allergen hypothesis, which initially suggested that exposure to allergens can sensitize individuals but has now flipped to suggest early exposure can build a tolerance, and the hygiene hypothesis, which suggests that not having regular exposure to lots of germs in childhood can increase the risk of allergies because the immune system doesn’t develop fully.
The problem is that both these hypotheses are incredibly difficult to test. The development of autoimmune conditions are complex and not entirely understood, potentially involving many different interacting factors. The only clearly established risk factor is having a family history of allergies. There are no randomized controlled trials in which families are randomly assigned to own a pet or not own a pet, a study that’s unlikely ever to happen. And we cannot raise kids in laboratories that would allow sufficient control of environmental factors. So we’re stuck making sense out of incomplete observational studies, which involve so many other variables that it’s tough to determine what is or isn’t contributing to (or preventing) allergies. Dozens of studies have explored whether dogs, cats, rodents and birds are linked to asthma, eczema, wheeze, hay fever, and other forms of allergies, but even in high-risk children – those with a family history of allergies – the research is equivocal. In fact, families with a history of allergies are already less likely to have pets, so it’s not possible to entirely account for that confounder, which can make it look as though not owning a pet is linked to allergies. Further, allergy risk would depend on types of pets and breeds, how much exposure the children have to the animals, whether the animals are indoor or outdoor, what pets nearby neighbors might own, the geographical area and environmental allergens, the children’s genetics… and so on.
But we can still have a look at what has been found to date, keeping in mind a couple important caveats. First, studies differ a great deal in how they measure family history and children’s outcomes as well. Second, most infrequent wheezing – a sign of allergy – in children younger than 6 will eventually go away on its own. Third, the variables each study does control for vary almost as much as the number of dog breeds out there.
One analysis of 11 European studies found a small amount of evidence to show that having a furry pet in a child’s first two years reduced their sensitization to allergies in the air – that is, making it less likely they would develop allergies. Another older analysis of 32 studies found cats decreased asthma risk while dogs increased it. But then, one large much more recent meta-analysis of 21 studies found owning dogs or pets in general, though not necessarily cats, reduced the risk of a type of eczema as much as 25 percent. (See what I mean?) The only thing resembling a consensus is that owning a dog when a baby is a newborn appears to slightly decrease the risk of some allergies, eczema and/or asthma, but the effect is weak, it mostly applies to those without a history of allergy, and there are still many other factors that could play a role.
The extent to which owning a dog or cat can reduce allergy risk, then, is still uncertain, but the good news is that the most recent studies, especially long-term ones, don’t find owning a dog or a cat in early childhood increases a child’s risk of developing allergies. A different question is whether being born into a dog- or cat-owning home might play a role in allergies later on, when children grow up and get a dog or cat on their own. It appears that owning a dog or a cat in early childhood might slightly decrease this risk, but the effect is again weak.
If a child does end up being allergic to dogs or cats, there are a variety of hypoallergenic breeds that might work (though there no such thing as a 100 percent hypoallergenic dog or cat). Or, if a child develops an allergy to a beloved furry creature who is already a part of the family, then the deliberations about what to do should involve an allergist. Aside from these situations involving known, diagnosed allergies, about the only consensus on pets and allergies is that concerns about allergy development should not be factor in whether to get or give up a pet dog or cat.