Can Having Pets Prevent Asthma?
Whether having a pet as an infant causes or prevents childhood asthma has long been debated. Much research has been done with varying conclusions, and expert opinion seems to change like the moulting of winter fur. After reading many articles on the subject, I figured it was time to sink my claws into the current findings to find the truth.
According to the World Health Organisation, in 2014, 235 million people worldwide suffered from asthma. It is the most common non-communicable (non-infectious) disease among children.
3 Types of Asthma
The condition can be classified as either ‘atopic’, ‘non-atopic’ or ‘mixed’.
Atopic asthma is sometimes called allergic asthma. This type of asthma is an allergic response to particles (allergens) suspended in the air and breathed in through the mouth and nose. These allergens may be dust particles, or in the case of pet-allergic asthma, pet dander or feather dust. Cat-allergic asthma is actually an inflammatory response to a protein in cat saliva that is coated on their fur when they wash themselves and then wafted around the house as they moult. Euuuuwwwwww….
There is often a genetic (inherited) component to allergic/atopic asthma, referred to in medical studies as ‘parental atopy.’ This is just a fancy-pants way of saying ‘family history of asthma.’
Non-atopic asthma occurs secondary to chronic or recurrent chest infections. Some research suggests this is triggered by a hypersensitivity to certain bacteria and viruses, though for the most part, non-atopic asthma can be thought of as non-allergic asthma.
Mixed asthma is when a person has a combination of both atopic and non-atopic asthma.
Does Having a Pet as an Infant Cause or Prevent Asthma and Allergies?
The answer is quite complex. Although most studies suggest that early exposure to pets can reduce a child's sensitivity to many allergens, there are a lot of factors that can affect this outcome. In this article, we will discuss the evidence put forth by these studies, the pitfalls of the study designs, and what this means for your child.
Study 1: The Effects of Having Pets on the Risk of Developing Allergies in the First Two Years of Life
You’ve no doubt heard the argument that kids these days are ‘far too clean.’ Apparently, back in the day, when young children ate mud, made dens, and shared their dog’s bed, no one had any problems—well, certainly no problems with asthma and allergies, anyway. But how true is this actually?
Well, as a keen lover of research, I like nothing better than to doggedly sift out fact from fiction. Here’s the low-down from the scientific studies I found:
In 2007, Pohlaben and colleagues published a study of 1881 German children, investigating whether early exposure to pets affected a child’s risk of developing allergies. New mothers were recruited from five different hospitals in Germany between the years 1999 and 2000 to take part in this study. Before heading home with their new bundle of joy, the mothers completed a lifestyle questionnaire that included a section on pets. Two years later, the same women were asked to complete a second questionnaire, detailing whether their child had ever been medically diagnosed with asthma, eczema, or hay-fever.
The researchers considered the children in two groups: 1) those with no family history of asthma or allergies (referred to as no parental atopy), and 2) those whose parents did suffer asthma or allergies (parental atopy). For children with no parental atopy, having a pet as an infant was associated with significantly less asthma and allergies by age two.
Cats, dogs and birds were included in the umbrella term ‘pets,’ although the protection against developing asthma and allergies was largely attributed to dogs. Check out the dog stats, below.
Results for Children With No Family History of Asthma
Percentage of children who developed asthma or allergies
Living without a dog as an infant
Living with a dog as an infant
In the group of children with no parental atopy, it seems that all those playtimes with Rover reduced diagnoses of allergies and asthma by almost a half.
However, for children with parental atopy, having a pet as an infant was associated with significantly more asthma and allergies. Again, this pattern in the results was largely attributed to dogs so the dog stats are included below.
Results for Children With a Family History of Asthma
Percentage who developed asthma or allergies
Living without a dog as an infant
Living with a dog as an infant
In the group of children with parental atopy, Rover’s presence in the home increased the development of allergies and asthma by almost one-and-a-third.
Study 2: Does Pet Ownership in Infancy Lead to Asthma or Allergies at School Age?
In 2012, Lodrup Carlsen and colleagues published a meta-analysis (a study of studies) investigating whether pet ownership in infancy leads to asthma or allergies at school age. Data were pooled from 11 European studies involving over 22,000 children.
The researchers looked at whether the participating children had lived with a furry or feathered pet between birth and their second birthday. They then investigated whether those same children, aged 6-10 years, suffered from asthma, allergic rhinitis (itchy, sneezy, snotty-nosed symptoms) or were sensitivity to airborne allergens.
Children who’d had pets were found to have significantly less sensitivity to airborne allergens compared to those who hadn’t. However, there was no such pattern between owning pets and the development childhood asthma. After looking at all the data, the authors concluded that having a pet in infancy neither increased nor decreased a child’s risk of developing asthma; the study failed to find any link at all.
Study 3: Perinatal Dog and Cat Exposure and the Risk of Developing Asthma
Also in 2012, Lodge and colleagues published a systematic review (another study of studies) of perinatal dog and cat exposure and the risk of asthma. Data were collected from nine studies involving 6498 participants. Their findings echoed the findings of Pohlaben’s study (Study 1); for children who had no family history of asthma or allergy, having a cat or dog as a young infant seemed to protect against allergies and allergen sensitivity. For the ‘high risk’ children however (those with a family history of asthma or allergies), having a cat or dog increased their risk of developing allergic disease.
Study 4: Pet Ownership and the Risk of Non-Atopic Asthma and Atopy
Most recently, in 2014, Collin and colleagues published a study of 3768 children, born in the United Kingdom between 1991 and 1992. The researchers investigated whether the children had pets at birth or during their infancy and whether they had developed asthma or allergen sensitivity by the age of seven.
They found that atopic (allergic) asthma was far less prevalent in the group of children who had lived with a cat, dog, rabbit or bird during infancy. The pet-owning group of children was also less sensitive to grass, dust-mite, and cat allergens, as measured by skin-prick testing.
However, the study also found that levels of non-atopic (non-allergy driven) asthma were higher in the group of children with pets. This was especially true for those children with rabbits or rodents. Additionally, living with rodents seemed to increase a child’s sensitivity to rodent allergens.
Correlation Does Not Mean Causation
The Drawback of These Studies: Confounding Variables
Clearly, the idea that pets prevent asthma is more than just an old wives’ tale. Indeed, numerous scientific studies support the concept. However, not all researchers agree on the validity or the extent of the protective effect of pets. The varying conclusions are perhaps because the evidence-base is dominated by cohort studies. That is, observational studies of people living their lives. Unfortunately, in research, studies of people living their lives come with the baggage of many confounding variables that may affect the results but cannot be controlled for.
To better understand what I mean, consider these two couples:
Ben and Josie
- Ben and Josie both have atopic (allergy-driven) asthma and are allergic to all fur-covered pets.
- They live in a pet-free home because of their asthma and allergies.
- Ben and Josie have two children, Milo and Sorrell. By the time they have reached middle school, both children have been diagnosed with pet-allergic asthma.
Mark and Fatima
- Mark and Fatima do not have any asthma or allergies.
- They live with their dog, a golden retriever named Treacle.
- Mark and Fatima have two children, Harry and Aydin. Neither of the children develop asthma or allergies.
Now imagine a research study involving the two families. The study finds that the children living in a pet-free home have asthma and allergies, whereas the children living with a dog at home do not have asthma and allergies. The results seem to speak for themselves: Pets prevent asthma. Or do they?
If there’s one thing I've learned from analysing these studies, it’s that correlation does not mean causation. Yes, there is a correlation between not having pets and children developing asthma and allergies. However, this doesn’t mean that living in a pet-free household caused asthma and allergies. In our example, Milo and Sorrell’s parents both had pet allergies and asthma. The fact that Milo and Sorrell developed pet-allergic asthma may well have been due to genetics rather than the absence of pets at home.
Whilst this is a simplified example, pet-allergic parents avoiding pets while their children being genetically more susceptible to allergies and asthma, is noted to be one of the main confounders in this field of research. One way to get around this confounder is to note children’s family history when they take part in this kind of research. Other major confounders are breastfeeding, parental smoking before or after birth, and lifestyle factors such as diet and exercise. This information can then be applied to the results, as it was done in the study by Pohlaben and the study by Lodge.
Study 5: Perinatal Pet Exposure, Faecal Microbiota, and Wheezy Bronchitis
In 2013, researchers Nermes and colleagues published a study that tackled the most prominent confounding variable a different way. Their study investigated perinatal pet exposure, gut flora, and diagnoses of wheezy bronchitis—a type of viral chest infection common in infants. Interestingly, they selected a sample of participants in which every single one had a family history of allergies or asthma. They found that at age two, none of the pet-exposed children had ever suffered from wheezy bronchitis. In the non-pet-exposed group, 15.3% had suffered from this condition, some more than once.
Results for Children With a Family History of Asthma or Allergies
Percentage who suffered wheezy bronchitis
Children without pets
Children with pets
According to the researchers, the children living with pets did not develop wheezy bronchitis because they had a greater number and a greater diversity of bacteria in their gut flora. This improved their immune system and helped protect them against wheezy bronchitis.
All in all, the evidence base suggests that having a pet as an infant can reduce sensitivity to airborne allergens. However, expert opinion varies on whether this protective effect is powerful enough to completely ward off the development of allergic asthma, especially in those that are genetically at risk. For children with a family history of allergies and asthma, having a pet may actually increase their chance of developing these conditions.
A clear consensus is difficult to find in the current literature, which is muddied by cohort studies and their associated confounding variables. Whilst a randomised, controlled trial (RCT) would eliminate these variables and yield more reliable results, it’s difficult to design such a study. After all, you can’t randomly give a family a dog without them knowing, and you can’t give them a placebo dog without them soon figuring out it’s not real.
The bottom line is that family pets bring many benefits. They teach children about caring and compassion, nurturing and empathy, responsibility and respect. Their presence is said to contribute to a child’s cognitive, emotional and social development. They will be a loyal, unquestioning companion to share secrets with and to gain comfort from when a child is scared, angry or upset. They will enrich the whole family’s lives with joy, fun and laughter. You can rely on your pets to do all of these things, but, given the current evidence, do not rely on them to prevent asthma.
This article is for informational purposes only. It is not intended to be used as medical or life advice. If you are considering owning a pet but have concerns about the health effects, consult your doctor.