Do 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. My Informed Life figured it was time to get our claws in to the evidence-base.

According to the World Health Organisation in 2014, 235 million people worldwide suffer with asthma. It is the most common non-communicable (non-infectious) disease among children. The condition can be classified as either ‘atopic’, ‘non-atopic’ or ‘mixed’.

Atopic asthma

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, particles of an animal’s dander or feather dust. Cat-allergic asthma is actually an inflammatory response to a protein in cat saliva, coated on their fur as they wash themselves and wafted around the house as they moult. Euuuuwwwwww….

A white and tortoise-shell cat licking lying on the pavement licking its paw with a giant rough pink cat's tongue

Cat-allergic asthma is an inflammatory response to a protein in cat saliva

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

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 main part non-atopic asthma can be thought of as non-allergic asthma.

Mixed 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? 

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 from asthma and allergies, anyway. But how true is this actually?

Young boy playing in long grass with two dogs

Apparently, back in the day when young children ate mud, made dens and shared their dog’s bed, no one had any problems

Well, at My Informed Life we like nothing better than to doggedly sift out fact from fiction. Here’s the low-down from the scientific studies we 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. To take part in the research, new mothers were recruited from five different hospitals in Germany, between the years 1999 and 2000. Before heading home with their new bundle of joy the mothers completed a lifestyle questionnaire which 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, those with no family history of asthma or allergies (referred to as no parental atopy), and 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 when aged 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.

Children with no family history of asthma or allergies (no parental atopy)

 Living without a dog as an infant:  20.7% developed asthma or allergies
 Living with a dog as an infant:  11.8% developed asthma or allergies

In the group of children with no parental atopy it seems that all those playtimes with Rover had reduced allergies and asthma by almost a half.

Picture of a young boy hiding behind a white and ginger puppy's face

Pohlaben found that for children with no parental atopy, having a dog reduced the risk of asthma and allergies 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.

Children with a family history of asthma or allergies (with parental atopy):

 Living without a dog as an infant:  26.9% developed asthma or allergies
 Living with a dog as an infant:  34.9% developed asthma or allergies

In the group of children with parental atopy, Rover’s dogmatic presence around the home had increased allergies and asthma by almost one-and-a-third.

Picture of a Westie dog sat in a child’s pushchair

Pohlaben found that for children with parental atopy, having a dog increased the risk of asthma and allergies by almost one-and-a-third

In 2012, Lodrup Carlsen and colleagues published a meta-analysis (a study of studies) investigating whether pet ownership in infancy lead to asthma or allergies at school age. Data was pooled from 11 European studies and involved 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 asthma, allergic rhinitis (itchy sneezy snotty-nose symptoms) or sensitivity to airborne allergens.

Sensitivity to airborne allergens was found to be significantly less in the children who’d had pets, compared to those who hadn’t. But there was no such pattern for pets and childhood asthma. After looking at all the research the authors concluded that having a pet in infancy neither increased nor decreased a child’s risk of developing asthma; the study had failed to find any link at all.

Boy in colourful clothes outside in the sunshine with a parrot on his right shoulder

Lodrup Carlsen found that furry and feathered pets reduced sensitivity to airborne allergens but did not affect the risk of asthma

Also in 2012, Lodge and colleagues published a systematic review (another study of studies) of perinatal dog and cat exposure and risk of asthma. Data was collected from nine studies involving 6498 participants. Their findings echoed the findings of Pohlaben’s study; 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.

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.

It was found that atopic (allergic) asthma was far less prevalent in the group of children who’d lived with a cat, dog, rabbit or bird during infancy. The pet-owning group of children were 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.

A white and grey ferret running in the grass next to a toddler's feet

Collin found that pet ownership reduced a child’s risk of allergic asthma yet increased the risk of non-allergic asthma

Confounding variables

Clearly, the idea that ‘pets prevent asthma’ is more than just an old wives’ tale. Indeed, numerous scientific studies support the theory. However, not all researchers agree on the existence of, or the extent of, the protective effect of pets. The varying in the conclusions is perhaps because the evidence-base is dominated by cohort studies. That is, observational studies of people living their lives. Unfortunately for research, studies of people living their lives come with the baggage of many confounding variables. Consider 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.
Picture of a Mum and Dad lying on a big double bed with a five year old child and a small baby

Ben and Josie have pet allergies and asthma and live in a pet-free home. Their children Milo and Sorrell develop 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.
Picture of a happy family including two parents and two young boys playing on the lawn with their golden retriever dog

Mark and Fatima do not have allergies or asthma and live with their dog Treacle. Their children Harry and Aydin never develop any 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, it seems, speak for themselves: Pets prevent asthma. Or do they?

If there’s one thing we know at My Informed Life, it’s that correlation does not mean causation. Yes, there is a correlation between children not having pets, and those children developing asthma and allergies. But this doesn’t mean that it was living in a pet-free household that caused those 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 pet absence at home.

Whilst this is a simplified example, pet-allergic parents avoiding pets, and their children being genetically more susceptible to allergies and asthma, is noted to be one of the main confounders in this field of research. Other major confounders are breast-feeding, parental smoking before or after birth, and lifestyle factors such as diet and exercise.

One way to get around the pet-allergic parents avoiding pets confounder is to note children’s family history when they take part in this kind of research. This information can then be applied to the results, as it was in the study by Pohlaben and also the study by Lodge.

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. And interestingly, they selected a sample of participants where every single one had a family history of allergies or asthma. The study found that, at age two, none of the pet-exposed children had ever suffered with wheezy bronchitis. In the non-pet-exposed group, 15.3% had suffered with this condition, some more than once.

Children aged two with a family history of asthma or allergies (with parental atopy)

 Children without pets:  15.3% suffered wheezy bronchitis
 Children with pets:  0% suffered wheezy bronchitis

According to the researchers, the results arose because the infants who lived with pets had a greater number and a greater diversity of bacteria in their gut flora. This then improved their immune system to protect against wheezy bronchitis.

Conclusion

All in all the evidence-base does seem to suggest that having a pet as an infant can reduce sensitivity to airborne allergens. However, expert opinion varies on whether or not this protective effect is powerful enough to completely ward off the development of allergic asthma, especially in those that are genetically high at risk. Indeed, 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 evidence-base, which is muddied by cohort studies and their associated confounding variables. Whilst a randomised controlled trial (RCT) would regulate these variables and deliver a more reliable conclusion, it’s pretty hard 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.

A dog lying outside on a patio with two cuddly stuffed toy animals

Real pet or placebo pet: how long would it be before you figured out the difference?

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-base, do not rely on them to prevent asthma.


References

Collin SM, Granell R, Westgarth C, Murray J, Paul E, Sterne JAC and Henderson J (2014) ‘Pet ownership is associated with increased risk of non-atopic asthma and reduced risk of atopy in childhood: Findings from a UK birth cohort.’ Clinical and Experimental Allergy. 2014 pp. 1-11.Wiley [Online] DOI: 10.1111/cea.12380 (Last accessed 04th August 2015).

Lodge CJ, Allen KJ, Lowe AJ, Hill DJ, Hosking CS, Abramson MJ and Dharmagel SC (2012) ‘Perinatal cat and dog exposure and the risk of asthma and allergy in the urban environment: A systematic review of longitudinal studies.’ Clinical and Developmental Immunology. 2012 pp. 1-10. DOI: 10.1155/2012/176484 (Last accessed 04th April 2015).

Lodrup Carlsen K, Roll S, Carlsen K, Mowinckel P, Wijga AH, Brunekreef B, Torrent M, Roberts G, Arshad SH, Kull I, Kramer U, Von Berg A, Eller E, Host A, Kuehni C, Spycher B, Sunyer J, Chen CM, Reich A, Asarnoj A, Puig C, Herbarth O, Mahachie John JM, Van Steen K, Willich SN, Wahn U, Lau S and Keil T (2012) ‘Does pet ownership in infancy lead to asthma or allergy at school age?: Pooled analysis of individual participant data for 11 European birth cohorts.’ Plos One 7 (8), pp. 1-12. Available from: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0043214 (Last accessed 04th April 2015).

Nermes M, Niinivirta K, Nylund L, Laitinen K, Matomaki J, Salminen S and Isolauri E (2013) ‘Perinatal pet exposure, faecal microbiota, and wheezy bronchitis: Is there a connection?’ ISRN Allergy 2013 (Article ID 827934), pp. 1-6. Hindawi [Online]. Available from: http://www.hindawi.com/journals/isrn/2013/827934/ (Last accessed 04th April 25th October 2014).

Pohlabeln H, Jacobs S and Bohmann J (2007) ‘Exposure to pets and the risk of allergic symptoms during the first 2 years of life.’ Journal of Investigational Allergology and Clinical Immunology. 17 (5), pp. 302-308. Pubmed [Online]. Available from: http://www.ncbi.nlm.nih.gov/pubmed/17982922 (Last accessed 04th April 2015).

World Health Organisation (2014) Chronic respiratory diseases: Asthma [Online]. Available from: http://www.who.int/respiratory/asthma/en/ (Last accessed 04th April 2015).


Have you or has anyone you know had an experience with pets and allergies or asthma? Please comment on this article or start a discussion via a new thread. We would love to hear from you about your own experiences and research.

This article has 2 comments

  1. Sarah

    This is a very interesting article, especially seeing as in the Daily Mail a little while ago they had an article describing how pets DO reduce the risk of asthma! Goes to show you can’t always believe what you read.

  2. Abbie1980

    “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.” I love this. I’m sure some scientists SOMEWHERE could do, all in the name of research.

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