A few years ago, my mom and I were watching old videos that she took of me as a baby. One featured infant-me crouched behind my dog’s water bowl and joyfully splashing my hands in the water, as if in a pool. My mom sat behind the camera giggling and cooing to me. Older me, who understood all the potential germs present in the dog’s stagnant water bowl, was horrified: “Why did you stand there let me do that?!” My mom, not ready to have her parenting methods questioned, responded “Look, you were having so much fun, and it’s probably made your immune system stronger.”

I’ve often wondered how much of an impact being around a dog at such an early age has affected my health and overall wellbeing. When I was one, my parents adopted a Bullmastiff puppy, Greta, who rapidly eclipsed me in size, growing to be 120 pounds. For the 12 years of her life, we were inseparable. She’d always tolerate me sitting directly on her, and she’d love to cuddle for hours in the morning. But she was frequently “gross.” Greta liked to lick faces and after drinking water, her slobber would always drip off her droopy mouth onto the floor. She could never go into the backyard unsupervised since she’d eat her own poop.

Our love of dogs often clashes with contemporary expectations of cleanliness and hygiene. Some dog owners are more sensitive to the innate “dirtiness” of dogs than others and commit to more rigorous cleaning routines and frequent bathing of their furry companions. Increasingly, however, the long-term benefits of hygiene have been questioned by scientists, particularly in early childhood development. Throughout childhood, our bodies are continuously exposed to many microbes. Sometimes, these germs infect us, forcing a child who developed symptoms of the common cold home from kindergarten. Others, our immune system finds them harmless and learns to tolerate their existence. It’s key that this exposure happens early in life, when our immune system is more tolerant to foreign invaders. As we mature, our immune systems more often launch an inflammatory response to a benign microbe just because it does not recognize it. 

Dogs, with all their slobber and dirt, host loads of microorganisms and viruses. Some of these do pose a threat to humans: zoonotic like rabies or bacterial disease such as salmonella. However, modern medical care and vaccinations have alleviated many of the risks of pathogens spreading from dog to owner. Now, dogs may help regulate our immune systems further, especially in early childhood, by reducing the cleanliness of our households. 

Many studies on the effects of early-life dog (and cat) ownership have focused on “atopic” diseases such as eczema, asthma, and food allergies, which all are hypothesized to result from our immune systems launching an inflammatory response against something that does not pose a threat. In most studies¹, my mom’s efforts to prime my immune system via a doggy water bowl holds up. A meta-analysis² from 2013 found a 25% decrease in atopic disease for children exposed to dogs (but failed to find the same for cats). However, in some studies the effects are more complicated. A study³ from 2022 of more than 77,000 children from the EU discovered no association between pet ownership and asthma, and instead observed that atopic health risks increased for those who have a pet allergy and owned a pet. 

These mixed results may result from inconsistent ways of defining pet exposure. Studies differ in how long people have to be around animals for something to count as an “exposure.” Testing for atopic disease also varies between studies, with some only accounting for a certain type of disease or ignoring severity. But overall, with the exception of those who develop pet allergies, dogs mostly don’t seem to do harm to our immune system early in childhood, and very well may help. 

Even so, early-childhood pet ownership is associated with a myriad of other health benefits, particularly psychological ones. Indeed, a 2020 study⁴ found that recreation and play with a dog during pre-school was associated with a decrease in peer problems and increase in prosocial behavior, a pattern that has been backed up by many other pediatric studies⁵.

Anecdotally, I can say that having Greta as a pet in early childhood definitely taught me prosocial skills, in particular forgiveness. The day after my birthday, all 120-pounds of her leapt up on the counter to eat what remained of my cake. In a rage, I promised to not pet her for the rest of the day. Though when I came home from school that day and was greeted by her slow tail wag and black glossy eyes, I broke my promise and pet her sweet wrinkled forehead. Perhaps Greta just wanted to share the cake, all spread out across the floor, although I think that would’ve been a step too far for my immune system. 

1. Hesselmar, et al. (1999). Does early exposure to cat or dog protect against later allergy development? Clinical & Experimental Allergy, 29(5), 611–617. https://doi.org/10.1046/j.1365-2222.1999.00534.x
2. Pelucchi, C., et al. (2013). Pet exposure and risk of atopic dermatitis at the pediatric age: a meta-analysis of birth cohort studies. The Journal of Allergy and Clinical Immunology, 132(3), 616-622. https://doi.org/10.1016/j.jaci.2013.04.009
3. Pinot de Moira, A., 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
4. Wenden, E. J., et al. (2020). The relationship between dog ownership, dog play, family dog walking, and pre-schooler social–emotional development: findings from the PLAYCE observational study. Pediatric Research, 89(4), 1–7. https://doi.org/10.1038/s41390-020-1007-2
5. Minatoya, M., et al. (2021). Association between Early Life Child Development and Family Dog Ownership: A Prospective Birth Cohort Study of the Japan Environment and Children’s Study. International Journal of Environmental Research and Public Health, 18(13), 7082. https://doi.org/10.3390/ijerph18137082