Luke Voytas is a pediatrician and author in Portland, Oregon. His posts combine research and common sense to help parents be calm and confident in raising their kids.

On Dirtiness

On Dirtiness

I like the word “dirty.” I’m comfortable with it. I’m kind of dirty right now. I get nervous when things are too clean. Once I didn’t shower for 15 days during a backpacking trip and was really dirty. It was great – kind of like having a shell. My house is usually dirty too, except for the rare spasms of cleaning when we are having people over. My kids? Well, I think I would call them “grubby” rather than dirty.

Dirtiness gets a bad rap, and I think it’s unfair. Until the past few decades, dirtiness has followed us wherever we’ve gone. And, of course, cleaning things up hasn’t been all that bad – our food is safer, we don’t live with the constant threat of cholera, and we probably smell better. But have we gone too far? Are we too clean now? The “hygiene hypothesis” theorizes that a lack of early exposure to dirt and parasites results in weaker immune systems and increased allergies. In fact, the CDC estimates that the rate of food allergies increased by 50% between 1997 and 2011. (1) Do our kids crawl out of infancy on gleaming floors with mushy immune systems?

There’s a growing body of evidence that this may be the case. Consistently, kids who grow up in dirtier environments seem to have less allergic disease as they get older. In a 2011 study, researchers performed allergy testing on hundreds of 18 year-olds who had been followed in an allergy study since birth. Those who had had a dog or cat at home during their first year of life had only about half the risk of being allergic to dogs or cats at age 18. (2)

A large 2017 study shed some light on how having pets at home might reduce the risk of allergies. (3) Researchers found that having furry friends in the household during pregnancy and after birth increased the amount of two types of good bacteria (Oscillospira and Ruminococcus) in babies’ intestines at 3-4 months. Higher levels of these bacteria have been shown to reduce the risk of allergies and even obesity as kids get older.

An awesome study from Sweden even found that at ages 7-8, kids in households that usually handwash their dishes had a lower rate of allergies than kids whose families used dishwashers (which presumably do a better job of removing dirty stuff). (4)

Finally, a 2015 study (also performed by those zany Swedes) looked at how parents cleaned off their kids’ pacifiers when they fell on the floor. (5) The researchers found that kids whose parents cleaned their pacifier by sucking on it themselves had less asthma and eczema as toddlers than those whose parents cleaned the pacifiers in more dignified ways.

So what’s the takeaway? A little dirt and exposure can go a long way to a healthier kid. So maybe don’t go so crazy with the cleaning, feel good about your messy pet, and give your toddler a little more free reign to pick things out of the carpet and see how they taste. And to my amazing allergy-free children, whose feet are blackened from going barefoot in their own home, you’re welcome.

1. Trends in allergic conditions among children: United States, 1997-2011. Jackson KD et al. NCHS Data Brief, no. 121; May 2013. https://ncbi.nlm.nih.gov/pubmed/23742874.

2. Lifetime dog and cat exposure and dog- and cat-specific sensitization at age 18 years. Wegienka G et al. Clin Exp Allergy. 2011 Jul;41(7):979-86. doi: 10.1111/j.1365-2222.2011.03747.x.

3. Exposure to household furry pets influences the gut microbiota of infants at 3-4 months following various birth scenarios. Tun HM et al. Microbiome. 2017; 5:40. https://doi.org/10.1186/s40168-017-0254-x.

4. Allergy in children in hand versus machine dishwashing. Hesselmar B et al. Pediatrics. 2015 Mar;135(3):e590-7. doi: 10.1542/peds.2014-2968.

5. Pacifier cleaning practices and risk of allergy development. Hesselmar B et al. Pediatrics. 2013 Jun;131(6):e1829-37. doi: 10.1542/peds.2012-3345.

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