The Dirty Truth About Kids’ Health: Microbiologist Brett Finlay on What We Get Wrong About Cleanliness

“The idea that the only good microbe is a dead microbe—that we’ve got to change.”

Dr. B. Brett Finlay is an award-winning microbiologist, the Peter Wall Distinguished Professor at the University of British Columbia, and the Director of the SARS Accelerated Vaccine Initiative. His most recent book, Let Them Eat Dirt: Saving Your Child from an Oversanitized World, was coauthored with Marie-Claire Arrieta and uses biological research to argue for an end to hyper-cleanliness. In this Heleo Conversation, Brett talks with Heleo’s Editorial Director Panio Gianopoulos about the difference between hygiene and cleanliness, how bacteria affect all parts of our lives, and why, microbially, dogs still count as man’s best friend.

Panio: In Let Them Eat Dirt, you argue that when it comes to hygiene, we’ve swung too far in the other direction. Clean is good, but too clean is problematic and it’s leading to things like higher rates of obesity and diabetes and asthma in children.

Brett: Yes, we’ve done a terrific job decreasing infectious diseases—the rates have plummeted, we’ve doubled our lifespan—but I don’t think any of us saw the unintended consequences. We had no idea these microbes were actually doing something useful for us, and with our quest to get rid of the bad germs, we’re also clearing out the good microbes. And the other thing is that it seems to have the most effect in early life and kids.

Panio: As a parent of three, I’ve been through that stage many times when little kids are putting everything in their mouths, like pennies and rocks. Is the idea that that’s a natural part of immunity building and you should just let them suck on the dirty lollipop they find on the ground? Where do you draw the line?

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Brett: If you picked up a handful of dirt a 100 years ago versus now, you’d be a lot safer now—we don’t have smallpox and polio and cholera and dysentery. If it’s just a pebble outside, it’s probably fine. I jokingly say that licking the floor in your own house is fine but licking the floor in the subway station is probably not a good idea. Playing in the sandbox is fine, unless it’s full of cat feces which can cause parasitic disease. You’ve got to balance it.

I’ve watched people slap kids’ hands when they have a stick in their mouth and then wipe them off with hand sanitizer. We have to ease off a bit.

Panio: A friend recently had a baby and as I walked in the front door I was handed an antibacterial wipe to wash my hands. I was like, “Whoa, I don’t even know if I’m going to hold the baby, but okay.” There was an immediate wipedown in effect.

“Just throw the hand sanitizer out. There’s no studies to show it actually does any good, and it probably does a lot more bad by getting rid of all these microbes.”

Brett: Our advice is that if you want to do the best thing for your kids, trying to be too clean is no longer the best thing. Studies show that if a kid’s pacifier falls on the ground and you either wash it off or put it in your own mouth before putting it back in the kid’s mouth—if you put it in your own mouth that decreases the kids’ rates of asthma and obesity, as opposed to washing it off. So just throw the hand sanitizer out. There’s no studies to show it actually does any good, and it probably does a lot more bad by getting rid of all these microbes.

Use soap and water before dinner and after the washroom, and if you’re in an infectious environment, like in a daycare, where there’s kids all around that are sick. There’s no studies to show that getting sick actually improves you, so you don’t need to have all these childhood infections. You can invoke the hygiene model if it’s risky there, but in a normal day-to-day circumstances, it’s probably not, so don’t bother.

Panio: I have a question about dirt itself. You mention in the book that if we saw a picture of an infected wound covered with dirt, we’d be disgusted by the whole thing but in fact, the dirt isn’t a threat, it’s just that it’s infected. It simply looks unclean. What is the difference between cleanliness and hygiene?

Brett: Bottom line is you can go and chew on dirt, generally speaking, it won’t hurt you, kids do it all the time. We mix up cleanliness with hygiene; we think they’re synonymous but they actually aren’t. Hygiene is encountering substances that have a high chance of having an infectious agent in them. Dirt doesn’t really have much infectious agents in it. I think you should look at whatever your kid is thinking of touching and say, “What is the chance that contains an infectious agent?” and if it is high, then you want to evoke hygiene practice. If it isn’t, like chewing on a leaf or something, that’s extremely low risk of having any pathogen on it and it’s fine.

Panio: It’s funny because there are so many scare stories about dirty things. I remember a news story where a lab found 3,000 types of bacteria on the surface of a dollar bill in New York. But it turned out those 3,000 don’t actually do anything that bad – at worst, they caused acne or something. But you hear these big numbers when someone puts something under a microscope, that it’s teeming with bacteria, and a horror hits you.

Brett: We just assume that any microbe is bad because it’s a microbe, and we’ve got to re-think that because we know that’s not true anymore. My daughter actually did a science fair project where she collected coins from the local grocery store as well as the hospital gift shop and then we compared the microbes. What we found was the number of microbes that are anti-microbial resistant was quite a bit higher on the coins from the hospital than if you went to the local grocery store. In a sense, there are some hygiene issues because antibiotic resistance is much higher in hospitals and you’re acquiring those microbes, which are not as good for you because they’re resistant to anti-microbes.

The idea that the only good microbe is a dead microbe—that we’ve got to change. I agree that germs are bad and they do cause disease and we need to get rid of them, but we’ve actually done a really good job of getting rid of most germs. When you look at the top 10 reasons why you’re going to die in the U.S., there’s only one that’s infectious, that’s #8: influenza pneumonia. Yet 9 of the other 10 reasons we now know are linked to microbes. Dementia, obesity, strokes, heart attacks, these all have beneficial microbe components to them that we didn’t even know about before. That’s why I’m on this campaign. We’ve got to rethink germs and microbes and realize that they’re just a part of our normal being. The world’s coated in a veneer of feces and it’s full of microbes, that’s just natural and we know it evolutionarily. We came from microbes originally and they’ve been with us all our life, and now we’re suddenly taking that part of the equation out of our lives, so we’re seeing the results.

Panio: Sometimes when I hear about the trillions of microbes I think we’ve got the metaphor wrong. We think we’re the ocean but we’re a few tiny plankton in an ocean of microbes.

Brett: Yeah, and we’ve kind of ignored them. During my career—I’ve worked on infectious diseases all my life—I was on this campaign, just like everyone, to get rid of these bad microbes. It was a stunning turn for me, even as a microbiologist, to suddenly start contemplating that some of these microbes might be beneficial. We’ve known since 1683 when van Leeuwenhoek looked inside his mouth with the first microscope and saw microbes, but we just ignored them, right? We have to do a major re-think. We’re all caught unaware on this.

Panio: Are you finding culturally that this idea of yours is running into a lot of pushback?

Brett: I’ll be honest, I’m very surprised at the warm reception it’s getting publicly. People say “Yeah, it makes sense. My grandmother used to say eat dirt,” that kind of thing. Where it’s going to take a little longer to get entrenched is in the medical profession. I’ve done pediatric seminars and the pediatricians think it’s fascinating but they have always been trained to use antibiotics to kill microbes, we have to keep our kids clean in hospitals—which you do, but that’s the hygiene aspect of it. Studies are starting to come out showing that antibiotic use early in life is not good, and even pediatricians are now saying, if a kid has an ear infection, let’s wait 24 hours and give them painkillers and see whether they really need to be treated, it might be viral, so maybe we don’t need to use antibiotics so much. It’s coming.

I’m not saying you have to smear dirt all over hospitals. There’s good bugs, there’s bad bugs, and we’re starting to know them. We just have to learn how to differentiate them.

Panio: I was relieved to see that pets are okay. Specifically, dogs are okay.

“Having a dog early in life decreases your chance of asthma and allergies by 20%. It’s because of all these microbes that he rolls around in the yard and then comes running back in and licks all over the kid.”

Brett: Dogs are okay. That’s interesting because if you go back a few years, if you were potentially asthmatic, they would say don’t get a pet because pets have allergens. Now it’s a 180 degree turn: we realize that having a dog early in life decreases your chance of asthma and allergies by 20%. It’s because of all these microbes that he rolls around in the yard and then comes running back in and licks all over the kid.

For the cat lovers, there’s no data either way. I think cats mostly sit in the corner, and they’re not licking the kid a lot. They don’t go out as much as dogs either. I looked up turtles and all these other animals but I couldn’t find anything. The only pet data is dogs being beneficial early in life.

Panio: You’ve mentioned that going outside is really good for us, that kids should play outside, and while that intuitively does seem correct, what if you’re living in a city? I mean, Grand Central? That’s where you get sick. Is the idea that you want to go outside but only where there’s not a lot of people?

Brett: You want to go outside where there’s microbes, ideally not infectious. So what do you advise a person that lives in central Manhattan on the 22nd floor? Do you want the kid crawling around on the street just outside the apartment tower? I think all of us recoil at that thought. We don’t know; what we do know is that living in the cities, all in the same place, eating the same thing, and basically secreting all the same microbes, our microbes are getting less and less diverse and more homogeneous.

There’s this idea, called the disappearing microbe hypothesis, that maybe these microbes are actually endangered species and each generation, as we’re getting cleaner and cleaner, we’re getting fewer and fewer microbes and how do we go back to get our great-grandparents’ microbes? This is a puzzle; we don’t know. Can you even fix it by other interventions such as taking particular mixes of probiotics or eating whole fermented foods?

I think diet plays a major role and that’s one thing we can control. Study after study shows that eating fruits, nuts, legumes, and high fiber—these are what are actually feeding the microbes. If you’re eating white sugars and white flour, that is already pre-digested and your body sucks it out in the small intestine and ironically, even though you’re eating, you’re actually starving the microbes which are further down in the large intestine. When you look at people that have these diets, especially obese people, they’re lacking in microbe diversity because they’re not feeding them, in a sense.

That’s one thing that you can do, that anyone can do: eat a very diverse diet of all these things that your Mom told you was healthy. There’s double the reason now, it’s not just that you’re getting your vitamins and nutrients, you’re feeding your microbes.

Panio: What about the connection between microbes and mental health? That seems to be in the news a lot.

“You can actually transfer that depression, anxiety, or stress just by shifting the microbes, which is really stunning.”

Brett: Yeah, that’s a hot topic. The data’s becoming quite strong for depression, anxiety, and stress. You can take a depressed, anxious, or stressed mouse and do a fecal transfer to normal animals. You can actually transfer that depression, anxiety, or stress just by shifting the microbes, which is really stunning. Then there are some really neat studies coming out of the UK now that, basically, the more courses of antibiotics you take, the higher your rates of anxiety and depression.

We did spend a bit of time in the book about autism because we felt we had to address it, and that’s a tricky one. As of right now, we cannot say that microbes cause autism, and that would be dangerous to say, but we can say there’s an awful lot of one-offs where a kid is fine and if they take antibiotics, they become autistic and then the mother convinces someone to do a fecal transfer which then decreases the symptoms. We actually tell one of those stories in the book. What we’re trying to say is that even diseases, such as autism, we know that autistic kids have different microbes in their gut. But they also eat differently and that’s just maybe it.

We just don’t know yet, but five years ago, who would have thought that microbes could be involved in brain diseases? I think in the next few years we’ll have very good answers. The whole gut-brain thing, that’s the hottest area, even in adults with depression and Alzheimer’s and Parkinson’s. Did you know brushing your teeth three times a day gives you a 50% decrease in your chance for dementia?

Panio: Wow.

Brett: It makes sense because if you have inflamed gums, then all these microbial components seep through, which causes inflammation in the body, and it’s this chronic inflammation that’s basically highly responsible for dementia. There’s a study in Denmark where they were cutting the vagus nerve, which runs to the gut from the brain—they actually were cutting it for another reason—but they looked years later and the people who’d had this nerve cut had far lower rates of Parkinson’s than those that didn’t have the nerve cut. It was a big number study too, so now we’re starting to think that Parkinson’s, which people think of as a brain disease, actually starts in the gut, there are microbial links to it, and then it goes to the brain.

It’s really upending things. I go to neurology meetings now and they want to know all about microbes, which is gratifying as a microbiologist but it’s terrifying as a neurobiologist. What do they work on, what do they do? It’s a very exciting area but a lot of the answers are not there yet.

This conversation has been edited and condensed.