Good News About Kids and Germs

Biologist Rob Dunn makes connection between germs and Crohns

/ Author:  / Reviewed by: Joseph V. Madia, MD

It's a daily struggle to keep your kid away from germs, but it could be time to give up the fight. The more exposure he has to dirt and microorganisms, the healthier he might become.

The scientific support for playing in the dirt has been steadily growing into a pile of evidence.

Scientists believe that exposure to germs serves to “tune up” immune systems early in life, and prepares them to protect our bodies against mysterious immune diseases like Crohn's disease and multiple sclerosis.

Dr. Rob Dunn is a biologist at North Carolina State and a writer. In his book, The Wild Lives of Our Bodies, he explores the idea that our modern obsession with cleanliness, including our anti-bacterial soaps and disinfectant sprays, has wiped away our bodies' ability to fight off infection.

dailyRx asked Dunn how this hypothesis might explain Crohn's.

dailyRx: The cause of Crohn's disease is not known. What are some of the reasons why Crohn's disease is so mysterious?

Dr. Dunn: The immune system does two things: It helps to facilitate the survival of some beneficial species on and in our bodies, and it fights the bad ones.

In the wild west of our bodies, the immune system plays sheriff. At least that is what we tend to think of the immune system as doing. It is what it is "supposed" to do, to be our compass as we exercise a kind of ecological morality in discerning what we need from what might kill us.

In Crohn's disease, the immune system essentially decides that the body is one of the opponents. The rule of law is, if not entirely abandoned, shifted in such a way as to lead to terrible inflammation and other problems in the guts of the afflicted.

dailyRx: Crohn's disease has recently become much more common of a diagnosis. Why is it on the rise?

Dr. Dunn: No one can tell you for sure. But one thing seems clear: It is more on the rise in those places where we have more effectively gotten rid of our worms (and also improved public health conditions more generally); places, in other words, where it is now rare to walk through the feces of other people or to poop in the woods.

The worms seem to be part of the story, though clearly they are not the whole story.

dailyRx: What do the communities of germs that populate our bodies have to do with Crohn's?

Dr. Dunn: Ah, many things. For one, it now seems clear that if you have an autoimmune disease, such as Crohn's and you are infected with one of several potential worms (there are tens and tens of species that at least sometimes wind their way into humans) that the symptoms go away more often than they don't.

Conversely, for some other auto immune disorders, maybe most, when you remove worms those disorders become more likely. It seems that those worms play a role in either helping our bodies to develop or in "calming it down," though just how this is happening is a messy question with no clear answer.

That is one kind of "germ" effect, though worms are far too lovely and fascinating and complex and diverse to get called germs. In essence, this is the story of how public health infrastructure affects our immune systems by making it harder for worms to find us one toilet at a time.

The other kind of germ effect is the one typically talked about in the context of bacteria (or archaea). In that context the story is a bit different. With bacteria the idea tends to be that having a richness of bacterial species around in childhood helps "train"the immune system.

In this context, the best data relate to allergies rather than Crohn's disease and tend to suggest that kids exposed to more bacterial richness in farm settings are less likely to get allergies than those exposed to fewer kinds of bacteria in the city.

At least in lab animals, there is some evidence that these ideas might extend to Crohn's as well. In lab animals without microbes, Crohn's like symptoms can develop and if those animals are innoculated with microbes, the symptoms can be shown to largely go away.

But the story is far from well revealed, in part because the bacteria in our lives are so incredibly diverse. You have hundreds of species in your belly button and thousands in your house and just which ones our immune system might "need" or what aspects of them it might need is a ways from being understood.

dailyRx: Why might it be beneficial for kids to be exposed to germs early on, not just in terms of potentially avoiding Crohn's disease?

Dr. Dunn: Oh, I think it is good for kids to be exposed to lots of species in general. They should see birds. They should watch ants. They should be out in the wildness of life. Exposure to dirt and trees and bark and leaves and the textures, species, and feelings of being in the context in which we evolved are good in many ways.

Next time you are tempted to buy your niece a new toy, give her a rock and stick and tell her to make something. In doing so, she will connect with the way children have long played, but also connect with all sorts of bacteria. Those bacteria may help her stay healthy.

My gut sense (if you pardon the pun) and the literature seem to suggest as much. But more needs to be understood. We are, at the moment, conducting a study of the microbes in households across America right now to try to understand.

But the picture is one that needs many lenses. The living world is still mostly darkness in terms of our understanding and we continue to try to understand it with relatively weak lights.

As a biologist, that is fascinating, but the other reality is that this should worry you a little because most of what lives around you and most of what it is doing or failing to do to you is still totally unknown. It will be for a long time.

Recent Evidence

The idea that our lack of bugs and germs might weaken our immune system is not a new one. It appeared in the scientific literature back in 1989, and is dubbed the “hygiene hypothesis.”

A recent study published in the journal Science tested the theory on mice. A team of researchers led by Drs. Richard S. Blumberg and Dennis L. Kasper at Harvard Medical School compared a group of mice raised in a environment filled with bacteria to mice who grew up in a sterile environment.

They found that the germ-free mice were more likely to develop allergies, asthma, and autoimmune diseases like inflammatory bowel disease (IBD), than those who had wallowed in germs all their lives.

The effect could be seen by comparing the mice groups' killer T cells. Killer T cells are immune cells that fight infection – in normal bodies.

But in some of these germ-free mice, the killer T cells were over-active. They had turned on the body and attacked healthy tissue. That's what happens in diseases like Crohn's, asthma, and ulcerative colitis.

The researchers added that the time at which the mice were exposed played a big role in their immune system development. Exposure needs to happen early on in childhood.

Early exposure to germs seems to “teach” the body not to over-react in normal circumstances. It may be that germ-free bodies never learn what's normal and what's not.

That doesn't mean you should leave your child to play in environments you might call dangerous. But maybe it's okay if he plays outside without shoes, or has a healthy taste of dirt every once in a while.

Review Date: 
April 12, 2012