Asthma and the Hygiene Hypothesis


Quick—what’s the first thing you think of when I say “bacteria?”

If it’s, “Bacteria, ick! Must wash hands,” you would be wrong on two counts:

  1. While some bacteria are indeed icky, even dangerous, our health is hugely dependent on “good,” or “friendly” bacteria, called probiotics, that live in our gut, or biome.
  2. Recent research is getting us close to a medical certainty that too much washing of hands and other “anti-ick” activities can be extremely health-negative. This counterintuitive notion is showing up in studies of asthma, in particular.

Good health takes guts

We all have trillions of healthy bacterial friends in our biome. They are so present, and so important, that some call them, collectively, a “forgotten organ.”

Like the cells in all of our true organs, our bacteria are constantly active. Job one? Our immune systems. Our biome is where at least 70 percent (and I think more) of our immune functions are orchestrated. Each bacterium has a specialized role: helping to transmit signals from body to brain, to digest our food, to identify and neutralize unwelcome bad bacteria and other intruders. Every action and interaction in our body has a pack of good bacteria helping to make it happen.

Just in: our lungs are loaded

We now know that there’s a lot more bacterial action in our lungs and other bronchial sites, than we knew.

There’s so much action, in fact, that our lungs and bronchial sites have earned their own name—the bronchial microbiome—a specialized partner that works with the overall “parent” biome.

And we now know there is a link between asthma and:

  • The bronchial microbiome’s unique makeup of specialist bacteria
  • How those bacteria respond to various internal and environmental stimuli
  • How giving antibiotics in the first year of life means an increased likelihood of asthma later in life

Overdoing “clean”

Here in the US, rates of asthma have tripled over the last 30 years.

But in the developing world, asthma is rare. And children studied in some of those regions have very different microbiomes than children in the so-called “developed” world.

Why? Our DNA isn’t different enough to explain this huge disparity.

It’s simple—and ironic.

When kids are exposed to bacteria, viruses, and parasites—even some that make them sick—their immune systems learn how to tell the difference between good guys it should leave alone and bad guys it should attack. This is an essential first step toward building immunity to the myriad naturally occurring pathogens we encounter every day. And the sooner this happens, the better. Our immune system is at its most adaptable in infancy and early childhood.

One Swedish researcher has concluded that our “anti-ick” practices indeed play a significant role here. Our hand sanitizers, air filters, anti-microbial cleaners, and disinfectants and so on strip the environment of the bad bacteria.

But our good bacteria must encounter them to learn how to defend against them.


  • Children living in super-clean, “anti-ick” environments don’t get that important immune system “training”
  • They are known to be at higher risk of developing asthma and allergies than children raised in a more natural setting.

There’s no “standard set” of good bacteria. But one study in Pakistan found that infants there had “typical” gut bacteria in place—a presumed starter set of sorts—earlier in life than infants in Sweden. This delay is thought to prevent the immune system from learning that antigens like pollen, cat dander, and certain foods are harmless—not to be attacked as allergens.

The kids, in effect, are left with a susceptibility to allergies that don’t have to be allergies.

That’s one piece of the puzzle.

Overmedicating with antibiotics

Our tragic increase in asthma and allergies tracks right along with the widespread use and overuse of antibiotics. As I’ve written before, antibiotics are a biome disaster, wiping out our good bacteria—70 percent of it and more—along with the bad.

So while we over-clean and strip our external environment of vital stimuli, we overkill and strip our biome of vital defenses.

A very dangerous one-two punch.

What we can do: prevention and intervention

There should be no question as to where all of these findings take us.

But there is one: Knowing that we can over-clean, to the detriment of our children, how do we ratchet our practices back? How clean is clean enough?

Start by recognizing that a home, maintained for your family members with normal immune systems, should not be cleaned in the same way as a hospital, full of people with weakened immune systems from illness or surgery. You should choose natural cleaners, like soap and water, vinegar and baking soda, and good old-fashioned elbow grease, instead of harsh, chemical, antibacterial products.

Become anti-antibiotic

I expect that in the ideal world we’re all working toward, there will one day be a menu of necessary good bacteria, tailored for every child’s biome and for every external environment, and the means to ensure that every child is provided those bacteria in a controlled way.

It could be as simple as a customized probiotic supplement.

Until that day … let’s give our biomes the care they deserve.

We have to make all doctors and all patients aware that there are much better alternatives to antibiotics—diet and lifestyle changes that strengthen our biomes and microbiomes instead of compromising them. If you have asthma or allergies, I urge you to find a doctor who’s seen the light and will help you make those lifestyle changes. If you have an infant, by all means say ‘no’ to antibiotics.

And what can we do to strengthen our bronchial microbiome? Simple: strengthen the parent biome. People who live together exchange bacteria frequently.

For this task and for overall good health there are nature’s magnificent probiotics—the good bacteria found in yogurt and other fermented foods and drinks. Make them part of your daily diet. You have a world of sources at your fingertips, from yogurt to kim chi to cider vinegar to red wine. If you take a probiotic supplement, look for one with at least 10 billion CFUs.

As always, make sure that whatever you buy is local, organic, and humanely raised.


Last Updated: August 16, 2018
Originally Published: October 28, 2015