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What Causes Food Allergies? The Smoking Gun.

I've always thought the hygiene theory, at least as most people interpret it, was pretty stupid.

Supposedly, the story goes, our immune system is bored and therefore misbehaves. Like a kid in the classroom watching the clock, it focuses on the wrong things because it doesn't have enough stimulation (illnesses and germs) to keep it busy.

Keep in mind that this is the same immune system that has evolved over 100,000 years of humanity. Surely in that time, some of our ancestors experienced periods of relative boringness, immunologically-speaking.

But there's another way to interpret the hygiene hypothesis, one I've mentioned before in my blog. Instead of theorizing that the immune system is bored, some scientists believe the immune system is missing a key component as a result of our overzealous hygiene.


People are not singletons. We are a conglomeration of organisms, including many bacteria  100 trillion of them, to be more or less exact. The purpose of the 5-year Human Microbiome Project (HMP) has been to catalog the bacteria a healthy gut contains.

The project has its challenges. Foremost among these is that bacteria often do not even grow outside the gut. Medical catalogs contains literally thousands of options that scientists can use to grow various bacteria. Some bacterial require solutions that are something like soup. Others grow only in blood. The odds are very good that many of the bacteria we'd be interested in knowing about are simply not growing in the lab for the HMP.

My daughter had one of these
cuties in her room when she
was small. Yes, we're total nerds.
But there's something else to consider. In the early 90's, hospitals started having a big issue. Patients were coming down with a nasty bug called MRSA  — methicillin-resistant staphylococcus aureus. You may be more familiar with it by its media name: flesh-eating bacteria. MRSA was a huge problem because hospitals didn't have many antibiotics that would treat it. More concerning, the bug was becoming endemic in hospitals and the cause was soon apparent: healthcare professionals were moving from patient to patient and spreading the bug. In some cases, healthcare professionals were actually colonized by MRSA. The solution? Enforce strict hand-washing routines using hand soaps that contained agents strong enough to kill MRSA.

The primary additive used? Triclosan.

How do I know all this? I started my career in healthcare marketing in 1988, the same year a very well-known medical hand soap brand was first launched. Over the years, I did quite a bit of the marketing and advertising for the brand, including hand-care hygiene continuing education and scientific effectiveness studies.

I had the soap in my office bathroom. In my house. Always.

Today, I saw for the first time the study I've been dreading: a direct tie between triclosan levels in children and allergic diseaseFor years, I've suspected the tie between antibiotics and a loss of gut bacterial diversity, but this is the first study that shows the direct link. It makes so much sense! 

"But I didn't work in healthcare," you say, "so this can't be the answer for my family." Not happy news for you: triclosan is literally in every room of your house.

There have been several tantalizing studies over the years that have hinted at an association:

  • Winter babies have more food allergies. The hypothesis put forth in the study is that food allergies are tied to gestation that occurs during tree pollen season, yet another study demonstrated that sensitization does not occur in utero. Could it be as simple as winter babies are in inside more, thereby exposed to a greater level of environmental contaminants?
  • People in developed countries have more food allergies. Except in Japan. Despite having a very hygiene-centric culture, Japan has a low level of food allergies. They also ban the use of  triclosan in cosmetics and other products.
Triclosan is about as altering a substance as you can imagine for bacteria. Think of a field after a wildfire goes through. Once the ecosystem that grew up slowly and harmoniously is wiped out, new species colonize the field. They're the hardy ones, the ones that can find root in inhospitable soil. The weeds. You can bet that once triclosan moves through the body, the bacteria left to grow will not be the microbial version of daisies.

What else contains triclosan? A whole lot

"Where else did the study focus?" you ask. (Yes, I know you're sick of links and studies by now and probably sick of this blog post...but hang with it.)

The other chemicals the study cited were propyl and butyl parabens. I didn't work hand-in-hand with these chemicals (excuse the pun), but Wikipedia is my friend. The second sentence jumped out at me: 

It is used as an antimicrobial preservative in cosmetics such as eye shadow, foundation, sunscreen, facial moisturizer and skin anti-aging treatment. 

If you read through, the Wikipedia author does not seem overly concerned about ingested parabens, as they apparently metabolize pretty quickly. However, parabens are a major component of baby products that are absorbed through the skin. We've been literally dousing our kids in parabens from the day they were born.

Why do I find this so theory so compelling? 
  • The timing fits. There have been many other causal agents proposed to explain the sudden rise in food allergies, but none of them fit the early 90's timeline needed to explain the explosion of allergies right around 1993-95.
  • The weird, outlier research fits. What other explanation covers the Vitamin D link, the redesigned nursery link (which also explains why higher household education might be associated with allergies - simply more money to redecorate), the tie between allergies and developed countries (except Japan), even winter babies. 
  • There's the start of an explanation for mechanism. Scientists are starting to explore how gut bacteria and the gut lining "talk" to each other. Research seems to show that the gut mucosal layer can actually become more permeable in the presence or absence of key bacteria, and that's one possible area where food allergy sensitization might occur. 
I may read this whole thing tomorrow and think "Nah!" But today, it makes sense to me and the research comes together in a way it hasn't for other theories. 

One thing I did do a couple years back was to start watching the products I bring into my house. I am by no means an environmentalist! (I didn't even know until I wrote this blog post that the EPA is reviewing triclosan.) However, going back to just plain soaps without antimicrobials seemed a prudent move. We also think a lot more than we used to about our sunscreen and other products that are absorbed by the skin.

In the meantime, I'm sure scientists will be busy comparing existing caches of food-allergic cohort samples to see whether the triclosan data hold up over a larger population.

Honestly, I hope it does. No one wants to look down the barrel of a smoking gun...but it's much worse to know there's been a shooting victim and have no idea where the bullet came from.

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