Nowadays, more Americans have allergies that ever before. In fact, a whopping one-third of adults and 40% of children suffer from some kind of allergy, be it to pollen or a type of food or a specific chemical. But it wasn’t always this way. If you grew up in the 80s or 90s, like I did, you probably didn’t hear much about allergies. You probably weren’t familiar with the terms “EpiPen” or “anaphylactic shock.” And I bet your school didn’t have a peanut-free policy, either.

Things have changed dramatically in the last couple of decades. The number of kids with food allergies went up 18 percent from 1997 to 2007 with peanuts, tree nuts, milk, soy, wheat, shellfish, fish, and eggs being the most common offenders and causing a cumulative 90% of food allergies. The prevalence of allergic diseases, like eczema and asthma, have doubled or tripled during the past three decades in the industrialized world. And the list of allergens — from shellfish to latex — seems to be growing.

Scientists believe that the cause of this “allergy epidemic” has to do with the trillions of bacteria residing in our gut and shaping our immune systems. Our bodies are populated with bacteria, also called “microbes” or “flora”, from the moment we leave our mother’s wombs. Researchers say that these microbes play a vital role in training our immune systems to attack dangerous germs and to ignore harmless things like pet dander and dust.

If you’re wondering exactly how these bacterial microbes teach our immune system to work properly, you’re in good company. Scientists are still figuring it out.

What they do know is that there is a beneficial, symbiotic relationship between our immune cells and microflora populating our bodies. For example, scientists found that mice with bacteria-free intestines and lungs suffered from asthma and colitis. However, once they exposed them to a certain bacterial strain, effectively diversifying their microflora, their immune systems calmed down and their disease symptoms lessened.

So, why kids are developing allergies at skyrocketing rates?

So, why kids are developing allergies at skyrocketing rates? One prominent theory, also known as the “hygiene hypothesis,” suggests that it’s because our society is too clean. As a consequence, children aren’t getting exposed to enough of the beneficial microbes that train their immune systems to distinguish between friend and foe.

Think about it: thanks to modern sanitation measures, our water supply is decontaminated, our milk is pasteurized, and food products are sterilized. Then there are childhood vaccinations, which further shield our children’s immune systems from germs. Add in our obsession with hand-washing and anti-bacterial gels, and you’ll realize that despite the occasional e-coli or listeria outbreak, we’re actually a very sanitary society (even in the “grimy” inner city). While all these modern advances make our lives more pleasant, they may come with a cost.

So, what happens when you compare a modernized country like the U.S. with one that has poorer sanitation? As you might expect, people living in the developing world tend to have a greater diversity of gut bacteria and a much lower prevalence of allergies as a result. This is because members of these populations are chronically infected with various pathogens, like parasites and the Hepatitis A virus, which live in contaminated food and water supplies. Exposure to such germs early in life makes allergies a rare occurrence.

In addition to cleanliness, there are other interesting factors that can impact whether a child is exposed to good germs early on. One is the dramatic rise in C-section rates (which increased by 50 percent in the last 15 years in the U.S.). Because the birth canal is populated by a host of beneficial microbes, babies born by C-section miss this first dose of amazing bacteria from their mothers. As a consequence, they’re more likely to develop asthma and other allergies.

Then there’s antibiotic use: children given antibiotics in their first year are more allergy-prone more because these medications can kill off beneficial gut flora. And, you’ll love this one: gender may have an impact, too. Girls are more likely to be allergic than boys. Some scientists argue that this is because of societal norms, which dictate that girls should be held to a higher standard of cleanliness than boys. I bet this is a gender divide you haven’t heard of before!

Girls are more likely to be allergic than boys.

Finally, the Western diet may play a role in the allergy epidemic, as well. One study suggests that a vegetarian, low-sugar, and mostly unprocessed diet increases the diversity of flora in our guts, whereas the typical American diet of processed, high-fat, and high-sugar foods does the opposite. Nutrition-wise, this theory makes sense. Vegetables naturally contain lots of prebiotics, which act as food for beneficial gut bacteria.

Now for the good news: if you had a dog as an infant or if you were raised on a farm, then you’re in luck. In both cases, you were exposed to beneficial bacteria that are found on animal fur (which Fido collected during his walks), in manure, and in plain old dirt.

Now, before you go rolling around in the mud, remember that the jury is still out. Scientists are still exploring how the environment around us impacts our gut flora, and which germs are actually good for us. In the meantime, check out some of the cutting edge research being done in this field and get up close and personal with your own microbiome by having it sequenced and analyzed. How cool!

Angelika Schlanger, PhD, is a Yale-trained-researcher, Health Coach, blogger, food-system reformer, and mom to three healthy eaters (well, sometimes). She helps institutions, individuals, and families create a balanced wellness program that is tailored to their individual needs. Angelika enjoys concocting healthier versions of classic recipes, growing her own organic veggies, and taking long naps on the beach. Read her articles and tips at homehealthlove.com and follow her on Twitter @homehealthlove.

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