One suggested explanation for the increased incidence of food and other allergy is the hygiene hypothesis.
This hypothesis proposes that kids who grow up in more sanitary environments are at increased risk for developing allergies. The heightened risk is owed to getting less exposure to microorganisms that stimulate and strengthen the immune system.
Although the hygiene hypothesis is still far from fact, there are plenty of scientific thoughts and data behind it:
Several lab mice were exposed to a bacterium called Mycoplasma pneumoniae, while a second group of mice were not. All the mice were then made allergic to an egg protein. After two weeks, the mice exposed to the bacterium had milder allergic reactions to the egg protein than the unexposed group.
A 2012 report made by the American College of Allergy, Asthma, and Immunology revealed there is a higher rate of childhood peanut allergy in wealthier families (kids aged one through nine). The researchers suggested the hygiene hypothesis as an explanation for their findings.
Research data indicate that kids who grow up around livestock and pets (dogs, cats) develop fewer allergies. It seems the harmless bacteria that thrive in dirt and dung actually signal our immune system to release inflammation-calming substances.
Some evidence for the hygiene hypothesis is anecdotal. Immigrants who come to the U.S. from Nigeria - where public sanitation is lacking - call allergies the “citizenship disease.” It seems that their allergies develop about three to five years after moving to the U.S. - about the time it takes to qualify for citizenship.
Germs and the Immune System
Beside the research and reports supporting the hygiene hypothesis, scientists also have a reasonable explanation for how highly sanitary conditions might alter the behavior of our immune system.
Our body is designed with two immune system pathways. The Th1 pathway uses small IgG antibodies to fight bacterial pathogens. The Th2 pathway releases the larger, and more inflammatory IgE antibodies to destroy unwanted parasites. People with allergies have immune systems that are biased toward the Th2 response.
It’s possible that a lack of exposure to microorganisms early in life disrupts the balanced development of the Th1 and Th2 pathways. This unbalance might allow excessive Th2 (IgE) reactions to what should be harmless proteins, such as those in eggs and nuts.
Though unsanitary living conditions come with their own set of nasty health concerns, a high rate of allergy isn’t one of them. However, if the hygiene hypothesis proves to be valid, there is no point in berating ourselves for becoming increasingly sanitary. We can instead acknowledge that even good things sometimes have unforeseen consequences—and maybe invite a little more dirt back into our lives.