In the 1890s, the story goes, a man by the name of William Radam became a millionaire by selling bottles labeled "Microbe Killer Number One." Unbeknownst to his customers, his concoction contained only water and a drop of wine—a potent recipe for snake oil, perhaps, but not an antibiotic. More than a century later, science and the marketplace have conspired to give us countless (albeit generally more effective) products for killing off germs. From antibacterial soaps and cleaners to antibacterial cutlery and even children's toys, the number of these products on the market has soared in recent years.
The urge for sterilized purity is understandable enough: Deaths caused by infections in the United States rose 58 percent between 1980 and 1992, microbes are developing antibiotic-resistant strains at a frightening rate, and news of outbreaks of Ebola, hanta virus, and flesh-eating strep infections—not to mention the more common E. Coli and salmonella—has sent us on a fearful cleaning spree, as we try to keep our lives as germ-free as possible. But, as Garry Hamilton explains in the British journal New Scientist (July 18, 1998), "today's squeaky clean world" could be making us ill.
According to an increasing number of scientists, our "growing separation from dirt and germs" may be behind the rapid rise in allergic diseases, such as asthma, and perhaps even autoimmune diseases, such as diabetes and rheumatoid arthritis. "Wherever you look," writes Hamilton, "allergic diseases seem to follow hard on the heels of wealth and modernization"; asthma, hay fever, and eczema are all on the rise, and doctors report seeing more children at a younger age developing insulin-dependent diabetes.
According to a new theory—dubbed the hygiene hypothesis—these trends are the result of our society's aversion to dirt and muck. "During most of evolution the immune system was bombarded with dirt and germs from the moment each newborn infant hit the cold light of day," Hamilton explains. Just as the brain cells of a baby need stimulation to make the right connections, the argument goes, the immune system needs proper stimulation to develop properly. According to the hygiene hypothesis, exposure to the microbes that live in dirt and grime helps the immune system defend against certain diseases, particularly asthma—which afflicts 14 million people in the United States, killing 5,000 every year.
In the case of asthma, however, the data seem clouded. Though some studies appear to support the hygiene hypothesis, there is an overwhelming volume of evidence that asthma is more of a problem in crowded, unsterile environments. According to Mindy Pennybacker in The Green Guide (July 1, 1998), "inner-city children are truly the canaries in the coal mine for this disease"; they are bombarded by allergens—cockroach parts, emissions from gasoline and coal combustion—that aggravate the condition. Pennybacker also points out, however, that asthma is "increasing among Americans of all incomes and races"—and the statistics she presents on inner-city cases show increases in hospitalizations for asthma, not increases in the appearance of the condition itself.
Clearly, the conditions of poverty aggravate asthma, but that fact alone does not disprove the hygiene hypothesis. While supporters of the hypothesis have yet to find indisputable epidemiological evidence of their claims, immunologists have discovered a mechanism within the immune system that jibes with their theory. At birth, we have a certain number of immune cells called Th cells, which are directed by our environment into one of two paths. Either they become Th1 cells, which instruct immune cells infected with bacteria to kill the intruder, or Th2 cells, which send out antibodies, triggering a chain of events that includes the runny nose and wheeziness that plague asthmatics and the allergy-prone. Th cells growing in a flask in laboratory experiments become Th1 cells when they're marinated with a chemical that our immune cells naturally release when under attack.
"In our mucky past, the theory goes, babies swarmed with bacteria and viruses, and this ensured [that] the balance was sufficiently weighted toward Th1 cells," Hamilton writes. "Remove those microbes from the picture, and the immune system is irrevocably pushed toward favoring the allergy-inducing Th2 response."
The most helpful microbes, some scientists argue, are those that lurk in the soil, beyond our increasingly hermetically sealed lives. "Mycobacteria live in soil, and pond and stream water, but not in our bodies, so our changing relationship with the environment is likely to have had a gigantic influence on our contact with them," Hamilton writes.
So sending our children out to make mud pies may soon be seen as preventive medicine.