We all know people who go to extraordinary lengths never to shake hands or touch a tap in a public washroom, and whose cupboards are filled with antibacterial soaps. Inventions that address their fears are multiplying. One new product, a plastic box to be installed above the doorknob in a public toilet, sprays a disinfectant mist every fifteen minutes. Another, the Sanitgrasp, replaces traditional door pulls in restaurants and other public places with a big U-shaped object that allows the door to be opened by a forearm.
The list of these products stretches from the plausible to the wilder shores of paranoia. You can buy a portable subway strap so your hands never have to come into contact with the overhead bar, as well as a strip of vinyl that covers supermarket-cart handles. You can store your toothbrush in a $50 holder that kills germs with ultraviolet light.
But some scientists see value in bacteria. Throughout the late-twentieth century, there was a baffling rise in asthma and other allergies, and a group of researchers says the likely culprit is the scrupulous cleanliness of the developed world. In the late 1980s, a German doctor, Erika von Mutius, compared the incidence of allergies and asthma in children from East Berlin and West Berlin. She expected to find that children living in unhygienic, polluted, and economically disadvantaged East Berlin had higher rates than the children from the same genetic background who lived in clean, prosperous West Berlin. She found just the opposite.
The research of Mutius and others interested in the “hygiene hypothesis” has begun to fill in a picture of those who were most and least at risk. Children who had lots of siblings, who lived on farms, had cats, or went to daycare in their first year were discovered to do best at avoiding allergic diseases. Even children whose mothers had lived on farms during their pregnancies were less likely to become allergic. The children most likely to develop allergies and asthma were children who lived in cities, did not go to daycare, had no pets, washed their hands more than five times a day, and bathed more than once a day.
Today the hygiene hypothesis remains a hypothesis, but an increasingly respected one. There is both contrary evidence (the presence of dust mites and cockroaches has been associated with the development of asthma) and growing corroboration of the theory. So far there are no proven practical applications, although experiments are being conducted in several countries. In Perth, Australia, some asthmatic children are taking a “dirt pill” with the probiotic bacteria they apparently missed out on as babies and toddlers, and antioxidants. Other children with asthma will receive a placebo, and all will be monitored for frequency of attacks, tolerance for exercise, and breathing capacity. Japanese children who were given mycobacteria, a weakened form of tuberculosis bacteria that is related to soil bacteria, were found to have a significantly lower incidence of asthma and allergies than other children.
So far, no one has suggested feeding children actual dirt or relaxing hygienic standards to any great extent. Eventually, asthmatic and allergic children may take some kind of bacterial medication, but for the rest of us, Tore Midtvedt, a microbiologist at the Karolinska Institute in Sweden, advises a more moderate approach. He wants to see an end to “war on germs” thinking and a new understanding that reflects our often fruitful coexistence with germs. Midtvedt isn’t advocating that we live close to rats or fleas or drink polluted water, just that we stop trying to live in sanitized houses and bodies. “I’m not saying that we should be more dirty,” he says. “I’m saying we should be less clean.”