Shock studies periodically expose and deplore sloppy habits. Fully 76% of kitchen sink cloths are infested with germs. One in three American men does not wash his hands after using a public lavatory.
There is nothing fixed, however, about Western fascination with dirt—or terror of it. As recently as 1965 only half of British women wore an underarm deodorant. Back in 1940 just over half of American households had a proper bathroom. In 1951 nearly two-fifths of English households lacked a bath—and not only for reasons of post-war poverty.
Regular all-over bathing, elaborated in ancient Greece and Rome and celebrated in luxurious contemporary ensuite bathrooms, was distrusted for about 400 years in the second millennium. Water was thought to carry disease into the skin; pores nicely clogged with dirt were a means to block it out. In the 17th century the European aristocracy, who washed little, wore linen shirts in order to draw out dirt from the skin instead, and heavy perfumes and oils to mask bad smells.
Has the persecution of dirt, however, gone too far? Some immunologists believe that children now growing up in hyperclean, sterile environments are failing to develop immune systems properly because of inadequate exposure to bacteria. This idea, known as the hygiene hypothesis, is a possible explanation for growing incidences of eczema and other allergic diseases in rich countries, which are rare in poorer ones. Various studies have shown that children growing up with older siblings, who bring germs into the house, or on farms, where they come into daily contact with animals, muck and unpasteurised milk, are less likely to develop hay fever or asthma, though the scientific evidence is not conclusive.
A recent experiment by dermatologists at the University of California, San Diego, suggests a molecular basis for the hygiene hypothesis. They found common bacteria living on the surface of skin that can help wounds to heal by releasing a special molecule to stop outer-skin cells getting inflamed. Bacteria-free skin, in other words, may provoke inflammation and slow healing.
First-time parents, writes Mary Ruebush, an American immunologist and author of “Why Dirt is Good”, frantically try to keep their babies away from dirt. “When that pacifier falls on the floor, the parents cannot throw themselves on it quickly enough to wash it off, soak it in bleach, run it through the dishwasher, the microwave, you name it.” The trouble is, she adds, such a baby will not have the contact with germs that are needed to build up a strong immune system. Children rather should be encouraged to play in the dirt.
Some researchers in Britain have even found what they think might be dirt that can make people happy. An experiment on mice showed that certain bacteria normally found in soil stimulated neurons in the brain that produce serotonin, which influences mood. The results, says Chris Lowry, at Bristol University, “leave us wondering if we shouldn’t all be spending more time playing in the dirt.” From demon and pest to guarantor of happiness and childhood health? Not bad for humble grime.
