The clean fad

France’s Henri IV was famously filthy, “stinking of sweat, stables, feet and garlic”. Upon learning that the Duc de Sully had taken a bath, the king turned to his own physician, André du Laurens, for advice. The king was told that the poor man would be vulnerable for days. So a message was dispatched informing Sully that he was not to go out, or he would endanger his health. Instead, he was told, the king would visit his Paris home: “so that you come to no harm as a result of your recent bath.”
I've always been a bit persnickety -- I hate getting myself gunked up with mud, say, or grease. But perhaps strangely, a bit of basic dirtiness has never bothered me tremendously. Maybe it comes of travel: even before I got to Azerbaijan and the pipes in my village froze up for the winter and every bus ride was ripe, missing a shower never left me a trembling heap of fear. It turns out, that's not necessarily such a bad thing:
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.