Hygiene Hypothesis: Why It May Be OK to Get a Little Dirty

Reader Contribution by Linda B. White and M.D
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I’ve heard that one of the theories scientists have put forth to explain the increase in asthma and allergy rates is called the “hygiene hypothesis.” What is the hygiene hypothesis, and how does it work?

Our immune systems were designed to cope with a germy world. Unless you live on a farm, postindustrial life can be relatively sterile. Theoretically, exposure to microbes and parasitic worms early in life matures the immune system, priming it to fight microbes rather than such innocuous things as pollen and dander. According to the hygiene hypothesis, a lack of exposure tips the immune system toward inflammation and allergic tendencies, as does the use of antibiotics in the first year of life. In addition, children born by caesarean section face a higher risk of allergies and asthma, because passage through the birth canal inoculates infants with bacteria that normally populate skin, the upper respiratory tract, guts and other organs. The development of healthy gut bacteria positively shapes the immune system.

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