Some scientists believe the consequences of our germophobia are very real. As human health and hygiene have improved, the number of people living with asthma, allergies and inflammatory bowel disease has also been rising. For instance, the number of children with asthma doubled from 3.6 percent in 1980 to 7.5 percent in 1995, according to the Centers for Disease Control and Prevention; by 2005, 12.7 percent of children had been diagnosed with asthma at some point in their lives.
These diseases are often the result of a symphony of genes and environmental factors. But many scientists say the higher numbers can be explained, at least partially, by the hygiene hypothesis. Immune systems that are less accustomed to dealing with microbes may have hyperactive reactions, leading to the wheezing of asthma or the abdominal cramping of inflammatory bowel disease.
"As we're taking better care of our food, have less dirt and bacteria in our diet, and our immune system isn't being stimulated by those microbes," said Dr. Allen Meadows, an allergist and spokesman for the American College of Allergy, Asthma and Immunology.
Although an increase in hyperactive immunity may be an unfortunate side effect of living more sanitary lives, experts say we shouldn't throw the baby out with the bacterial bathwater. In general, it is a good thing that human life is generally more sanitary and some people have been able to lessen their exposure to malevolent microbes.
"Smallpox is not good for anyone," Schaffner said.
Blumberg noted that the study's findings don't mean that people should change anything about the way they try to keep germs at bay. Much more research is needed on just how germs benefit the human immune system.
"It's that middle road that we're seeking. Hand washing and reasonable cleanliness are a good thing," Schaffner said. "And let's all remember, many of the bad guys can be prevented through vaccination."