A Little Dirt Won't Hurt

We live, the late paleontologist Steven Jay Gould said, in the "Age of Bacteria." If that's the case, we humans may want to make nice and stop treating our relationship with those numerous bugs like an epic battle. "Everything that's alive in this world today got here by learning to thrive in [spite of] infection," says Gerald Callahan, an immunologist at Colorado State University and author of Infection: The Uninvited Universe. Bacteria that routinely inhabit our bodies actually produce vitamins and proteins we need and help make our immune and gastrointestinal systems work.

Being excessively intolerant of bacteria can harm you, says Stuart Levy, microbiologist at Tufts University School of Medicine. Overuse of antibiotics can cause resistant bacteria; potentially, so can antibacterial hand soaps or cleaning products, which in the lab facilitate the growth of bacteria that trump commonly used antibiotics. Levy prefers regular old soap and water. If you must, he says, "use an antibacterial that doesn't leave a residue," such as an alcohol-, peroxide-, or bleach-based product.

"Let your kid play in the dirt," Levy adds. An overly hygienic infancy or childhood can raise a child's risk of asthma, type 2 diabetes, dermatitis, and Crohn's disease, studies suggest. Researchers have even found a soil microbe that appears to be helpful when it's injected into certain kinds of patients.