Parenthood 101 states that germs and bugs are bad and clean is good, right? A quick stroll down the cleaning product aisle confirms this with sprays, scrubs and powders offering to wipe out dirt and purify every surface with which our children come in contact. But new evidence suggests we might need to revisit this theory.

Actually, I take that back. The idea that germs protect against allergies first became news around 20 years ago. A researcher named David Strachan found that children with more siblings, particularly older brothers, were less likely to develop hay fever. Strachan's work didn't prove any definitive links, nor did it show exactly how the presence of older brothers kept younger siblings from developing hay fever. But it did ignite the theory that germs, whether they come from dirty hands to runny noses, might help kids in the long run. What's new is that researchers are beginning to link which bugs and which germs might protect against certain future illnesses.

Last fall, researchers analyzed data from the Philippines which tracked 20 years of information about kids starting when they were in utero. The data included information on the households the kids were born into as well as the sicknesses and symptoms their mothers reported them having before age 2. What they found was that kids who were exposed to more animal feces, and who had more diarrhea before they turned 2, tended in their early 20s to have lower levels of C-reactive protein, a key marker of inflammation. This lower level of C-reactive protein may be associated with a lower risk of inflammation-based illnesses like rheumatoid arthritis or heart disease.  

In another study, preschoolers who tested positive for Helicobacter pylori, a bacterium that lives in the stomach lining of as many as half the world's people, were less likely to suffer from the itchy skin disorder atopic eczema, a hypersensitivity reaction similar to an allergy. In another study, the presence of H. pylori was linked to a lower risk of childhood asthma.

Exposure to hepatitis A, a virus transmitted via contaminated food and water, may also be able to boost a child's immune system. According to researchers at University College of London, kids with a certain common gene variant who had been exposed to hepatitis A appeared to be less likely to suffer from a range of allergic disorders.  

But not all germs and viruses lead to future immune protection. In a study done at the Arizona Respiratory Center, researchers found that children hospitalized for severe respiratory syncytial virus, bronchiolitis, or the flu may be more likely to develop asthma later on.  

When it comes down to it, there is no set instructions for which bugs and germs might protect kids from future illnesses. Due to the potential for deliberate infection, it's not a good idea to purposely expose kids to potential pathogens. But as a parent, this new information does tell me that in most cases, exposing kids to the natural world — whether they're playing with worms in the garden or snuggling up to the dog on the sofa — will benefit them in more ways than we can imagine.

[via Slate]

Dirt and your child's health
New study maps how bugs and virus help children develop immunity.