Put away the bleach, get out the shovel! I now have even more support for dragging my 4-year old outside to play with mudpies while I weed. According to a recent article in the New York Times, we can now forget washing our kids' hands after they've been playing in dirt! There's this "Hygeine Hypothesis" that basically supposes that when a baby stick things in his/her mouths, it's a test drive of the immune system. The more exposure to bacteria, viruses, and worms, the baby has, the healthier that child will be as an adult!
I had heard/read before that people who grew up on farms or who had lots of pets, actually had fewer illnesses, so I felt justified in having two dogs (I was doing it for health!). And all teachers know that the first few years of teaching are pretty much spent with a cold, then after this immunity building period, it's rare to get sick again. This has also been somewhat supported by evidence that children that went to daycare are less sick in elementary school than children that stayed at home.
So get lots of pets, don't clean your house, let your kids roll around in the dirt, and don't feel guilty for sending your child to daycare!