Take two intestinal worms and call me in the morning

What do you do when your bacon-wrapped cookie falls to the ground? Why, pick it up and eat it, of course! If the floor is dirty, even better! Bonus germs!

An increasing number of studies are supporting the hygiene hypothesis, which proposes that early exposure to cooties encourages the development of a well-tuned immune system.

The hypothesis is commonly cited as a possible explanation for the rise of autoimmune diseases, such as allergies and asthma, in developed nations. Supposedly, a squeaky clean environment results in a bored immune system that starts tasering harmless things, like pollen, some food items, or in some cases, the very body it's supposed to protect.

Harmless bacteria and happy-go-lucky viruses are all good for the development of the immune system, but the "It" girl of hygiene hypothesis is turning out to be—get your cameras ready!—the intestinal worm. Most worms are harmless in healthy people, because human beings have adapted to their presence. 

Some worms seem to be good at preventing some bowel diseases (such as ulcerative colitis and Crohn’s disease). A few showed promising potential to even reverse autoimmune diseases! In one study, subjects stricken with multiple sclerosis who were subsequently infected with human whipworm (in the course of life, not by the researchers) had mellower versions of their disease. (The University of Wisconsin Madison is conducting a similar study. Imagine the recruitment poster for that study!) 

Everyone wants to hear about intestinal worms during dinner parties, so load up on materials by doing a Google search. For a great overview on the studies, check out the Evolution and Medicine Review and the New York Times (registration required).