Too lateGreg Williams' WikiWorldEverybody knows the Five Second Rule, right? That it's OK to eat food that falls to the ground if it's picked up within five seconds? The Washington Post has a nice article today, "Hypercleanliness May Be Making Us Sick," delving into the Hygiene Hypothesis that suggests that exposure to various germs early in life protects against the later development of allergies, asthma, and various auto-immune diseases. The idea is that your immune system gets practice fending off real threats and doesn't later overreact to innocuous things like cat dander.  As the Post explains:

A growing body of evidence suggests that all the antibacterial-wiping, germ-killing cleanliness of the developed world may actually be making us more prone to getting sick — and that a little more dirt might help us stay healthier in the long run...

Here’s what researchers do know: Our immune systems need bugs. They rely on early encounters with germs to learn how to protect our bodies.

“Bacteria, fungi, lots of these things we think of as bad — they’re all part of our environment, and we evolved to live with them,” says Michael Zasloff, an immunologist and physician at MedStar Georgetown University Hospital. Through exposure to these microbes early in life, your immune system learns what’s harmful and what isn’t, he says, and that readies the immune responses you’ll have for the rest of your life.

“The body has got to know friend from foe,” Zasloff says. If your body learns that a specific microbe or substance — any antigen, or visitor to the body — is a foe, it will send immune system cells to destroy it. If it recognizes the antigen as a friend, the immune system will leave it alone. “Exposure tells the immune system, ‘These are the things you’re going to run into all the time, so you don’t need to worry about them.’ ”

Support for the Hygiene Hypothesis comes from research comparing farm and city kids. Farm kids are less likely to suffer from allergies and asthma than are city kids. Why? Because they are exposed to more microbes from livestock, muck around in barns, etc.

So what does this have to do with the Five Second Rule? The Post reports:

Zasloff goes even further. He doesn’t mind if his kids eat a little dirt, don’t wash their hands before every meal or wear the same socks twice. Eating food that’s been in the fridge a while or that has fallen on the floor is okay, too, he says.

That being said, Zasloff does caution: "Use your common sense."

Disclosure: I am something of cleanliness nut, but I do practice the Five Second Rule. Also, despite having grown up on a dairy farm, I am allergic to our two cats. Fortunately, the modern miracle of daily Zyrtec solves that problem.