You've seen the commercials with the message: Moms (and Dads) don't get a day off. That company wants you to buy its product and get to work! And it's the same message from a guy in a suit downing an elixir to hide his symptoms so he can make a presentation to co-workers. Not smart!

If you're that sick, you're probably infectious; you'll pass the germs along with every breath and on every surface you touch. With the common cold, you're most contagious the first two to three days. The flu is contagious a day before symptoms appear (eek!) and up to a week after.

Going out into the world when you're sick costs your employer money (more sick employees, higher health care costs) and harms you and others. And even when you're feeling a bit better, until symptoms are gone, wash your hands frequently, sneeze into the crook of your arm, flush away used tissues, don't share food or drink.

A new study published in the journal PLoS Biology says that when you're sick you feel like staying in bed for a reason. Seems sickness behavior (crawling under the covers, refusing to talk to anyone) is a highly developed evolutionary trait that exists not only so you heal quickly and completely, but to help your group (that's family, colleagues, neighbors, etc.) as well. So, don't force yourself out of bed with symptom-quashing meds or iron willpower. Sleep, have some chicken soup, sleep some more. It's good for everyone.