Even if you think you're staying germ-free with hand sanitizers and individually-wrapped cough drops, beware of these danger zones.

KEYBOARDS: The average desk harbors 400 times more bacteria than the average toilet seat, says Charles Gerba, Ph.D., a microbiologist at the University of Arizona in Tucson. Don't swap workstations with anyone and always do a wipe-down before you clock out.

CELL PHONES: Because germs multiply in warm places, the heat the phone generates makes it a breeding ground, Dr. Gerba says. (A recent U.K. study found cell phones are grosser than public restrooms.) Unless you have the new Motorola with antimicrobial coating, keep your cell phone to yourself and douse it with antibacterial cleaner daily.

PENS: Carry your own. When signing the credit card slip at the checkout, whip out your own instrument rather than using the one the clerk offers, Dr. Schachter says. There are more than fingerprints on that puppy.

PUBLIC RESTROOMS: Use a paper towel to turn faucets. And use the end stalls; most people use the middle stalls, so those tend to be, uh, buggiest.

KIDS: Along with mud, kids also trek in loads of germs. Especially during cold-and-flu season, make it a rule that they must wash their hands the minute they walk through the door, says William Schaffner, M.D., professor and chair of preventive medicine at Vanderbilt University School of Medicine in Nashville.

ATMs: There's no telling whose hands have been touching that keypad after a fit of sneezes. Dr. Schachter recommends stashing a travel-size bottle of an alcohol-based hand gel like Purell in your purse.