We've all heard the old adage that the most important thing you can do to protect against colds and the flu is to regularly wash your hands – and it's true. To improve your chances of not contracting a cold, switch to a liquid soap, as germs can thrive on bars of soap. Hand sanitizers are also potent weapons against germs, but not all are created equal. Look for one with at least 60 percent alcohol, like Purell, which will kill the flu virus, advises Charles Gerba, an environmental microbiologist at the University of Arizona and coauthor of 'The Germ Freak's Guide to Outwitting Colds and Flu.' Hand sanitizers are also good for cold germs, but be sure to rub your hands until they're dry. If you can get to a sink, washing your hands is even more effective, says Philip Tierno , director of Clinical Microbiology & Immunology at NYU Langone Medical Center. He says to wash up as soon as you enter your home or office – and a quick rinse won't cut it. Scrub your hands (including beneath the nails) under water of any temperature for a full 30 seconds. Soap doesn't kill germs, but it gets them off your hands. Lastly, don't bother with antibacterial soaps: They're nothing more than slick marketing and are no more effective than regular soap.