Our shared spaces are crawling with invisible cohabitants: the germs that make us sick. We pass them to each other in direct encounters (a handshake, an uncontained sneeze within our personal space), but these harmful bugs can also lurk in our midst when no one is around — left on a common surface or object by someone we may never come into contact with, just waiting to be picked up.

“Any indoor environment where there is a group of people interacting provides a good opportunity for viruses to spread,” says Romney Humphries, a clinical microbiologist and assistant professor in UCLA’s Department of Pathology and Laboratory Medicine. That includes the typical office setting, as well as schools and daycare centers. “Kids tend to be like little virus factories,” Humphries says. “They shed much more virus than adults, and they bring it home to their parents, who take it into the workplace.”

To avoid succumbing to the same fate as the sneezy, fevery folks around us, it helps to know how the germs that cause colds, flu and other illnesses are transmitted. Humphries notes that the spread of germs can be largely explained by three F’s: fingers, feces and fomites. Fingers: For example, you shake the hand of a person who has just sneezed or coughed into it, or used it to wipe his nose. Then, at some point, you rub your eye or put that contaminated finger in your mouth, giving the germs an entry point. Feces: Sorry to be the bearer of this news, but microscopic fecal organisms can be picked up from surfaces (at daycare facilities, for example), swimming pools, and … well, there’s a reason for those signs in bathrooms imploring food service workers to wash their hands. “No one wants to hear it, but fecal-oral is one big way that viruses and bacteria are spread,” Humphries says. And fomites? Those are the objects and surfaces where the pathogen-containing droplets shed by others can settle. “Some bacteria and viruses survive quite well in the environment, others not so much,” Humphries explains. Influenza, she notes, can survive on hard surfaces for at least a day.

There is no fail-safe way to dodge whatever bug is being passed around, but you can reduce the odds. Humphries recommends doing the following to increase your chances of staying healthy when those around you are getting sick:

Wash Up

The most common way to pass harmful germs is by touching contaminated hands, objects and surfaces. Thorough and frequent hand-washing is the best defense, Humphries notes. Wet your hands, lather them with antibacterial soap, scrub, rinse and dry, and do this several times during the day — definitely after using the bathroom and before eating, but also in between, particularly when you’re in shared spaces. Keep an alcohol-based hand sanitizer by your desk to use when it’s not convenient to get to a faucet. Keyboards tend to be germ-ridden, so eating lunch at your desk, where you’re apt to web-surf or respond to emails in between bites, invites trouble.

Face Facts

As a second line of defense — given the likelihood that at certain times of the day some infectious bugs will live on your fingers — keep your hands away from your eyes, nose and mouth. If you need to wipe your nose or rub your eyes, use a tissue or do it with freshly scrubbed hands. “People touch their faces so many times during the day without even realizing it,” Humphries says. Awareness may help in overcoming the subconscious habit.

Wipe Out

Humphries recommends using bleach wipes a couple of times a day to dispose of the viruses and bacteria that populate your workspace (phone, desk, keyboard, mouse, etc.), waiting to wreak havoc.

Prepare for Battle

Beyond protecting your environment, taking commonsense measures to remain rested, relaxed and in good overall health can go a long way toward keeping up your immune defenses. In part, that means making regular and sufficient sleep a high priority and steering clear of too much stress. “If we’re well-rested and not too stressed out, we’re better able both to prevent ourselves from becoming infected and to fight off an infection that occurs,” Humphries says. She also recommends eating a well-balanced diet and points to the growing body of research suggesting that exercise boosts the immune system.

Take a Shot

There’s no vaccine to protect against the common cold, but we all can and should get an annual flu shot, Humphries says — both for ourselves and for those around us. The U.S. Centers for Disease Control and Prevention recommends that everyone 6 months and older take this preventive measure each year (ideally, early in the fall, before the start of the flu season), but many don’t. “People will say they never get the flu, or that they once got vaccinated and became sick anyway, when in reality it was either much less severe than it would have otherwise been or it was just a bad cold,” Humphries says. Tens of thousands of people die from influenza each year in the U.S., according to the CDC [Centers for Disease Control], with the elderly, young children and people with compromised immune systems among the most vulnerable. “Even if you think you’re healthy and don’t see the flu as a big deal, it’s a social responsibility to get vaccinated and protect those around you,” Humphries says.

When All Else Fails …

Speaking of social responsibility, in the event that you do come down with something, the best policy — for you and those around you — is to stay home and rest. You only have a mild case of the sniffles? Fine, go in and quarantine yourself in your office. To whatever extent you have to interact with others at work or at home, keep your distance and make sure to cover your mouth and nose when coughing or sneezing. But if you have a fever or are a mucusy mess, stay away. “We all hate to do that because we’re so busy,” Humphries says, “but by not going in you’re helping to protect the people in your environment from catching what you have, and you’re going to get better sooner.”