Dear Doctor: I work in an open-plan office, and people aren’t good about staying home when they’re sick. Would wearing a surgical mask help keep me from catching someone’s cold or flu?

Dear Reader: It’s the height of our annual cold and flu season, so we understand your concern. Although the viruses responsible for respiratory illnesses are present year-round, they cause the largest numbers of illnesses in the winter months, when cold weather and short days keep people indoors. We spend a lot of time in close quarters, and in spaces that are often poorly ventilated. All of this makes it easier to transmit – and to become infected by – the viruses that cause influenza and the common cold.

Before discussing the pros and cons of a surgical mask, it’s useful to understand how viruses spread. A virus is a parasite that’s so tiny, it can only be viewed through an electron microscope. The influenza virus, for example, is 1,000 times smaller than a single grain of salt. It enters the body via the mucous membranes in the mouth, nose and eyes. Once inside a host, the virus injects its genetic material into a susceptible cell, hijacks that cell’s machinery and forces it to churn out millions of copies of the virus. The immune system promptly attacks the invaders, which causes the array of symptoms that make the flu such a misery – fever, aches and pains, headache, exhaustion, coughing, sneezing and copious mucous production.

With every cough and sneeze, a sick person sends out a virus-packed aerosol mist that can travel 6 or 8 feet, bits of which can linger in the air for several hours. When a healthy person inhales the expelled droplets or picks them up from a contaminated surface and then touches their mouth, nose or eyes, they can become infected with the virus.

Unfortunately, when it comes to using a mask to protect against viruses, the evidence is mixed. Some studies, which focused on health care workers in hospital situations, found that masks can be effective at preventing infection when worn properly and used consistently. But the weave is too loose to filter all viral materials, and masks don’t always stay snug. Those same face masks may actually be more effective when worn by someone who is sick, since they block the spray of infectious matter from a cough or a sneeze.

If it makes you feel better, go ahead and wear a mask. But be sure to also follow additional precautions. Wash your hands frequently with soap and warm water, or use a hand sanitizer. Avoid touching your face since, as we mentioned, the mucous membranes of the nose, mouth and eyes are entry points for the virus. If you’re wearing a mask and then rub your eyes, you’ve defeated the purpose.

If you haven’t already done so, be sure to get a flu shot. Flu season typically peaks in January and February and lasts until the spring, so there’s still time for the vaccine to be helpful. And if you do get sick, please seek medical care.

Send your questions to askthedoctors@mednet.ucla.edu.