(CNN) -- You're settled into seat 20D when you hear a sniffle, sniffle coming from seat 20B and a rumbling cough erupts from the occupant of 21A.

These aren't the cabinmates you were hoping for? Close contact with illness may be unavoidable if you're flying during cold and flu season.

Dr. David Weber, a professor at the University of North Carolina's schools of medicine and public health in Chapel Hill, urges travelers who are feverish and have upper-respiratory-tract infections to stay home.

"Unfortunately, people are often traveling for work or vacations, and if they spent a lot of money, feel they have to go," Weber said.

If you are one of those people, or are seated near one of those people on the plane, there are a few simple things you can do to boost your chances of staying healthy in the air and back on the ground.

Wash your hands

Since colds and the flu spread through droplets and close contact, it's important to wash your hands frequently with soap and warm water, particularly after touching surfaces others have recently touched or after shaking hands.

Weber recommends washing for 10 to 15 seconds with soap under running water. FDA-approved antiseptic liquid or foam hand cleansers also are effective, he said.

Avoid touching your eyes, nose or mouth, because germs are easily spread that way.

Cover mouth and nose

If you're coughing or sneezing, Weber suggested wearing a mask that covers your nose and mouth.

"If you don't have that, at minimum it would be nice to use a tissue to cover your nose and mouth when you sneeze," he said.

Containing the infection at the source is easier than trying to avoid contact with germs that are already in the cabin. However, uninfected passengers might also consider wearing a mask if they're seated near someone who is sick.
Drink plenty of fluids

Whether you're sick or not, drinking plenty of fluids is key to feeling good in flight, said Bonnie Taub-Dix, a registered dietitian and a spokeswoman for the American Dietetic Association. Low levels of humidity in airline cabins can have a dehydrating effect, particularly on long flights.

"It's really, really important to drink a lot of water or club soda," Taub-Dix said. She also advised passengers not to drink too much alcohol, which can cause dehydration.

Staying hydrated wards off headaches and the dry noses and throats that may leave passengers susceptible to infection.

Some frequent fliers swear by nasal sprays. Although there's no harm in them, Weber said he doesn't know of any data that show they help.

"You just want to drink lots of fluids, and then the body will keep your membranes moist."

Fortify yourself

A healthy diet rich in fruits and vegetables helps boost immunity all year long.

"Having foods that are rich in vitamin C, particularly fruits and vegetables, citrus fruits, vegetables like broccoli, would be a good idea," Taub-Dix said.

"A multivitamin and a vitamin C [supplement] might not be a bad idea for the winter season, in particular," she said.

Consuming vitamin C or zinc lozenges before a flight might help fend off illness, Weber said.

"I think they have some benefit, but they're not going to change your risk from 80 percent to 10 percent."

Flu shots are one of the best defenses, Weber said.

"Depending on where you're going and what the season is, obviously being properly immunized is important."