The Associated Press – Public health experts say staying home is best to keep yourself and others safe from infection. But if you are thinking about flying for the holidays, you should know what to expect.

Flights are getting more crowded and more airlines plan to stop blocking seats to accommodate the growing number of people taking to the skies again.

Starting December 1, Southwest will join United and American in allowing every seat on planes to be sold. JetBlue will scale back the number of blocked seats, and—along with Delta and Alaska—plans to drop all limits sometime next year.

The airline industry says it is safe to fly, pointing to a report it funded that found the risk of viral spread on planes very low if everyone wears a mask, since planes have good ventilation and strong air filters.

But the U.S. Centers for Disease Control and Prevention notes that sitting within 6 feet of others—sometimes for hours—can still increase your risk of getting infected. And though airlines are still requiring passengers to wear masks, there is no guarantee everyone will comply. More than 1,000 people who refused to wear masks have been banned by U.S. airlines.

Remember that flying also means spending time in airport security lines and gate areas, where you might come into close contact with others.

In an October update on travel, the CDC recommended checking whether infections are rising in the area you are traveling to.