Flying can increase your risk of exposure to infection, but airlines are taking some precautions.

Air travel means spending time in security lines and airport terminals, which puts you into close contact with other people. As travel slowly recovers, planes are becoming more crowded, which means you will likely sit close to other people, often for hours, which raises your risk.

Once on a plane, most viruses and other germs don’t spread easily because of the way air circulates, according to the U.S. Centers for Disease Control and Prevention. Airlines also are focusing on sanitizing hard surfaces that passengers commonly touch.

Some airlines like Alaska, Delta, JetBlue and Southwest are blocking middle seats or limiting capacity. American, United and Spirit are now booking flights to full capacity.

All leading U.S. airlines require passengers to wear masks.

Several airlines announced Monday that they will ask passengers about possible COVID-19 symptoms and whether they have been in contact with someone who tested positive for the virus in the previous two weeks.