It’s that time of year again, when travel—or any indoor activity, really—comes with concerns of catching the flu. The combination of the annual surge of influenza activity with still-lingering COVID strains is enough to make even savvy travelers worried about stepping into a crowded airport or boarding a plane.One of the paramount issues is determining if the air on planes hastens the spread of infection. But apprehensions about aircraft cabin air long predate COVID or active flu seasons. Before the pandemic, the Association of Flight Attendants—CWA was vocal about cabin air, as highlighted on its online Air Quality page, which details multiple concerns about shortages of oxygen and outside air, contaminated air supplies, and high concentrations of pesticides. In recent years these worries even spurred Congress to include further studies of contaminated air in the Federal Aviation Administration Reauthorization Act of 2018.