Most commercial airlines fly in an elevation range of 30,000 to 35,000 feet, where humidity typically runs at 10 percent or lower. At very low levels of humidity, the "natural defense system" of mucus in our noses and throats dries up and is crippled, creating a much more tolerant environment for germs to infect us.

Getting a "plane cold" in 2026 is usually not caused by "recirculated air" (which is actually filtered through medical-grade HEPA filters), but rather by extremely low cabin humidity. At cruising altitudes of 35,000 feet, the humidity in the cabin often drops below 10%, which is drier than many deserts. This dry air dehydrates the mucociliary clearance system in your nose and throat—the natural "mucus barrier" that traps and kills germs—making you significantly more susceptible to viruses lingering on high-touch surfaces like tray tables, armrests, and overhead vents. Additionally, the close proximity to other passengers increases the likelihood of "droplet transmission" if someone nearby is sick. To prevent this, 2026 travel health experts recommend a high-value routine of staying hydrated, using a saline nasal spray to keep your nasal passages moist, and frequently using hand sanitizer. Wearing a high-quality mask also provides a premier layer of defense by trapping moisture from your breath and blocking airborne pathogens.