Risk Level: Medium-high.
“The surfaces of your eyes are a sensitive, exposed wet tissue, making them vulnerable to infection,” says Andrew Iwach, a San Francisco ophthalmologist and a spokesperson for the American Academy of Ophthalmology.

Watch Out For…

Eye Makeup and Tools (Curlers, Tweezers, Brushes): Makeup, including mascara and liner, can be a breeding ground for germs. “If contaminated makeup touches your eye, it could transmit an infection like pinkeye or staph,” says Howard Markel, a professor of pediatrics and communicable diseases at the University of Michigan Medical School, in Ann Arbor. Try using a disposable applicator at a makeup counter or test products on your hands, and avoid sharing makeup and tools.

Eye Medication: Using an eye medication that was prescribed for someone else, or that was prescribed to you for a previous infection, could reinfect your eye or cause a new infection.

Pillowcases: At home and in hotels, where linens tend to be laundered frequently, the risk is low. But try to avoid using pillows on airplanes (even if they’re wrapped in plastic) — they’re not cleaned as often.