One of the more difficult challenges in public health has been to teach people to wash their hands frequently and to stop touching the facial mucous membranes — the eyes, nose and mouth, all entry portals for the new coronavirus and many other germs.

“Scratching the nose, rubbing your eyes, leaning on your chin and your fingers go next to your mouth — there’s multiple ways we do it,” said Dr. Nancy C. Elder, a professor of family medicine at Oregon Health and Science University in Portland who has studied face touching among doctors and clinic staff members. “Everybody touches their face, and it’s a difficult habit to break.”

As communities prepare for the spread of coronavirus around the globe, the primary advice from health officials is for people to wash their hands. But a number of health researchers say the public health message also should include a more forceful warning about face touching.