A soul patch or a Zorro mustache is OK, but steer clear of the Fu Manchu, muttonchops or a full beard.
A playful Centers for Disease Control and Prevention graphic warns that some facial hair styles could prevent face masks and respirators from working as well as they should.
"Facial hair that lies along the sealing area of a respirator, such as beards, sideburns, or some mustaches, will interfere with respirators that rely on a tight facepiece seal to achieve maximum protection," guidance from the federal health agency says.
The graphic published during No-Shave November in 2017 got renewed attention this week as people worldwide try to guard against the coronavirus.
Like a game of Guess Who? with just one guy, the graphic shows a man with 36 styles of facial hair, and check marks or x's indicating whether each style is compatible with a respirator.
The CDC does not recommend the use of face masks to try to avoid contracting the coronavirus. Instead, Americans are advised to wash their hands frequently, avoid contact with people who are sick and disinfect frequently touched surfaces.
Buying face masks you don't need could hurt medical professionals who really need them, experts told CNBC.
"Panic purchases of face masks in low-risk countries like the U.S. is not warranted," professor of emerging infectious diseases Annelies Wilder-Smith said.
The CDC does recommend the use of face masks for people with coronavirus symptoms and those who take care of them.