What Happens When an Astronaut Sneezes?

Best to do the sneezing inside a shuttle or the space station, not on a spacewalk, when it can get real messy, with goo sprayed all over the inside of the helmet's "windshield."

Lately astronauts have been complaining about stuffy heads up there on the International Space Station. NASA doesn't think they have colds, though. Rather, the effects have more to do with pockets of carbon dioxide generated when they gather in groups, space station flight controller Heather Rarick said.

Astronauts have been sick in space before, even though NASA puts them through a rigorous quarantine before each launch in an effort to prevent colds and flus from being launched.

Thing is, microgravity is thought to weaken the immune system. Oh, and as we all know, you don't have to have a cold to generate a good, gooey sneeze.

On Earth, health experts recommend you sneeze into your elbow to keep viruses to yourself. On a spacewalk, that's not an option. Here's what you want to do:

"Aim low, off the windshield, because it can mess up your view and there's no way to clear it," said six-time spacewalker Dave Wolf. "That's how you do it."

• The Gross Science of Coughs and Sneezes