Video: Matt Damon Debuts New 'Do

A nearly bald Matt Damon chatted with ET's Samantha Harris on Sunday, revealing how his new movie Contagion has changed his sanitation practices and explaining his new haircut.

"We live in New York City," said Matt. "So we wash our hands every time we get home and I'm much better about that now, having done Contagion."

Directed by Steven Soderbergh, Contagion casts Matt and Gwyneth Paltrow as an everyday couple and parents whose lives are forever changed when Gwyneth contracts a lethal airborne virus. As the fast-moving pandemic grows, the worldwide medical community races to find a cure and control the panic that spreads faster than the virus itself.

Gwyneth's character has a seizure early on in the movie, and Matt explained how the Oscar winner was able to pull off such a realistic performance in that pivotal scene.

"That was really all down to her being very specific with the medical examiners about what every part of her face would be doing - it's a close-up of her face," Matt explained. "It is just a very harrowing image."

As far as Matt's new image, he shaved his head for the movie he is currently filming called Elysium. Matt described the film, directed by Neil Blomkamp (District 9), as a Sci-fi flick, but it isn't scheduled to be released until March 2013.

Check out Contagion when it seeps into theaters September 9.