"What we have said to people is there is clear scientific evidence now, by all the droplet experiments that happened, and that others have done, to show that a mask does prevent droplets from reaching others," Birx said on "Fox News Sunday" when asked what she would tell people who say they have a right not to wear a mask in public.
"Out of respect for each other, as Americans that care for each other, we need to be wearing masks in public when we cannot social distance," she said.
Birx was then asked by Fox's Chris Wallace whether she wished Trump wore a mask in public,
both from a messaging perspective and for safety reasons.
"Well the President did wear a mask while he was less than six feet in an occasion where that was important -- I think when he was traveling last week," Birx said. "I'm not with him every day and every moment, so I don't know if he can maintain social distance."
"I've asked everybody independently to really make sure that you're wearing a mask if you can't maintain the six feet. I'm assuming that in a majority of cases, he's able to maintain that six feet distance."
The comments from Birx come several days after Trump refused to wear a mask in front of cameras
while visiting a Ford plant in Michigan in what was another example of the President shrugging off the rules in place for others that are meant to guard against the coronavirus.
As he walked through the facility -- where Ford rules say everyone must wear a mask -- he was surrounded by company executives whose faces were covered.
Commenting on large crowds seen at beaches on Saturday
that appeared not to be social distancing, Birx stressed in an interview with ABC that "there's asymptomatic spread. And that means that people are spreading the virus unknowingly."
"And this is unusual in the case of respiratory diseases in many cases. So, you don't know who's infected. And so we really want to be clear all the time that social distancing is absolutely critical. And if you can't social distance and you're outside, you must wear a mask. These are items that really critical to protect individuals," she said.
Birx also left open the possibility of recommending the nation shut down again if there is another major outbreak, saying "it's difficult to tell" if she could see the country shuttering again.
She added there are preparations underway by the government if there is another wave,
saying "we are preparing for that potential fall issue, both in (personal protective equipment) ... and vaccine developments so we can be ready if the virus does come back in a significant way," she said on ABC.
Trump has previously opposed closing the country again amid a potential second wave of the virus.