He could not see himself greeting "presidents, prime ministers, dictators, kings, queens" in the Oval Office while wearing one, he said.
"You do not have to do it," he said. "I don't think I'm going to be doing it."
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The guidelines issued by the Centers for Disease Control and Prevention, the government's public health advisory agency, came as the US reported more than 1,100 deaths in a single day - the highest total for a 24-hour period anywhere in the world.
The US has so far confirmed 278,458 cases of Covid-19 and more than 7,000 deaths, according to Johns Hopkins University.
Until now, US health authorities had said that only the sick, or those caring for patients of coronavirus, should wear masks, but newer studies suggest that covering up one's face is important to prevent inadvertent transmission.
However, he told reporters after announcing the CDC's new guidance: "I just don't want to do it myself."
Americans are now advised to use clean cloth or fabric to cover their faces whilst in public. Officials have stressed that medical masks remain in short supply, and should be left for healthcare workers.
The guidance comes as the number of cases globally climbs past one million. BBC
