Even the makers of Clorox and Lysol pleaded with Americans not to inject or ingest their products.

The frantic reaction was prompted by President Trump’s suggestion on Thursday at a White House briefing that an “injection inside” the human body with a disinfectant like bleach or isopropyl alcohol could help combat the virus.

“And then I see the disinfectant, where it knocks it out in a minute,” Mr. Trump said after a presentation from William N. Bryan, an acting under secretary for science at the Department of Homeland Security, detailed the virus’s possible susceptibility to bleach and alcohol.

“One minute,” the president said. “And is there a way we can do something like that, by injection inside or almost a cleaning? Because you see it gets in the lungs and it does a tremendous number on the lungs. So it would be interesting to check that.”

Mr. Trump’s remarks caused an immediate uproar, and the White House spent much of Friday trying to walk them back. “Leave it to the media to irresponsibly take President Trump out of context and run with negative headlines,” Kayleigh McEnany, the new White House press secretary, said in a statement criticizing the coverage of Thursday night’s briefing.

But the president later undermined her argument by insisting that his question to Mr. Bryan in fact had been an elaborate prank that he had engineered to trick reporters.