The federal government scrambled Friday to stave off a potential wave of public health emergencies sparked by President Trump’s dangerous suggestion that injecting bleach or other household disinfectants into the body might cure people of the novel coronavirus.

It was only the latest dubious medical tip from a president struggling to contain a pandemic that has claimed the lives of more than 50,000 Americans. The Food and Drug Administration warned Friday against the use of hydroxychloroquine — the anti-malarial drug that Trump repeatedly has promoted as a “game-changer” miracle cure for covid-19 — because it has been found to cause serious heart rhythm problems.

At Thursday night’s White House coronavirus news conference, Trump used his pulpit to float the idea of injecting a disinfectant into one’s body “almost as a cleaning” — a prescription that surprised some aides who said it seemed to come out of nowhere.

Within hours came a universal rejection of the president’s hypothesis, as urgent bulletins were issued — including from inside Trump’s own administration — warning the public of potentially lethal dangers.

FDA Commissioner Stephen Hahn said on CNN, “I certainly wouldn’t recommend the internal ingestion of a disinfectant.” Three hours before Trump spoke, the Environmental Protection Agency had advised people never to “ingest disinfectant products.” Surgeon General Jerome Adams implored followers on Twitter to “PLEASE always talk to your health provider first before administering any treatment/medication to yourself or a loved one.” And the manufacturer of Lysol said that “under no circumstance” should its disinfectant be administered into the human body.

Trump’s latest fantasy cure mushroomed into a potential crisis for public health officials. In Maryland alone, the state government’s emergency hotline received more than 100 calls from residents inquiring whether injecting a disinfectant really was a cure.

At the White House, the explanations for Trump’s faulty suggestion varied widely. Newly minted press secretary Kayleigh McEnany accused the media of “irresponsibly” taking Trump’s comments out of context.

A few hours later, however, Trump made clear his comments were accurately reported, only he claimed he had said them in jest.

“I was asking a question sarcastically to reporters like you just to see what would happen,” Trump told reporters Friday in the Oval Office. The president did not offer a rationale for why it would be appropriate for a leader to joke about medical treatments while updating the nation about a pandemic.

Later in the day, Deborah Birx, a physician and the White House coronavirus response coordinator, defended the president’s comments about ingesting disinfectant — not as sarcasm, but as part of a deliberate, if unorthodox, thought process.

“When he gets new information he likes to talk that through out loud and really have that dialogue, and so that’s what dialogue he was having,” Birx said on Fox News Channel.

The extraordinary uproar over ingesting disinfectants underscored what public health experts say is the danger when the president — who has no training in medicine, a proud aversion to studying details and a supreme confidence in his own expertise — speculates about science during a pandemic.

Compounding the situation is the timidity and at times reluctance with which the physicians advising Trump intervene to correct the president or refute his theories, said Jack Chow, a former U.S. ambassador for global HIV/AIDS in the George W. Bush administration and a former World Health Organization assistant director general.

Anthony S. Fauci, the longtime director of the National Institute of Allergy and Infectious Diseases, did not attend Thursday’s briefing.

Birx was present, sitting silently and visibly straining to control her facial expressions as Trump talked up the possibility of disinfectant injections to cure covid-19. When Trump asked her whether heat and ultraviolet light could be another cure, Birx replied, “Not as a treatment,” although she noted that having a fever could help one’s body respond.

“Sometimes you just need to say the president’s wrong,” said a former administration official who, like some others interviewed for this story, spoke on the condition of anonymity to be candid. “I understand picking your spots, but sometimes you’re doing the president a favor by saving him from himself.”

Trump’s commentary seemed to be inspired by a presentation from a Department of Homeland Security official about a promising but still inconclusive government study exploring the possibility of heat, humidity and light to kill the virus, as well as the effectiveness of disinfectants in killing it on surfaces such as tables, countertops and office workspaces.

William Bryan, the department’s acting undersecretary for science and technology, first shared the study with members of the White House coronavirus task force on Wednesday and returned Thursday. He said his department had studied the virus in an air chamber and never said chemicals or UV light had been studied on humans nor suggested they be used in humans, according to several administration officials.

Fauci raised concerns about Bryan’s presentation, warning that if he gave too many suggestions on temperature and surfaces people might make bad decisions. As one senior administration official put it, “He didn’t want this to be seen as the cure for humans.” Fauci’s recommendations were accommodated, according to a White House official.

Others on the task force, including Birx, White House chief of staff Mark Meadows, as well as McEnany and others in the communications and press shops, were concerned that the Department of Homeland Security study had not been thoroughly vetted. “It was not ready at all to go to the president,” the senior official said. “There was no guideline. There was no data. There was nothing.”

Still, Vice President Pence and his team wanted Bryan to present the information to the president and to the public, eager to have something positive to share. They hoped the study would help encourage people to spend more time outdoors and to disinfect their homes, aides said.

On Thursday, shortly before his news conference, Trump — who does not regularly attend the task force meetings — received a private briefing by Bryan that lasted about 15 minutes, aides said.

The plan, they said, was for Bryan to present the study on camera and for Trump to talk about other matters. But once they stepped to the rostrum in the press briefing room, the president veered off script and weighed in on the study.

“I see the disinfectant, where it knocks [the virus] out in a minute — one minute — and is there a way we can do something like that, by injection inside, or almost a cleaning,” Trump said, referring to the human body. “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. So, that, you’re going to have to use medical doctors with. But it sounds interesting to me.”

Later, when he was asked whether it was dangerous to present unproven theories to the public, Trump snapped: “I’m just here to present talent. I’m here to present ideas, because we want ideas to get rid of this thing.”

White House officials and outside advisers were concerned that Trump’s comments could lead to people ingesting bleach or making other questionable decisions, but many were reluctant to contradict him publicly.

An exception was Scott Gottlieb, the former FDA commissioner who advises the task force. “There is absolutely no circumstance in which you should ingest a disinfectant or inject it for the treatment of any condition, including coronavirus,” Gottlieb said in a brief interview.

White House spokesman Judd Deere said in a statement Friday night, “The media has lost control with their mischaracterizations and outlandish headlines about what the President said, and completely ignore that he has consistently emphasized that Americans should consult with their doctors regarding coronavirus treatment.”

In an apparent concession that Thursday’s performance had been damaging and after conversations with a number of aides, Trump took no questions at Friday’s unusually short daily briefing, and briefings were not scheduled for the weekend, officials said. Advisers said there were discussions in the White House about slashing the frequency going forward.

Some in Trump’s orbit placed blame on Bryan, arguing that he was not up to the task of briefing the president and allowed for Trump to get confused or to conflate the study’s findings. Some White House officials, concerned about the briefing, arranged a last-minute session to quiz Bryan, three officials familiar with the matter said.

Regardless, it was the president who floated the idea of an injection of disinfectant — something that shocked a number of his aides. “No one knows where it came from,” said a senior administration official.

Steve Schmidt, a former top adviser in the George W. Bush White House and a vocal Trump critic, said, “As reckless as it is, it’s absurd that the president of the United States is on a stage telling the American people to shoot up Lysol to cure the virus.”

“These briefings have become a daily symposium on unfitness,” Schmidt said. “He gets up there, he’s completely unprepared, he has no idea what he’s talking about and he says things that shock the conscience and make no sense.”

At the Centers for Disease Control and Prevention, where government scientists have been studying the coronavirus, officials had no warning that Thursday’s news conference would feature Bryan’s presentation, nor that the president would opine about injecting disinfectants.

On Friday afternoon, the agency tweeted a warning that “household cleaners and disinfectants can cause problems when not used properly.” The CDC is considering what additional health information it may need to release to ensure that people are “not inadvertently harmed by doing something that appears to be endorsed by the president,” said a federal health official.

One concern is that people may think they can use a nebulizer — a piece of medical equipment that a person with asthma or another respiratory condition uses to administer medication directly and quickly to the lungs — to safely use Listerine mouthwash.

The CDC issued a report Monday that found U.S. poison control centers were seeing a surge in calls about exposure to cleaners and disinfectants amid the coronavirus outbreak. Between January and March, there were 45,550 calls — a 20.4 percent increase from the same period last year.

The report said that although the data did not include information indicating a “definite link” between exposures and cleaning efforts related to the coronavirus, “there appears to be a clear temporal association with increased use of these products.”

Household bleach ingestions are some of the most common incidents called in to U.S. poison control centers each year, said Jon Cole, medical director of the Minnesota Poison Control System. Most involve small children getting their hands on cleaning products, which are so diluted that injuries are typically minor and contained to the mouth and throat, he said.

Injecting bleach, however, would be far more dangerous, Cole said. The chemicals would probably cause anemia and kidney damage by breaking apart red blood cells and harming the kidney’s ability to filter toxins from the blood.

Patrice A. Harris, president of the American Medical Association, said Friday, “It is unfortunate that I have to comment on this, but people should under no circumstances ingest or inject bleach or disinfectant.”

Last month, after Trump declared that hydroxychloroquine was a “game-changer” in the fight against the virus, an Arizona couple noticed the pharmaceutical name matched the label on a bottle of chemicals they used to clean their koi pond. The couple ingested the chemical, chloroquine phosphate, hoping to stave off an infection. The husband died shortly after arriving at a Maricopa County hospital, according to the hospital. The wife survived.

That incident prompted the CDC to issue a health advisory alert March 28 to thousands of clinicians across the country warning them about dangers of chloroquine phosphate, “which can cause serious health consequences, including death.”

Lenny Bernstein, Rachel Weiner and Ovetta Wiggins contributed to this report.