Doctors and health experts urged people not to inject disinfectant on Friday after U.S. President Donald Trump suggested scientists should investigate whether putting the cleaning agent into the body could be a way to combat COVID-19.

"[This is an] absolutely dangerous, crazy suggestion," said Paul Hunter, a professor of medicine at Britain's University of East Anglia.

"You may not die of COVID-19 after injecting disinfectant, but only because you may already be dead from the injection."

Trump said at his daily media briefing on Thursday that scientists should explore whether putting light or disinfectant into the bodies of people infected with the new coronavirus might help them clear the disease.

"Is there a way we can do something like that by injection, inside, or almost a cleaning?" he said. "It would be interesting to check that."

Trump looked over at Dr. Deborah Birx while making the comments. The co-ordinator of one of the White House's coronavirus task forces appeared uncomfortable and caught off guard.

Dr. Deborah Birx, White House coronavirus response co-ordinator, is shown during Thursday's media briefing. (Alex Brandon/The Associated Press)

The White House said on Friday that Trump had been taken out of context and had urged people to seek coronavirus treatment only after conferring with their doctors.

White House press secretary Kayleigh McEnany said in a statement: "President Trump has repeatedly said that Americans should consult with medical doctors regarding coronavirus treatment, a point that he emphasized again during yesterday's briefing."

ALERT🚨: We have received several calls regarding questions about disinfectant use and <a href="https://twitter.com/hashtag/COVID19?src=hash&ref_src=twsrc%5Etfw">#COVID19</a>.<br><br>This is a reminder that under no circumstances should any disinfectant product be administered into the body through injection, ingestion or any other route. —@MDMEMA

The emailed statement did not directly mention cleaners or ultraviolet (UV) light as coronavirus treatments, but its subject was "White House on disinfectant."

Trump himself offered a different explanation from the White House while signing the latest coronavirus relief bill, stating he was being sarcastic.

"I was asking a sarcastic — a very sarcastic question — to the reporters in the room about disinfectant on the inside. But it does kill it."

'Under no circumstance': Lysol

Reckitt Benckiser, which manufactures household disinfectants Dettol and Lysol, issued a statement on Friday.

"Under no circumstance should our disinfectant products be administered into the human body [through injection, ingestion or any other route]," the company said.

Trump's comments were also met with alarm by the medical experts that the U.S. news networks employ as contributors.

"I just don't think we should be normalizing that in any way, shape or form," said Dr. Sanjay Gupta on CNN.

In the same segment, Dr. Leana Wen said the experts serving in the administration are engaged in a difficult balancing act of needing to tell the truth "while at the same time not upsetting the president so much that they can't be credible in his eyes."

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The comments were also pounced on by former vice-president Joe Biden, the presumptive Democratic nominee for president in the November election.

"UV light? Injecting disinfectant?," said Biden. "Here's an idea, Mr. President: more tests. Now. And protective equipment for actual medical professionals."

Waiting on a sunny day

Trump's comments came after a U.S. official in the briefing suggested the coronavirus appears to weaken more quickly when exposed to sunlight, heat and humidity, in a potential sign that the pandemic could become less contagious in summer months.

U.S. government researchers have determined that the virus survives best indoors and in dry conditions, and loses potency when temperatures and humidity rise – and especially when it is exposed to sunlight, said William Bryan, acting head of the U.S. Department of Homeland Security's Science and Technology Directorate.

For people who want to know how the 'bleach injection' thing got started, here is the transcript of the relevant snippets in the White House press conference 1/2 <a href="https://t.co/39V3wkwYkn">pic.twitter.com/39V3wkwYkn</a> —@Alex_Panetta

"The virus dies quickest in the presence of direct sunlight," he told a White House news briefing. On non-porous surfaces like stainless steel, the new coronavirus takes 18 hours to lose half its strength in a dark, low-humidity environment, Bryan said.

In a high-humidity environment, that half-life dropped to six hours, and when the virus was exposed to high humidity and sunlight, the half-life dropped to two minutes, he said.

Researchers found a similar effect with the coronavirus that was suspended in the air, simulating the coughing or sneezing that often spreads the disease. In a dark room, the virus maintained half its strength for an hour. But when exposed to sunlight, it lost half its strength in 90 seconds, Bryan said.

Researchers also found that isopropyl alcohol was a more effective disinfectant than bleach, he said.

The findings could bolster hopes that the coronavirus will mimic the behaviour of other respiratory diseases like influenza, which typically are less contagious in warm weather.

William Bryan with the Department of Homeland Security, left, is seen with the U.S. president and Vice-President Mike Pence. On Thursday, Bryan briefed media on potentially positive news about how the novel coronavirus responds to humidity and sunlight. (Jonathan Ernst/Reuters)

But the coronavirus has also proven lethal in warm-weather places like Singapore, raising broader questions about the impact of environmental factors.

"Neither sitting in the sun nor heating will kill a virus replicating in an individual patient's internal organs," said Penny Ward, a professor in pharmaceutical medicine at Kings College London and chair of the education and standards committee of the faculty of pharmaceutical medicine.

'I'm here to present ideas'

Trump lashed out at a Washington Post reporter who wondered if it was "dangerous" for him to be making unproven statements to Americans regarding sunlight and the virus.

"I'm here to present ideas because we want ideas to get rid of this thing," the president said.

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Trump, in his bid to provide optimistic news as the country grapples with the deadly pandemic, has previously been criticized for touting drugs whose efficacy in treating patients with the coronavirus has not been proven and which sometimes lead to deadly side-effects.

The U.S. Food and Drug Administration on Friday cautioned against the use of malaria drugs, hydroxychloroquine and chloroquine, in COVID-19 patients because of the risk of serious heart rhythm problems.

The agency said it was aware of increased use of these medicines through outpatient prescriptions and the drugs could cause abnormal heart rhythms and dangerously rapid heart rates.

General concerns that political considerations may have overridden science reached Capitol Hill this week after a vaccine specialist revealed he was reassigned.

Rick Bright, former director of the Biomedical Advanced Research and Development Authority, or BARDA, said on Wednesday he was replaced as its director because he resisted the Trump administration's efforts to push hydroxychloroquine and the related chloroquine.

He has filed a whistleblower complaint, and Democrats are also asking questions about his reassignment.

Disagreement over testing

Trump has also made rosy statements about the extent of coronavirus testing and the development of a potential vaccine that have been questioned.

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Another example of that came Thursday when he was questioned about comments Dr. Anthony Fauci made to Time magazine.

Fauci, the head of the National Institute of Allergy and Infectious Diseases, said the U.S. capacity to test needs to be ramped up and is being hampered by a lack of swabs and reagents, among other factors.

"I am not overly confident right now at all, that we have what it takes to do that," said Fauci.

Hours after those comments came to light, Trump replied to a reporter: "I don't agree with him on that, no, I think we're doing a great job on testing."