Doctors, epidemiologists and others reacted with alarm after US President Donald Trump on Thursday suggested that injecting disinfectant and exposure to ultraviolet rays could help people with the coronavirus.

“Trump is absolutely wrong and irresponsible,” Dr Eugene Gu, whose laboratory is involved in coronavirus testing, wrote on Twitter, adding, “Clorox, Tide Pods and Lysol will kill coronavirus. No question about it. But if you are infected then the coronavirus is inside your cells. If you use any of those disinfectants to kill the coronavirus in your own cells then you’ll die right along with the coronavirus.”

Trump made the comments during his daily news briefing at the White House, after a discussion on work by government researchers on the effect of heat and sunlight on the coronavirus.

He first mused on whether light could be brought inside the body before moving onto the subject of disinfectant.

“I see the disinfectant where it knocks it out in a minute,” Trump said. “One minute! And is there a way we can do something, by an 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’d be interesting to check that. So, that you’re going to have to use medical doctors with, but it sounds interesting to me.”

The comments were immediately slammed by scientists, who said the president was endangering the public’s health.

Mr. #Trump, chlorine disinfectants are poison. I know chemistry isn't your strong suit. Or biology. Or physics. Or reality. UV light kills viruses, but shined on human cells in the way you seem to say causes mutations. Barron, at 14, has likely had a science class & can explain. https://t.co/rfR8WQpvNp — Laurie Garrett (@Laurie_Garrett) April 24, 2020

This 👇🏼 – injecting lethal carcinogens into lungs – as Rx suggestion from US leadership – clinches the spot for most depressing thing today Could’ve been failed remdisivir RCT

OR

Only 21% sampled NYC residents being antibody +ve for #COVID19 in a city already overwhelmed by it pic.twitter.com/0nbeA6P7Yo — Rohan Khera (@rohan_khera) April 24, 2020

On Friday, Trump said that he was being sarcastic when he raised the possibility of injecting disinfectant inside people’s bodies to fight coronavirus.

The Guardian newspaper reported later on Friday that the leader of a group that has been peddling industrial-grade bleach as a treatment for the coronavirus wrote to Trump this week, saying that chlorine dioxide “can rid the body of COVID-19”.

It is unclear whether the letter or efforts by similar groups influenced Trump’s comments on Thursday. The White House did not immediately comment on the report.

Trump has previously touted unproven treatments as cures for COVID-19, the disease caused by the coronavirus, despite caution among health officials.

A man in Arizona died in late March after taking chloroquine phosphate – a substance used to clean fish tanks – after Trump repeatedly talked about hydroxychloroquine. The man’s wife told TV network NBC News he had been watching the president’s daily briefings.

Lysol and Dettol maker Reckitt Benckiser (RB.L) warned people against using disinfectants to treat the coronavirus.

“Under no circumstance should our disinfectant products be administered into the human body (through injection, ingestion or any other route),” the company said in a statement.

Heat, humidity

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

“The virus dies quickest in the presence of direct sunlight,” he told the briefing in findings that raised hopes the coronavirus would mimic the behaviour of other respiratory diseases such as influenza, which are typically less contagious in warm weather.

But the coronavirus has also proven lethal in warm, humid countries such as Singapore, raising broader questions about the effect of environmental factors.

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 weakened organism strength dropped to six hours and when the virus was exposed to high humidity and sunlight, it 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.