Inhaling steam could reduce viral load and speed up recovery from COVID-19, but it might only work for a small number of people with access to regular testing, according to a new peer-reviewed scientific study from Italy.
"This simple approach ... might help easing the consequences of Sars-CoV-2 infection, if applied early in at-risk individuals in whatever healthcare setting, especially in low-income countries with limited access to equipped hospitals or intensive care units," said the team led by Dr Giancarlo La Marca with the University of Florence in a paper published in the journal Life Sciences on Saturday.
The researchers qualified their findings, saying the results were preliminary because of the small scale of the experiment. The method also needed to be applied at the very early stage of infection, when the patient might not even be aware of having the virus, they said.
Heat appears to be a factor in the stability of the coronavirus. Its genes are in single-stranded ribonucleic acid with a relatively unstable structure that breaks down easily in a hot environment.
Some studies have also found that the virus's spike proteins tend to point inward and bind less easily with host cells as temperatures rise.
La Marca's team wanted to see if heat could be used to fight the pandemic.
They recruited 10 doctors and nurses immediately after they were found positive in routine testing programs.
The volunteers put their face over steaming water with a towel over their head for four minutes, five times in an hour for four days in a row. The temperature of the steam was 55-65 degrees Celsius (131-149 degrees Fahrenheit).
Seven patients tested negative after the first day of steam inhalation, and the results were confirmed by four consecutive swabs. None of the seven had any medication or other treatment.
The three other patients had some complications such as an allergy or they were taking hydroxychloroquine.
Analysis of swabs showed rapid decline in viral load counts for nearly all patients during the treatment.
None of the patients progressed to a severe condition, with their body clearing the virus within days, the researchers said.
Steam has been a home remedy to relieve colds in many parts of the world. In Britain, 80 per cent of general practitioners have recommended steam inhalation for their patients, according to a survey in 2016.
But whether steam should be considered a potential coronavirus therapy has prompted some vigorous debate.
In May, a group of paediatricians in the British city of Birmingham published a letter in The Lancet medical journal saying the number of children with burns increased 30 times after the coronavirus outbreak, and most came from homes using steam therapy.
The accidents happened when a child knocked over a bowel or kettle of boiling water, with some of the children just two weeks old, the paediatricians said.
"Clinicians should actively discourage steam inhalation and educate parents about alternative treatments for their child," the team led by Dr Colin Brewster said in the letter.
The Italian team acknowledged the potential danger to children.
They also acknowledged that the steam could not reach the lower parts of the airway such as the bronchial tree and lungs, where most of the virus tends to concentrate in the later stages of infection. But they argued that the positive results of their experiment should not be overlooked.
"Our small study suggests that a protocol based on cycles of steam inhalation at temperatures of 55-65 degrees Celsius might indeed be beneficial," they said in the paper.
In the late 1960s, French biologist Andre Lwoff discovered that the rhinovirus, a major cause of the common cold, struggled to replicate after being exposed to a temperature of 43 degrees Celsius for half an hour.
Opinion in scientific literature since 1999 on the effectiveness of steam inhalation on colds appears evenly divided, with no evidence of either benefit or harm.
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