US scientists claim they've developed an oral antiseptic spray that kills 99.9 percent of infectious airborne germs that cause colds and the flu.
But Australian experts warn there is a lack of clinical evidence to prove how effective it is.
Researchers from the San Francisco University Hospital say the Halo Oral Antiseptic is the first product of its kind and uses glycerine, xanthan gum and cetylpyridinium chloride (CPC) to fight respiratory illnesses.
When tested in a laboratory, the scientists said it showed anti-infective activity in cell culture experiments. People who used three sprays of Halo were protected from breathing in airborne germs for up to six hours, even when eating and drinking.
"The glycerine and xanthan gum prevent the germs from entering a person's system and the CPC kills the germs once they're trapped there," said study author Dr Frank Esper in a media release.
However Dr Alan Hampson, chairman of the Influenza Specialist Group, says more comprehensive studies need to be done.
"What they have done is show in a laboratory environment that you can kill influenza virus - whether they can take it any wider than that, I'm not sure," he said.
"It might be useful at times when you don't have cover against the influenza virus that is circulating and it may be useful for protecting people from common colds. But it's a long way from showing these things work in a laboratory to actually proving they work in a human environment."
Dr Hampson said widespread clinical trials would need to be conducted.
"You would take two large groups of people and give one an active oral spray and one a dummy placebo spray and monitor them through a winter's season to see if there is any difference in respiratory illness," he said.
Professor Stephen Turner, an academic in microbiology and immuniology at the University of Melbourne, also said that it is not particularly revolutionary.
"The interesting thing is it appears to be an anti-infective that can be sprayed into the mouth and upper airways –– as such, it is not that different to other antiseptics, such as gargling Betadine, but is easier to deliver," he said.
"While it may have some benefit, it is certainly no replacement for vaccination, especially for things like whooping cough and infuenza A virus, which have mechanisms that can evade these first lines of defence. Vaccination can give longer lasting protection and also help limit the spread of disease."
The researchers presented their findings at the Interscience Conference on Antimicrobial Agents and Chemotherapy.