The World Health Organisation says there is "no evidence" mouthwash could protect you against coronavirus.
A report suggested mouthwash could damage the virus and prevent infection, with scientists calling for more research.
But a WHO spokesman said: "There is no evidence that using mouthwash will protect you from infection with the new coronavirus."
Researchers say studies need to be carried out into whether mouthwash can destroy the "envelope" of the virus, which stops it from replicating.
Lead author Professor O’Donnell, co-director of Cardiff University’s Systems Immunity Research Institute said: "In test tube experiments and limited clinical studies, some mouthwashes contain enough of known virucidal ingredients to effectively target lipids in similar enveloped viruses.
"What we don’t know yet is whether existing mouthwashes are active against the lipid membrane of SARS-CoV-2 (Covid-19).
"Our review of the literature suggests that research is needed as a matter of urgency to determine its potential for use against this new virus."
Researchers say mouthwash chemicals chlorhexidine, cetylpyridinium chloride, hydrogen peroxide and povidone-iodine have the potential to prevent infections.
WHO added: "Some brands of mouthwash can eliminate certain microbes for a few minutes in the saliva in your mouth
"However, this does not mean they protect you from 2019-nCoV infection."
