Researchers discovered there was no statistically meaningful difference in the number of people who contracted the virus in a group using masks in public as opposed to a group that did not do so.
The team, from Copenhagen University Hospital, says the conclusions should not be used to fight against their widespread use because masks block people from infecting others.
It appears just days after the Centers for Disease Control and Prevention updated its guidelines, saying masks guard the wearer just as much as their surroundings.
The study, which was published in the Annals of Internal Medicine, was carried out in April and May when Danish officials did not advise wearing face masks.
Throughout this period, only approximately two percent of Denmark's population had contracted the coronavirus, lower than many other European countries such as Spain and Italy.
The team got more than 6,000 adults in the research and split them into two groups: one using surgical masks in public coverings and one control group that did not. Results revealed that, after one month, 1.8 percent of the people using masks had been infected with the virus.
By comparison, 2.1 percent of the people in the unmasked group got the virus. Meaning that the difference between the two groups is not statistically notable. 'The study does not confirm the expected halving of the risk of infection for people wearing face masks,' the authors wrote in a press release.
'The results could indicate a more moderate degree of protection of 15 to 20 [percent], however, the study could not rule out that face masks do not provide any protection.'
Previous researches have revealed similar conclusions, arguing that masks provide only poor protection for the person wearing it, but can dramatically decrease the risk to others if the wearer is infected, even when showing no symptoms. Stopping the spread to others is recognized as source control.
But many experts object and say they are flaws to the study such as the authors not independently checking mask use or that users wore them correctly. 'There is absolutely no doubt that masks work as source control,' Dr Thomas Frieden, a past director of the CDC, who wrote in an editorial.
'The question this study was designed to answer is: Do they work as personal protection? An N95 mask is better than a surgical mask. A surgical mask is better than most cloth masks. A cloth mask is better than nothing.'
Last week, the CDC renewed its guidelines saying that masks shield wearers from catching COVID-19, not just those around them.
Health officials said cloth masks block droplets from being breathed by the wearer and further provide 'filtration for personal protection' by preventing droplets from reaching others.