Fact check: No evidence linking masks to oral bacteria and to lung cancer; article refers to study that did not involve masks

Users on social media are sharing an article that claims long-term mask-wearing “breeds microbes that infiltrate the lungs and contribute to advanced stage lung cancer”. As alleged evidence, the article refers to a study that did not involve mask-wearing and does not makes this claim. The authors of the study say that there’s no scientific evidence to back the article’s misinterpretation of their actual results.

Reuters Fact Check. REUTERS

The article ( here ) was published by Natural News, a website that according to reports by Vox ( here ) and McGill University’s Office for Science and Society ( here ) is known for spreading conspiracy theories and false health information. In May 2020, the site was banned by Facebook for violating its “community standards on spam”  ( here ).

A Facebook post with a screenshot of the article and its text can be seen here .

To support the claim that “masks are priming the lungs for inflammation and lung cancer pathology”, the article refers to a study published in February 2021 in the American Association for Cancer Research (AACR) journal Cancer Discovery that can be seen here .

However, this study does not mention mask-wearing. According to the AACR   here , the study found that the “enrichment of the lungs with oral commensal microbes was associated with advanced stage disease, worse prognosis, and tumor progression in patients with lung cancer.” 

Two of the authors of the study told Reuters that their study does not involve studying mask-wearing, and that “currently there is no scientific evidence to this misinterpretation of our result.”

Dr James Tsay ( here ), Assistant Professor at the Department of Medicine at NYU Grossman School of Medicine, told Reuters via email that the patients were all recruited years before the pandemic, “between 2013-2018.” Tsay said that “since mask-wearing was not common during our study period, it is highly unlikely it is one of the reasons that contribute to our findings.”

Another author of the study, Dr Leopoldo N. Segal, Assistant Professor at the Department of Medicine at NYU Grossman School of Medicine ( here ), told Reuters via email that: “There is no scientific rationale to suspect that mask wearing will increase the amount of oral bacteria that reach to the lung.”

Segal explained that “the main source of these bacteria to the lung is the mouth and oropharynx [the part of the pharynx that is behind the mouth] itself.” The amount of these oral microbes is dependent on oral hygiene and food intake. Generally, “they are going to be in the oral cavity of pretty much every individual.”

The authors of the study told Reuters they have “many different hypotheses as to why level(s) of these microbes can be detected in the lung” such as “an aspiration of our own oral secretions” or a “decreased ability to clear them.”

Other experts contacted by Reuters agreed.

Dr Alison Morris, Chief of the Division of Pulmonary, Allergy and Critical Care Medicine at University of Pittsburgh Medical Center and professor at the University of Pittsburgh School of Medicine ( here ) told Reuters via email that: “There are no studies linking mask-wearing to changes in the oral microbiome” and that there’s no data to show masks “make those microbes more likely to end up in the lung.” She said that “one could argue that masks may decrease the risk of cancer since they make it harder for people to smoke.”

Dr William Nelson, director of the Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins ( here ), also said that the bacteria referred to in the study are normally present in the oropharynx ( here ). “The best strategy for lung cancer prevention remains smoking cessation,” he added.  

Reuters has previously debunked the claim that mask-wearing can cause cancer due to oxygen deficiency ( here ). Reuters also debunked claims falsely linking the wearing of masks to other severe illnesses such as pleurisy, fungal infections and hypercapnia, visible  herehere  ,  here  ,  here  and  here  .

Health authorities like the Centers for Disease Control and Prevention and the World Health Organization recommend the use of face masks as one of several protective measures that help slow the spread of SARS-CoV-2 ( here , here ).


False. Misleading article misinterprets the results of a study about an increased presence of oral commensal microbes in the lungs and lung cancer and that did not include mask-wearing. Authors of the study in question contacted by Reuters say there is no scientific evidence to claim masks will increase the amount of oral bacteria that reach to the lung.

This article was produced by the Reuters Fact Check team. Read more about our work to fact-check social media posts  here  .