5 NIH studies from 2004-2020 all finding verifiable health effects from wearing a face mask, including scientifically verified reduction is blood oxygen level:
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mask studies on efficacy
https://pubmed.ncbi.nlm.nih.gov/29395... https://pubmed.ncbi.nlm.nih.gov/32590... https://pubmed.ncbi.nlm.nih.gov/15340... https://pubmed.ncbi.nlm.nih.gov/26579... https://pubmed.ncbi.nlm.nih.gov/31159...
SOME of the mask studies on efficacy: https://www.medrxiv.org/content/10.11... https://www.medrxiv.org/content/10.11... https://www.nejm.org/doi/full/10.1056... https://jamanetwork.com/journals/jama... https://www.cmaj.ca/content/188/8/567 https://www.ncbi.nlm.nih.gov/pmc/arti... https://pubmed.ncbi.nlm.nih.gov/19216... https://aaqr.org/articles/aaqr-13-06-... https://www.ncbi.nlm.nih.gov/pmc/arti... https://academic.oup.com/cid/article/... https://www.jstage.jst.go.jp/article/... https://link.springer.com/article/10.... https://www.journalofhospitalinfectio... https://www.ncbi.nlm.nih.gov/pmc/arti... https://www.cidrap.umn.edu/news-persp... https://www.nap.edu/read/25776/chapte... https://wwwnc.cdc.gov/eid/article/26/... https://academic.oup.com/annweh/artic... https://www.ncbi.nlm.nih.gov/pmc/arti... https://www.acpjournals.org/doi/10.73...
