5 NIH studies from 2004-2020 all finding verifiable health effects from wearing a face mask, including scientifically verified reduction is blood oxygen level:

https://pubmed.ncbi.nlm.nih.gov/29395560/

https://pubmed.ncbi.nlm.nih.gov/32590322/

https://pubmed.ncbi.nlm.nih.gov/15340662/

https://pubmed.ncbi.nlm.nih.gov/26579222/

https://pubmed.ncbi.nlm.nih.gov/31159777/

Cloth Mask Study

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4420971/

Other Mask Studies:

https://medrxiv.org/content/10.1101/2020.04.01.20049528v1…

https://medrxiv.org/content/10.1101/2020.03.30.20047217v2…

https://nejm.org/doi/full/10.1056/NEJMp2006372…

https://jamanetwork.com/journals/jama/fullarticle/2749214…

https://cmaj.ca/content/188/8/567…

https://ncbi.nlm.nih.gov/pmc/articles/PMC5779801/…

https://pubmed.ncbi.nlm.nih.gov/19216002/

https://aaqr.org/articles/aaqr-13-06-oa-0201.pdf…

https://ncbi.nlm.nih.gov/pmc/articles/PMC4420971/…

https://academic.oup.com/cid/article/65/11/1934/4068747…

https://jstage.jst.go.jp/article/bio/23/2/23_61/_pdf/-char/en…

https://link.springer.com/article/10.1007/BF01658736…

https://journalofhospitalinfection.com/article/0195-6701(91)90148-2/pdf…

https://cidrap.umn.edu/news-perspective/2020/04/commentary-masks-all-covid-19-not-based-sound-data…

https://nap.edu/catalog/25776/rapid-expert-consultation-on-the-effectiveness-of-fabric-masks-for-the-covid-19-pandemic-april-8-2020…

https://nap.edu/read/25776/chapter/1#6…

https://wwwnc.cdc.gov/eid/article/26/5/19-0994_article…

https://academic.oup.com/annweh/article/54/7/789/202744…

https://ncbi.nlm.nih.gov/pmc/articles/PMC6599448/…

https://acpjournals.org/doi/10.7326/M20-1342