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| 1937 || || || During the {{w|Second Sino-Japanese War}}, face masks become essential protection against chemical and biological warfare.<ref name="sixthtone.comt">{{cite web |title=A Brief History of Face Masks in China |url=https://www.sixthtone.com/news/1005177/a-brief-history-of-face-masks-in-china |website=sixthtone.com |accessdate=18 September 2020}}</ref> || {{w|China}}
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| 1937 || || || Study by Hart and Davis confirms the value of face masks in preventing infection of surgical wounds.<ref name="Spooner"/><ref name="Spooner"/> ||
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| 1948ā1950 || || || After a period of decline since the end of the Spanish flu, the use of face masks quickly becomes common again during several major flu outbreaks around this time.<ref name="sciencenorway.no">{{cite web |title=Face masks: Why do different countries in the world have such different recommendations? |url=https://sciencenorway.no/cultural-history-disease-health/face-masks-why-do-different-countries-in-the-world-have-such-different-recommendations/1689385 |website=sciencenorway.no |accessdate=11 September 2020}}</ref> ||
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| 1958 || || || "In 1958 Kiser and Hitchcock reported report on a mask that combined combines the deflection and filtration princip1es.lā This was a plastic mask that diverted diverts the flow of breath backward on either side. Filter material near the side outlets was is designed to trap the deflected organisms."<ref name="Spooner"/> ||
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| 1958 || || || Andersen develops a sampling chamber to collect airborne particles in several categories of decreasing particle size.<ref name="Spooner"/> ||
