It's a matter of terminology; ‘mask’ has a narrower meaning than in colloquial use. https://www.cdc.gov/niosh/npptl/pdfs/UnderstandDifferenceInfographic-508.pdf

It's a matter of terminology; ‘mask’ has a narrower meaning than in colloquial use. https://www.cdc.gov/niosh/npptl/pdfs/UnderstandDifferenceInfographic-508.pdf https://www.cdc.gov/niosh/npptl/pdfs/UnderstandDifferenceInf... (Compounding the confusion is that a reusable rubber respirator is also called a ‘half mask’.)