"secure the mask according to manufacturer’s instructions and avoid touching the mask once it is applied" [ https://www.journal.acorn.org.au/cgi/viewcontent.cgi?article=1105&context=jpn ].
Every idiot I've seen in public has their hands all over their mask, taking it on and off, hanging it around their neck, putting it in their pocket. Ask any professional surgeon if they do that in the operating room! LOL