I have chemical sensitivity, it's awful. It isn't the same as what people with allergies seem to experience or describe. I feel like I can't breath, the front of my face above my eyes and nose feel uncomfortable or even hurt. Almost anything that comes from an aerosol can, spray paint, some so called disinfectants, things like WD40, insecticides such as Raid and insect repellants. One of the worst is some apparently common ingredient in many perfumes and colognes. I can detect the presence of that chemical outside from many yards away. If I'm in a room and someone comes in with it I have to leave.
It may be also psychosomatic to some degree I suppose but mostly it is actual. Degree of symptoms is proportional to the amount of exposure. However I have on many occasions experienced symptoms when the actual exposure was so small I didn't even smell it, well actually describing it as a smell isn't completely accurate. One time at an outdoor party I started getting sick and found out later someone on the other side of the house had sprayed insect repellent. Once at a meeting I had shook hands with someone I was introduced to before going in. After the meeting started I began feeling like I couldn't breath, soon I figured out there was something on my hand. I went to the bathroom but it wouldn't wash off. It was on the papers I had with me and my coffee cup. I threw it all away and drove home with all the windows down. I put a moratorium on holding hands with strangers a long time ago, just don't feel the need for physical contact, a simple nice to meet you is sufficient. As a rule if a person I meet is looks perfectly groomed, crisply pressed shirt and tie, not a single hair out of place, shiny shoes, stepping of of a $60,000 car, until I learn otherwise I regard them the same way I would a super fund site and stay as far away as possible. Maybe it's stereotypical but safe than sorry, as they say.
I don't know about the COVID or vitamin D or the mask thing as it relates to smell. I know lots of people who seem to rarely go outside anyway unless their destination doesn't have a parking garage so I don't see a big difference.