I don't have to wear a mask if I don't want to with my COPD, asthma etc so I make sure I carry an alert card with me and my pump(s) (asthma, COPD) just in case I am stopped by the police but funny enough I wear a mask but if the weather is hot by wearing a mask it makes it a lot harder for me breathing wise so I remove it.
Funny thing yesterday I was standing outside Tescos with my mask down just under my chin waiting for a taxi, a police car pulled out and 2 coppers got out to go inside Tescos, one of them looked at me with my mask around my neck and then stopped and said to his side-kick "Oh...hang on..." and he went back to his car and got 2 masks and they both put them on, I quipped in with a smile "You both should get asthma & COPD like me and you wouldn't have to wear a mask" they both just laughed and kept walking.