To answer your question...yes, sadly, I have used one before. I used to commute to work in downtown Toronto and found that I was coughing up a lung after a couple of months of riding. After using the mask for a couple of weeks it was no longer a problem though. Sucks (pardon the pun) getting used to riding with it as it is much more difficult to breathe. I agree with Maelstrom....but sadly sometimes you have no choice