I use 505 and really like it. I also have asthma and it normally doesn't bother, even when I would use it indoors. However, I used it the other day and have had some very bad asthma spells, as I call them. I have had to use my rescue inhaler several times a day since. Not sure if it was the 505 or all of the leaves/dust blowing outside in the wind lately. If you are concerned about possible health risks, (ie. asthma, COPD, etc.)I would use a disposable face mask. You could probably get them at a pharmacy or even hardware store.