The more you sing in smoke free environments, the better you should get. Any excercise for your lungs is good, but make sure you are not near any of your triggers. I have asthma that is triggered by pollution and cigarette smoke, so I don't sit near smokers, or sing outside on the streets. Breathing excercises, taking deep breaths, and then taking that little bit extra, holding it for the count of 10, then letting it out slowly over a count of 50, control is the issue. Then, when you feel yourself going, you should be able to suppress the cough that little bit longer. Don't use your inhaler in smoky conditions if you can help it, it just opens the tubes so more nasty stuff can get in. Use it once the trigger has cleared or is clearing. Take your medication when you need to, don't think that 'I'm OK, I don't need it..' especially the Becotide inhaler (there are several brand names but they tend to be brown or green) which is the preventative but doesn't kick in until a couple of days later. The salbutamol inhaler (usually the blue ones) are 'quick fixes' and should be used as such. However, they are used by professional singers as a matter of practice, to open the tubes before going on stage.

Don't let it stop you. Keep singing at home, work, wherever... the more you do it, the longer you'll last....

Good luck and keep at it!

LTS - late onset asthma for 10 years now.