Don't confuse the odor of smoke with the particulants in the air from smoke. A smokey odor doesn't harm someone with CF and can stick around long after actual smoke particulants are gone. I inherited some books of my parents who died 10 years ago. The books haven't been near smoke since then but they still smell. Same is true of fabric which acts like a sponge for odors.
Everyone needs to do what they think is best for their kids. Still it's nice to do it based on some scientific/factual basis and not just on emotion.
Which is why I think even if the friend's parents DO smoke in the house (and you don't know yet that they do), then if they agree to really air the house out before your son comes over and not smoke in the house while he's there, your son would be OK. If you say your son can't ever go to his friend's house, you're basically saying he has to give up this friendship. A friendship needs give and take and if he can never do things with his friend and his family, well.....
Everyone needs to do what they think is best for their kids. Still it's nice to do it based on some scientific/factual basis and not just on emotion.
Which is why I think even if the friend's parents DO smoke in the house (and you don't know yet that they do), then if they agree to really air the house out before your son comes over and not smoke in the house while he's there, your son would be OK. If you say your son can't ever go to his friend's house, you're basically saying he has to give up this friendship. A friendship needs give and take and if he can never do things with his friend and his family, well.....