Yes, I
agree with Probiotics reply above...they actually consider smoking (including second-hand smoke) as an actual trigger for the develpment of crohn's specifically...researchers say that it's one know trigger for CD...of course that likely doesn't mean it's every CDers trigger.
I have crohn's colitis (my CD was affecting my small intestines as well for the first few yrs when I became sick, as well as my colon, rectom and anus) but when I quit smoking, my symptoms became much worse and so I started again, but smoke only 6 cigs/day...luckily my CD still has not affected my small intestines again considering I am still a smoker.
IBD is such a weird and nasty disease.
Here's a link regarding the carbon monoxide and inflammation in the colon....
http://www.sciencedaily.com/releases/2006/01/060103084934.htm