|Interesting question. I have no first hand evidence but did some research and apparently smoking cigarettes can irritate or exacerbate allergies. A reaction to urushiol oil (the compound in poison ivy plants) is an allergic reaction called allergic contact dermatitis (ACD). So it could follow that smoking cigarettes could irritate the rash more. Here's a few links for reference:
Sorry I don't have more but most of the references I found related more to other effects (positive and negative) about smoking.