In a recent European study, active smoking was found to be a risk factor for Crohn's Disease. The results also suggest that exposure to secondhand smoke is a risk factor. In ulcerative colitis, active smoking shows dose-dependent beneficial effects. It is thought that the nicotine in cigarettes affects the smooth muscle and motility inside the colon. Some studies are looking at the effect of nicotine patch on persons with active disease. A person with ulcerative colitis, absolutely, should not start to smoke. Risks of smoking far outweigh any possible benefit.