Smoking is one of the environmental risk factors linked to IBD.  However, the relationship between smoking and inflammatory bowel disease remains a source of confusion and controversy. Smoking is negatively associated with ulcerative colitis but positively associated with Crohn's disease. These differences have been the subject of much interest and scrutiny with the hope that they may offer some insight into the pathogenesis of the two conditions and possibly lead to alternative therapeutic options.  Researchers suspect that this finding may be due to the release of a protective factor (the steroid-sparing effect of nicotine) in smokers who are susceptible to ulcerative colitis.


In Crohn’s disease, smoking cigarettes has been shown to have detrimental effect. People who smoke, or who have smoked in the past, have a higher risk of developing Crohn's disease than non-smokers. Crohn's Disease patients that smoke have more relapses, repeat surgeries, and may require aggressive immunosuppressive treatment. People with Crohn's Disease are strongly encouraged by their physicians to stop smoking in order to prevent flare-ups of the disease.