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Several environmental factors have been associated with IBD, these include:

  • Microorganisms
  • Hygiene hypothesis
  • Smoking
  • Oral contraceptive pill


  • There is increasing evidence to suggest that the immune response to intestinal microorganisms is important in the pathogenesis of IBD
  • The distal ileum and colon contain high concentrations of bacteria (more than 10 million million organisms/gram)
  • Many studies have shown that the body's response to these microorganisms can initiate IBD and/or continue disease. There is ongoing research in this area

Hygiene hypothesis

  • The premise of the hygiene hypothesis is that lack of childhood exposure to microorganisms changes the way the body responds to these microorganisms when exposed later in life
  • This may explain the increasing incidence of IBD in some communities in the developed world.
  • There is ongoing research in this area


  • Active smokers are at an increased risk for acquiring Crohn's disease.
  • So if you have Crohn's disease, the best thing you can do for your disease is to stop smoking. If a smoker with ulcerative colitis stops smoking, they can experience a flare of their ulcerative colitis
  • Doctors certainly do NOT advocate smoking to maintain ulcerative colitis remission as the harm from smoking is substantial

Oral contraceptive pill

  • There is a slight association (about a two-fold risk) between oral contraceptive use and the development of Crohn's disease, but not ulcerative colitis


If you are interested in other gastrointestinal-focused information and intervention websites developed and hosted at
Swinburne University of Technology,
please go to:

IBSclinic.org.au for individuals with Irritable Bowel Syndrome

Gastroparesisclinic.org for individuals with Gastroparesis


This website and its content is not intended or recommended as a substitute for medical advice, diagnosis or treatment. Always seek advice of your own physician or other qualified health care professional regarding any medical questions or conditions.

© 2014 Swinburne University of Technology | CRICOS number 00111D