How can inflammatory bowel disease cause appendicitis? My friend had appendicitis and his doctor said it was probably because of his ibd. If appendicitis is an infection, how can ibd cause it?

Inflammation. Appendicitis is inflammation of the appendix, which can be caused by by inflammatory bowel disease. Appendectomies used to be done to prevent future confusion over abdominal pain.
Related. Causative? Appendicitis is just "inflammation of the appendix." ibd is an inflammatory disease and can certainly cause this. It would be unlikely that it affected only the appendix. Inflammation from ibd could break down natural barriers to bacteria and cause obstruction of the appendix which could lead to traditional bacterial infection.