Yes IBS can cause thinner stools and yes I have had that same issue. My doctor put me on Fibercon to make them bulkier. I understand the whole colon cancer thing becuase of the blood, but here's a good way to look at that. After you have a BM, if you were to pat your self with the paper, is there blood? If you get blood simply from patting the area then yes I would address it. If you are WIPING the area continuously becuase of anxiety then you may be causing the bleeding. Note the difference and unfortuntely welcome to the world of IBS.