Why do pilodinal cysts cause blood in stool?

They don't. : Something else is going on. See a colorectal surgeon or at least your primary care physicians. Pilonidal cysts can certainly cause a lot of problems, but jot rectal bleeding.

No, a pilonidal cyst: is external. Possible causes of blood in stool include: fissures, fistulas, hemorrhoids, cancer, ulcers, infections, inflammation, Diverticular disease & Angiodysplasia . Get evaluated if more than a one time occurrence.