Three are imoprtance reasons of colitis.

Genetically.
As many and other autoimmune diseases are lupus,rheumatism, asthma is genetically predisposition having, and acutings provoking of physical over loads.tress, injuries, gastroanteral diseases.

Disbacteriosis is bad natural gastrointestinal flora disordered, in bowel living a non needing micro flora, as producing toxins, and damaging bowel s cells.

Autoimmune disorders.
Allergy is on the proteins, causing an especial and harmful antibodies,damaging not an organism s enemies, but cells of mucus intestine thick.