Ulcerative colitis (UC), or ulcerative colon, was first described by Willks and Moxon in 1875, named ulcerative colitis by Willks and Boas in 1903, and officially named chronic nonspecific ulcerative colitis by the International Organizing Committee for Medical Sciences of the World Health Organization (WHO) in 1973. It is a chronic nonspecific inflammatory disease that mainly affects the mucosa of the colon, often starting in the left hemocolon and progressing to the proximal colon or even the whole colon in a continuous manner. Clinical symptoms vary in severity and may alternate between remission and exacerbation, and patients may have only colonic symptoms or systemic symptoms.