1.Constipation and diarrhea can cause anal fissures. Chronic constipation can lead to hard stools and stretching of the anus, causing fissures. 

2. Anal fissures are ulcers caused by a lack of blood supply. The anal arteries are distributed on the sides, making the front and back more vulnerable to fissures. 

3.High tension in the internal sphincter muscle can also contribute to fissures. When there is stress or inflammation, the tension in the internal sphincter muscle increases, leading to fissures.