The absence of grooves in thick stools and the presence of grooves in thin stools may be due to ulcerative colitis, intestinal tumors, hemorrhoids and other causes. 1. Ulcerative colitis: In patients with ulcerative colitis, the mucous membrane in the intestines is thickened and disordered, resulting in intestinal dysfunction, which leads to the absence of grooves in coarse stools and grooves in fine stools. 2. Intestinal tumor: in patients with intestinal tumor, the tumor occupies and proliferates in the intestinal tract, resulting in the absence of grooves in thick stools and grooves in thin stools. 3. Hemorrhoids: in patients with internal hemorrhoids, the hemorrhoids oppress the stool, thus there is no groove when the stool is coarse and there is a groove when it is fine. There are many other reasons for the lack of grooves in the stools and the grooves in the fine ones, so patients should consult a doctor in time, improve the relevant examinations to clarify the cause of the disease, and then be treated under the formal guidance of the doctor.