Irritable Bowel Syndrome (IBS): This is often the most common cause of mucus in stool, characterized by a combination of abdominal pain, changes in bowel habits, and the presence of mucus without any visible blood. The presence of mucus is a hallmark symptom in some types of IBS, particularly IBS-D (diarrhea-predominant).

Infectious Gastroenteritis: Viral or bacterial infections can cause inflammation of the gastrointestinal tract, leading to the production of mucus. Symptoms often include diarrhea, abdominal cramps, and sometimes fever.
Inflammatory Bowel Disease (IBD): Conditions like ulcerative colitis and Crohn's disease can cause chronic inflammation of the GI tract, leading to mucus production. Other symptoms include bloody stools, weight loss, and abdominal pain.
Diverticulitis: Inflammation of the diverticula in the colon can cause mucus in the stool, along with symptoms like abdominal pain, changes in bowel habits, and possible bleeding.

Colorectal Cancer: Although less common, colorectal cancer can present with mucus in the stool, especially if the tumor is located in the rectum or sigmoid colon. Other symptoms may include changes in bowel habits, blood in the stool, and unexplained weight loss.
Intussusception: A condition where a part of the intestine telescopes into another part, which can cause bowel obstruction and lead to the passage of mucus and possibly blood. It's more common in children but can occur in adults, often associated with a lead point like a tumor.
Ischemic Colitis: Reduced blood flow to the colon can cause inflammation and lead to symptoms including mucus in the stool, abdominal pain, and possibly bloody stools.

Lymphogranuloma Venereum (LGV): A sexually transmitted infection caused by certain types of Chlamydia trachomatis, which can lead to proctitis (inflammation of the rectum) and symptoms like mucus discharge, pain, and bleeding.
Amyloidosis: A condition characterized by the deposition of amyloid proteins in various tissues, including the GI tract, which can lead to symptoms like diarrhea, weight loss, and possibly mucus in the stool.
Hirschsprung's Disease: A congenital condition affecting the colon, leading to severe constipation or intestinal obstruction. While primarily diagnosed in infancy, some forms may present later in life with symptoms including mucus in the stool due to chronic obstruction.