Ulcerative Colitis (UC) is a chronic form of Inflammatory Bowel Disease (IBD) that causes continuous inflammation and ulcers in the inner lining of the large intestine, or colon. The presence of this inflammation directly impacts the colon’s function, with changes in the appearance and frequency of bowel movements being one of the most common and telling indicators of disease activity. Observing these alterations in stool is often the first sign that the condition is active, known as a flare-up.
The Distinctive Appearance of Ulcerative Colitis Stool
Rectal bleeding is a hallmark symptom of an active UC flare-up. The blood typically appears bright red, either mixed into the stool, as streaks on the surface, or occasionally passing on its own as a bloody discharge. This bright color indicates the blood is fresh, originating from the lower part of the large intestine or the rectum.
Stool often contains an excessive amount of mucus or pus. This substance may appear jelly-like and clear, or cloudy and mixed with pus, which is a sign of the body’s inflammatory response occurring directly on the colon’s surface. The overall consistency of the stool is usually loose, soft, or entirely watery, corresponding to a Type 6 or Type 7 on the Bristol Stool Chart.
The experience of passing stool is also altered, involving a high frequency of bowel movements that is often accompanied by an intense sense of urgency. During a moderate to severe flare, a person may have six or more movements per day, and in extreme cases, more than ten. Patients frequently experience tenesmus, which is the persistent, painful sensation of needing to pass a bowel movement, even immediately after having done so, often resulting in the passage of only small amounts of blood, mucus, or liquid.
The Inflammation Behind the Change
The visual characteristics of UC stool are a direct consequence of the inflammatory process limited to the colon’s innermost lining, the mucosa and submucosa. UC causes diffuse friability and superficial erosions, or ulcers, to form on this lining. These fragile, open sores are the source of the bleeding, as the passage of stool causes mechanical abrasion against the damaged tissue.
The inflammation also severely compromises the colon’s ability to perform its primary function: reabsorbing water and electrolytes. When the lining is inflamed, it cannot effectively absorb minerals like sodium and chloride, and water is consequently pulled out of the bloodstream and into the colon, resulting in the characteristic watery diarrhea. The excessive mucus observed is largely an inflammatory exudate, a mixture of pus, shed epithelial cells, and inflammatory white blood cells, which are mobilized to the site of damage.
The intense urgency and tenesmus are caused by inflammation, specifically when it involves the rectum (proctitis). Inflammation in this final segment of the colon makes the rectal wall swollen and highly sensitive, causing the nerves to misinterpret the presence of gas or a minimal amount of liquid stool as a full rectum requiring immediate and forceful evacuation.
Monitoring Stool Appearance and Seeking Medical Guidance
The goal of treatment is to return the stool to a more normal consistency, such as Bristol Stool Chart Type 3 or 4, and eliminate the presence of blood and mucus. During periods of remission, the stool should resemble that of a person without UC, though consistency can still fluctuate based on diet and hydration.
Any change in bowel habits, particularly a sudden increase in frequency or the appearance of blood and mucus, should be reported to a healthcare provider, as this often signals a flare that requires adjustment to medication. Certain “red flag” symptoms warrant immediate medical consultation because they may indicate a severe or life-threatening complication. These signs include passing multiple, entirely bloody stools per day, the presence of a high fever, or any signs of severe dehydration, such as dizziness, excessive thirst, and reduced urination.