What does your poop actually say about you?

Clostridioides difficile (C. diff) infection produces watery diarrhoea (Bristol Type 6-7) that is often described as having a distinctive foul, sweet, or "horse barn" odour. The stool is typically greenish-yellow and may contain mucus. C. diff diarrhoea occurs at least 3 times per day and is persistent. It almost always occurs after antibiotic use, which disrupts normal gut flora. If you are experiencing watery diarrhoea that started during or within 8 weeks of an antibiotic course, contact your doctor for a stool toxin test. (Source: IDSA/SHEA Clinical Practice Guidelines for C. difficile Infection)

Diverticulitis does not produce a single characteristic stool type. During an acute flare, constipation (Types 1-2) is more common than diarrhoea. The hallmark symptoms are left-sided lower abdominal pain and fever, not a specific stool appearance. Diverticular bleeding (a related condition) can produce significant bright red or maroon-coloured blood in the stool with no pain. Diverticulosis is present in approximately 50% of adults over 60 and 70% of those over 80, with the vast majority having no symptoms. (Source: AGA Clinical Practice Guidelines on Diverticulitis, 2021)

Floating stools are caused by gas trapped within the stool, and in most cases this is completely benign. High-fibre diets, legumes, and carbonated beverages all increase gas production in the colon. The widespread belief that floating stool indicates fat malabsorption (steatorrhoea) is a medical myth in the vast majority of cases. A landmark 1972 NEJM study (Levitt and Duane) demonstrated that floating stools are caused by gas content, not fat content. True steatorrhoea is characterised by stools that are pale, greasy, foul-smelling, and difficult to flush. Approximately 10-15% of adults regularly produce floating stools. (Source: Levitt MD, Duane WC. NEJM 1972; Wang et al. 2023)

Black stools have two very different categories of cause. The benign category includes iron supplements (most common), bismuth subsalicylate (Pepto-Bismol), black liquorice, and blueberries in large quantities. These produce black but normal-consistency stools. The concerning category is melena: tarry, sticky, shiny black stools with a distinctive foul odour, caused by digested blood from an upper gastrointestinal bleed such as a stomach ulcer. Melena looks and smells distinctly different from supplement-related black stool. If your stool is black, tarry, sticky, and foul-smelling without an obvious medication or dietary explanation, seek urgent medical attention. (Source: Gralnek et al. 2014, Am J Gastroenterol)

A small amount of mucus in stool is completely normal. The intestinal lining produces mucus continuously as a lubricant, and occasionally this is visible, especially with softer stools. Approximately 5-10% of adults notice visible mucus from time to time. Increased mucus can occur with dietary changes, mild infections, or stress. IBS is the most common chronic cause and mucus is one of the supporting Rome IV diagnostic criteria for IBS. More significant mucus, particularly if blood-streaked, accompanies persistent diarrhoea, or occurs with weight loss, can indicate inflammatory bowel disease. The key distinction is between occasional mucus (very common, almost always benign) and a new pattern of frequent, blood-streaked, or large-volume mucus, which warrants investigation. (Source: Rome IV criteria; Palsson et al. 2020)

The Bristol Stool Form Scale was developed by Dr Stephen Lewis and Dr Ken Heaton at the University of Bristol, published in 1997. It classifies stools into seven types based on form, from Type 1 (hard separate lumps) to Type 7 (entirely liquid). The scale was created because patients and doctors had no shared vocabulary for describing stool consistency, making clinical assessment unreliable. The scale correlates strongly with colonic transit time: Type 1 indicates slow transit with excessive water reabsorption; Type 7 indicates rapid transit with minimal water absorption. Types 3 and 4 represent the optimal transit time of approximately 18-36 hours. The scale is now used globally in clinical practice and appears in the Rome IV diagnostic criteria for IBS. (Source: Lewis SJ, Heaton KW. Scand J Gastroenterol. 1997;32(9):920-924)

Day-to-day variation in stool type and colour is completely normal. Most healthy adults vary by 1-2 types across a typical week. Colour variation follows diet closely: meals heavy in leafy greens, beetroot, or iron-rich foods produce visible colour changes within 12-36 hours. The clinical concern is not variation itself but persistent unexplained change. If your stool type shifts from your personal baseline and stays there for more than three weeks without an obvious dietary explanation, that is worth discussing with a healthcare provider. Similarly, a sustained colour change, particularly to pale, black, or red without a dietary cause, warrants attention. Population data shows most adults experience at least one unusual stool per month, making occasional variation one of the most normal things about digestion. (Source: Rome IV criteria; Wang et al. 2023)

Pale, grey, or clay-coloured stools indicate a lack of bile in the stool. Bile, produced by the liver and stored in the gallbladder, is responsible for the brown pigmentation of normal stool via the breakdown product stercobilin. A blockage in the bile ducts (from gallstones, a stricture, or, less commonly, a tumour), liver disease, or a condition affecting the gallbladder can all reduce bile flow and produce pale stools. A single pale stool after a meal very low in fat is usually benign. Persistent pale or clay-coloured stools, especially if accompanied by dark urine, yellowing of the skin or eyes, or upper right abdominal pain, warrant urgent medical evaluation. Do not wait more than 2-3 days before seeing a doctor if pale stools persist. (Source: NICE CKS; NHS clinical guidance)