Diarrhoea—defined as passing looser or more frequent stools than is normal for you—is something everyone experiences at some point. While often a short-lived inconvenience caused by a “stomach bug,” it can sometimes be a signal from the body that something more serious is happening. In the UK, it remains one of the most common reasons for GP consultations.
Diarrhoea is the body’s way of reacting to an imbalance in the digestive system. It occurs when the intestines either push contents through too quickly for water to be absorbed, or when the lining of the bowel becomes inflamed and “leaks” fluid into the stool.
The most common cause of sudden diarrhoea is gastroenteritis, often triggered by viruses like norovirus or rotavirus. These are highly contagious but usually self-limiting, meaning the body clears the infection on its own within a few days without the need for antibiotics.
The biggest risk associated with diarrhoea is dehydration, especially in children and the elderly. When you have diarrhoea, you lose vital salts and electrolytes as well as water. Using oral rehydration sachets (like Dioralyte) is often more effective than plain water alone, as they contain the precise balance of glucose and salts to help the body absorb fluid.
If diarrhoea is severe, contains blood, or is accompanied by a high fever, it may be bacterial food poisoning (such as Salmonella, Campylobacter, or E. coli). This usually occurs from eating undercooked meat or food prepared in unhygienic conditions. Unlike viral bugs, bacterial infections can sometimes require medical intervention.
Medications like Loperamide (Imodium) work by slowing down the movement of the gut muscles. While helpful for managing symptoms during travel or an inconvenient flare-up, they should be used with caution if you have a high fever or bloody stools, as they can sometimes “trap” a bacterial infection inside the bowel.
Ironically, taking antibiotics for an unrelated infection (like a chest or urinary tract infection) can trigger diarrhoea. Antibiotics can wipe out the “friendly” bacteria in your gut, allowing “bad” bacteria like Clostridium difficile (C. diff) to overgrow and cause significant bowel inflammation.
Chronic diarrhoea is often linked to the body’s inability to digest certain substances. The most common examples are lactose intolerance (dairy) and fructose malabsorption (fruit sugars). In these cases, the undigested sugars draw water into the bowel, leading to urgency and loose stools.
In a confusing twist, some people experience diarrhoea because they are actually severely constipated. This is known as overflow diarrhoea. A large, hard mass of stool becomes stuck in the rectum, and only watery, liquid stool can leak around the blockage, mimicking a standard bout of diarrhoea.
The “fight or flight” response releases hormones like adrenaline that can speed up the digestive system. This is why many people experience “nervous diarrhoea” before an exam or a big presentation—the brain is essentially telling the gut to empty itself to prepare for a perceived threat.
While most diarrhoea clears up in a few days, a prolonged change in bowel habit—defined as loose stools or going more often for three weeks or more—must be taken seriously. This is a primary symptom of colorectal (colon) cancer. If the bowel habit doesn’t return to your normal, it requires urgent investigation.
MyHSN Top Tip: If you are over the age of 50 or have a family history of bowel issues, never ignore a change in your bowel habits that lasts longer than three weeks. While it is often something less serious like IBS or a food intolerance, it can be an early sign of colon cancer, which is much easier to treat when caught early.
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