Why Does Diarrhea Cause Hemorrhoids to Flare Up?

Diarrhea triggers hemorrhoid flare-ups through a combination of repeated straining, chemical irritation from liquid stool, increased pressure inside the anal canal, and the sheer mechanical trauma of frequent wiping. Most people associate hemorrhoid problems with constipation, so it can feel counterintuitive that the opposite extreme causes trouble too. But the mechanisms are well-documented, and understanding them makes it much easier to manage flare-ups when a bout of diarrhea hits.

How Frequent Bowel Movements Tax the Anal Cushions

Hemorrhoids are not something you “get” the way you catch a cold. Everyone has hemorrhoidal cushions, which are pads of blood vessels, connective tissue, and smooth muscle lining the anal canal. They help with continence and act as a seal when you are not having a bowel movement. A flare-up happens when those cushions become swollen, inflamed, or displaced enough to cause pain, itching, or bleeding.

When diarrhea strikes, you might visit the bathroom six, eight, or even a dozen times in a day. Each trip involves sitting on the toilet and bearing down at least a little, and with liquid stool there is often an urgency that leads to forceful pushing. That repetition matters. Every episode of straining forces blood into the hemorrhoidal cushions while simultaneously compressing the veins that are supposed to drain them. With constipation, the problem is one long, difficult push. With diarrhea, it is many shorter pushes that add up over hours.

Research into how inflammatory bowel disease (IBD) promotes hemorrhoids has highlighted a specific version of this mechanism. Loose, frequent stools force the anal sphincter to contract repeatedly and for extended periods to maintain continence between trips. That chronic contraction raises the pressure inside the anal canal, which blocks venous outflow from the hemorrhoidal cushions. Because arterial blood keeps flowing in while venous blood cannot drain out, the cushions swell, and that engorgement can lead to bleeding and prolapse.¹ This venous congestion is one of the central reasons diarrhea and hemorrhoids go hand in hand.

Chemical Irritation from Liquid Stool

Formed stool passes through the anal canal relatively quickly and with limited direct contact against the delicate lining. Liquid stool is different. It spreads across a wider area, lingers on sensitive tissue, and carries a cocktail of substances that the anal mucosa was never designed to handle in large, repeated doses.

Digestive enzymes and bile acids are the main culprits. By the time normal stool reaches the rectum, most bile acids have been reabsorbed higher up in the gut. During diarrhea, transit speeds up so much that bile acids arrive at the lower bowel still active. These bile acids increase mucosal permeability and provoke fluid secretion, which keeps stool watery and irritating.² When that chemically aggressive fluid washes over already-swollen hemorrhoidal tissue, it inflames the surface further, heightening pain, burning, and itching. If the skin around the anus is already broken from wiping or from a previous flare, the contact stings even more.

This chemical dimension helps explain why certain types of diarrhea seem to trigger worse flare-ups than others. Bile acid malabsorption, for instance, produces a particularly caustic liquid stool. Infectious diarrhea, food intolerances, and antibiotic-related diarrhea each bring their own mix of irritants, but the underlying story is the same: liquid stool bathes hemorrhoidal tissue in substances that promote inflammation and erode the protective mucosal barrier.

Repeated Wiping Makes Things Worse

The problem does not end when you flush. Cleaning up after liquid stool requires more wiping than cleaning up after a normal bowel movement, and doing that many times a day creates significant mechanical friction. Dry toilet paper in particular is abrasive against already-irritated tissue, and the tendency to wipe harder to feel clean only compounds the damage.

A study of thrombosed external hemorrhoids found that wiping habits significantly influenced risk. People who used dry toilet paper combined with wet cleaning methods after defecation had a higher likelihood of developing a thrombosed external hemorrhoid compared with those who relied on gentler hygiene habits like regular bathing or showering.³ The same study found that regular use of a bathtub or shower and genital cleaning before sleep were associated with lower risk. The implication is clear: how you clean up after diarrhea matters almost as much as the diarrhea itself.

If you are dealing with a diarrheal illness and hemorrhoids simultaneously, switching to a bidet, a squeeze bottle of warm water, or at least unscented wet wipes (patting rather than rubbing) can reduce the friction component. This is one of the most straightforward things you can do to keep a mild flare from becoming a severe one.

The Link Between Chronic Diarrheal Conditions and Hemorrhoids

A single day of food poisoning can trigger a flare-up, but the relationship between diarrhea and hemorrhoids becomes especially clear in people with chronic diarrheal conditions. Research has found strong associations between hemorrhoidal disease and several diarrheal disorders, including ulcerative colitis, noninfectious gastroenteritis, and functional diarrhea.⁴ The pattern is consistent enough that researchers have suggested the relationship is not just coincidental but pathogenic, meaning diarrhea itself actively drives hemorrhoid development and worsening over time.

For people with IBD, this creates a frustrating cycle. The disease produces frequent, urgent, loose stools. Those stools strain the anal sphincter, congest the hemorrhoidal cushions, and irritate the surrounding tissue. The resulting hemorrhoid flare-up adds pain and bleeding on top of the diarrhea symptoms, making it harder to tell which condition is causing which symptom. Mendelian randomization research has reinforced the idea that IBD causally increases hemorrhoid risk, not just that the two happen to coexist.¹

Irritable bowel syndrome with a diarrhea-predominant pattern creates a similar dynamic, though the bowel inflammation is less severe. Even functional diarrhea, where the gut looks structurally normal but produces chronic loose stools, carries an elevated hemorrhoid risk. The takeaway is that any condition sending you to the bathroom frequently and urgently over weeks or months is loading the dice for hemorrhoid flare-ups, and managing the diarrhea itself is the most effective upstream intervention.

Inflammation Below the Surface

Beyond the mechanical and chemical insults, diarrhea may promote hemorrhoid flare-ups at a tissue level through inflammatory pathways. Emerging research has explored the connection between the gut microbiome and hemorrhoidal disease, finding that an imbalanced microbial community in the anorectal area can trigger a cascade of tissue changes. These include connective tissue breakdown, smooth muscle overgrowth, fragmentation of the elastic fibers that keep the hemorrhoidal cushions anchored in place, abnormal dilation of veins, and even vascular clotting.⁵

Diarrhea, especially when caused by infections or antibiotic use, is one of the fastest ways to disrupt the balance of gut bacteria. If the microbiome in the anorectal region shifts toward a more inflammatory profile, the local tissue becomes more vulnerable. The elastic “scaffolding” that normally supports the hemorrhoidal cushions weakens, and the blood vessels within them become more prone to swelling and clotting. This is a slower, subtler process than the immediate pressure-and-friction story, but it helps explain why people who cycle through repeated bouts of diarrhea seem to develop progressively worse hemorrhoid problems rather than just bouncing back to baseline each time.

The research here is still developing, and no one is claiming that taking a probiotic will cure hemorrhoids. But the connection between microbial imbalance, local inflammation, and tissue degradation adds an important piece to the puzzle and reinforces the idea that getting chronic diarrhea under control protects more than just comfort in the short term.

When the Problem Might Not Be Hemorrhoids at All

One practical concern worth addressing: not every bout of anal pain, bleeding, or itching during diarrhea actually comes from hemorrhoids, even if it feels like it does. The symptoms overlap heavily with other conditions. Anal fissures, which are small tears in the lining of the anal canal, are extremely common during diarrhea because of the repeated wiping and chemical irritation. Perianal abscesses can flare during diarrheal illness. And in people with IBD, ulceration of the rectal lining itself can cause bleeding that mimics hemorrhoids perfectly.

The differential diagnosis for hemorrhoid-like symptoms includes anal fissures, rectal prolapse, abscesses and fistulae, condylomata (anal warts), pruritus ani, inflammatory bowel disease, and even neoplasia.⁶ A sudden onset of severe pain is more likely to point toward a fissure, an abscess, or a thrombosed hemorrhoid rather than a garden-variety internal hemorrhoid flare. If you have been attributing your symptoms to hemorrhoids for months without improvement, or if you notice bleeding that does not match your usual pattern, it is worth getting examined rather than self-treating indefinitely.

This is especially important when diarrhea itself is unexplained. Rectal bleeding during a known stomach bug is one thing. Rectal bleeding alongside persistent changes in bowel habits with no obvious cause warrants a conversation with a doctor to rule out something more serious.

Practical Steps to Reduce Flare-Ups During Diarrhea

Since diarrhea attacks hemorrhoids from several angles at once, the most effective response addresses multiple fronts. The first priority is always treating the diarrhea itself. If a medication is causing it, talk to your prescriber about alternatives. If an underlying condition like IBD or bile acid malabsorption is driving it, getting that condition managed cuts off the biggest source of repeated hemorrhoidal stress.

While the diarrhea is active, a few things help limit the hemorrhoid damage:

Minimize wiping friction: Use a bidet, a peri-bottle, or unscented wet wipes. Pat gently rather than rubbing. If the area is already raw, a thin layer of petroleum jelly or zinc oxide barrier cream can protect the skin between episodes.
Limit toilet-sitting time: Get up as soon as you are done. Sitting on the toilet longer than necessary increases pressure on the anal cushions, even if you are not actively straining.
Warm soaks: A shallow warm bath (a sitz bath) for ten to fifteen minutes after particularly rough episodes can relax the sphincter, improve blood flow, and ease pain. The thrombosed hemorrhoid study found that regular bathing was associated with lower risk, which aligns with this advice.³
Topical treatments: Over-the-counter creams, suppositories, and witch hazel pads can reduce swelling and itching during a flare. These do not fix the underlying problem, but they help you get through the acute phase with less misery.
Stay hydrated: Diarrhea pulls water and electrolytes out of your body. Dehydration makes stool consistency harder to stabilize once the diarrhea resolves, which can lead to a constipation rebound that prolongs the flare-up in a different way.

Fiber supplementation is frequently recommended for hemorrhoid management, though the evidence is less clear-cut than you might expect. Formal studies of medical therapies for hemorrhoids are limited, and fiber trials have produced inconsistent results.⁷ That said, fiber can help normalize stool consistency once acute diarrhea has passed, moving you away from both extremes. During active diarrhea, though, adding large amounts of insoluble fiber can sometimes make things worse, so timing matters.

Why Constipation Gets All the Attention

If you search for hemorrhoid causes, constipation dominates the results. There is a reason for that: straining against hard stool is the most intuitive and well-publicized cause. But the fixation on constipation has led many people to assume that keeping stool soft and loose is automatically protective, which is not the full story. Chronic loose stools carry their own risks, and in some populations the diarrhea-hemorrhoid link is just as strong as the constipation-hemorrhoid link.

The study that found strong associations between hemorrhoidal disease and multiple diarrheal disorders actually framed its findings as evidence of a potential pathogenic relationship, suggesting the medical community had underappreciated diarrhea as a driver of hemorrhoidal disease.⁴ The mechanisms are different from constipation, as outlined throughout this article, but the end result is the same: swollen, painful, bleeding hemorrhoidal tissue.

For people who alternate between constipation and diarrhea, as is common in certain types of IBS, the hemorrhoidal cushions essentially never get a break. They are squeezed and congested during constipation episodes, then chemically irritated and mechanically abraded during diarrhea episodes. This alternating pattern can be more damaging than either extreme alone, because the tissue never has a stable window in which to recover. If this describes your situation, getting a proper diagnosis for the bowel irregularity itself, rather than just treating the hemorrhoid symptoms, is likely to make the biggest long-term difference.

1
PubMed Central. Inflammatory bowel disease and risk for hemorrhoids: a Mendelian randomization analysis
2
PubMed Central. Bile acid diarrhoea: pathophysiology, diagnosis and management
3
PubMed Central. Aetiology of thrombosed external haemorrhoids: a questionnaire study
4
PubMed. Association of hemorrhoidal disease with diarrheal disorders: potential pathogenic relationship?
5
PubMed Central. Altered Gut Microbic Flora and Haemorrhoids: Could They Have a Possible Relationship?
6
Seminars in Colon and Rectal Surgery. Approaching the consult for “hemorrhoids”
7
PubMed Central. Rethinking What We Know About Hemorrhoids