What Causes Hemorrhoids to Flare Up: Main Triggers

Hemorrhoid flare-ups are driven by anything that increases pressure on the veins in and around the anal canal or weakens the tissue supporting them. The most common triggers are straining during bowel movements, sitting on the toilet too long, eating too little fiber, not drinking enough water, and, for many people, alcohol. But the full picture includes some surprises, including a popular belief about spicy food that the evidence doesn’t clearly support, and a structural vulnerability in your connective tissue that you may have inherited.

What Happens During a Flare-Up

Everyone has anal cushions, which are pads of tissue rich in blood vessels that sit just inside the anal canal. They help with continence and are a normal part of your anatomy. Hemorrhoids become a problem when those cushions swell, shift out of position, or both. The underlying issue involves the blood vessels in those cushions dilating abnormally, while the connective tissue that anchors them in place weakens and stretches.

A flare-up occurs when something pushes this process past your body’s ability to compensate. The veins engorge with blood that isn’t draining efficiently, the tissue swells, and you get the classic symptoms: pain, itching, bleeding during bowel movements, or tissue that protrudes from the anus. Understanding the triggers means understanding what increases that vascular pressure or accelerates the breakdown of the supporting tissue.

Straining and Time on the Toilet

Straining to pass a bowel movement is the single most intuitive trigger, and the evidence backs it up. When you bear down, you spike pressure inside the abdomen and directly onto the veins of the anal canal. Constipation is one of the strongest predictors of a hemorrhoidal crisis, with one study of patients presenting to a specialized clinic finding constipation carried nearly four times the odds of triggering a flare compared to patients without it.¹

What fewer people realize is that simply sitting on the toilet for a long time, even without straining, is a major problem. The shape of a toilet seat leaves the anal canal unsupported while gravity pulls blood downward into the hemorrhoidal veins. A cross-sectional study comparing patients with anorectal diseases to controls found that toilet sessions lasting more than 20 minutes were dramatically more common in patients: about 8% of the patient group sat that long, compared to just 0.5% of healthy controls.² Clinical guidelines now recommend keeping toilet time to three to five minutes. If you’re scrolling your phone on the toilet, you’re almost certainly exceeding that. This is one of the easiest triggers to eliminate.

Low Fiber Intake and Dehydration

If straining is the immediate mechanical trigger, a low-fiber diet is what sets the stage. Fiber softens and bulks the stool, which means it passes with less effort. Without enough fiber, stools become hard and compact, requiring more force and more time to pass. A case-control study found that people eating less than 12 grams of fiber per day had roughly seven times the odds of developing internal hemorrhoidal disease compared to those with higher intake.³ For context, most nutrition guidelines recommend 25 to 30 grams daily, meaning many people are well short of what their bowels need.

Dehydration compounds the problem. Water works with fiber to keep stool soft. In that same study, drinking less than two liters of water per day was associated with nearly nine times the odds of internal hemorrhoidal disease, an even stronger link than low fiber alone.³ The two factors reinforce each other: fiber without water can actually make constipation worse, because dry fiber just creates a bulkier, harder stool.

Evidence-based guidelines rate dietary modification, specifically increasing fiber and fluid intake, as one of the strongest conservative recommendations for managing hemorrhoidal disease.⁴ The effect is meaningful enough that for many people with mild to moderate hemorrhoids, this single change can reduce or eliminate flare-ups without any other intervention.

Alcohol and Spicy Food

Alcohol is a well-documented trigger for hemorrhoidal crises. A French study of patients seen in specialized consultation found that recent alcohol intake roughly doubled the odds of a flare-up.¹ Alcohol has several ways to make hemorrhoids worse: it’s a vasodilator, which means it widens blood vessels and can increase engorgement; it contributes to dehydration, which hardens stools; and heavy consumption can cause diarrhea, which irritates the anal lining and involves its own form of straining.

Spicy food, on the other hand, sits in a more confusing place in the evidence. Many people with hemorrhoids are told to avoid it, and that same French study did find a strong association between spicy diet and hemorrhoidal crisis, with about five times the odds compared to people who hadn’t recently eaten spicy food.¹ But a separate case-control study found that patients with internal hemorrhoidal disease actually consumed pepper and chili powder less frequently than healthy controls.³

How do you reconcile these? It’s possible that spicy food irritates existing hemorrhoids and triggers flare-ups in people who already have the condition, without actually causing hemorrhoids in the first place. It’s also possible that patients who already have hemorrhoids learn to avoid spicy food, skewing the case-control data. Either way, the blanket advice to “stop eating spicy food” is more complicated than it sounds. If you notice a personal pattern where a spicy meal leads to a flare within a day or two, it’s reasonable to cut back, but the evidence doesn’t support spicy food as a universal trigger the way constipation and low fiber clearly are.

Physical Exertion and Heavy Lifting

Intense physical activity, especially heavy lifting, can trigger a flare-up through a mechanism similar to straining on the toilet. When you hold your breath and push against a heavy load (a technique called the Valsalva maneuver), intra-abdominal pressure spikes, and that pressure transmits directly to the hemorrhoidal veins. The French consultation study found that recent unusual physical activity carried about 2.8 times the odds of a hemorrhoidal crisis.¹

This creates a tricky situation because moderate physical activity is actually protective against hemorrhoids in the long run. Regular exercise improves bowel motility, reduces constipation, and helps maintain a healthy weight, all of which lower hemorrhoid risk.⁵ The key distinction is between moderate, regular activity and sudden, intense bouts of heavy lifting or straining. If you have active hemorrhoids, you don’t need to stop exercising. You may want to temporarily avoid exercises that require heavy abdominal bracing, and focus on activities like walking, swimming, or lighter resistance training until the flare settles.

Pregnancy

Pregnancy is one of the strongest predictors of hemorrhoidal flare-ups, and it stacks multiple triggers at once. The growing uterus presses on the pelvic veins and inferior vena cava, which impedes the return of blood from the lower body and increases pressure in the hemorrhoidal veins. Hormonal changes relax the walls of blood vessels and soften connective tissue. Constipation becomes more common, partly due to hormonal shifts and partly because of iron supplementation. And labor itself involves sustained, intense bearing-down that can push hemorrhoids into full-blown prolapse.

The good news is that pregnancy-related hemorrhoids are among the most treatable, in part because many resolve or improve after delivery once the mechanical pressure is removed. A comparative study of pregnant women with hemorrhoids found that simple sitz baths (sitting in warm water for short periods) achieved complete healing in all patients tested, compared to about 85% of those treated with anorectal cream.⁶ Warm water soaking is safe, free, and effective enough to be a first-line approach during pregnancy.

Stress and the Gut-Brain Axis

Stress doesn’t directly swell a hemorrhoidal vein, but it can set off a chain of events that ends in a flare-up. When you’re under chronic stress, your body activates the autonomic nervous system and the hormonal stress response, both of which alter gut function.⁷ For some people, stress causes constipation. For others, it triggers diarrhea. Either extreme is bad for hemorrhoids: constipation leads to straining, and frequent loose stools irritate the anal lining and cause repeated wiping, which worsens external hemorrhoids.

Stress can also change your behavior in ways that feed into other triggers. People under stress tend to eat worse, drink less water, consume more alcohol, sit more, and rush through meals. They may also tense their pelvic floor muscles without realizing it, which can interfere with smooth bowel movements. So while stress isn’t a direct mechanical cause, it’s a multiplier that makes everything else on this list more likely.

Obesity and Prolonged Sitting

Carrying excess weight increases chronic pressure on the pelvic floor and the veins of the lower rectum, which is why obesity is consistently identified as a contributing factor for hemorrhoidal disease.⁵ The effect is similar to what happens during pregnancy, except instead of a growing uterus, it’s abdominal fat creating sustained downward pressure on the hemorrhoidal vessels.

Prolonged sitting outside the bathroom matters too, though less dramatically than sitting on the toilet. People who sit for long stretches during the workday have reduced venous return from the lower body, meaning blood pools in the pelvic region. Combined with the typical dietary patterns of sedentary office workers, this creates favorable conditions for flare-ups. Standing desks, walking breaks, and periodic movement through the day aren’t just ergonomic advice for your back; they also help your hemorrhoids.

Why Some People Are More Prone Than Others

Two people can share identical diets, exercise habits, and toilet routines, and one will have recurring hemorrhoid flare-ups while the other never does. Part of the explanation lies in the connective tissue that holds the anal cushions in place. Research comparing tissue samples from hemorrhoid patients to healthy controls has found a measurably different balance of collagen types. Specifically, patients with hemorrhoidal disease had a significantly lower ratio of type I collagen (the stiffer, structural kind) to type III collagen (the more flexible, stretchier kind).⁸ A separate study confirmed this, finding that type I collagen levels in hemorrhoid patients were roughly half those of controls.⁹

In practical terms, this means the scaffolding holding the anal cushions in place is weaker and stretchier in some people, making their cushions more likely to slide, swell, and prolapse under the same pressures that someone else’s tissue can handle without trouble. This isn’t something you can fix with diet or behavior. It’s a structural vulnerability, likely genetic, that explains why hemorrhoids tend to run in families and why some individuals keep having flare-ups despite doing everything “right.” Understanding this can be reassuring if you’ve been frustrated by recurring symptoms even after improving your diet and habits: it’s not that you’re failing at prevention; you’re working with tissue that has a lower threshold for damage.

The Portal Hypertension Myth

If you or someone you know has liver disease, you may have been told that the liver condition causes hemorrhoids. This belief was widespread in medicine for decades, based on the reasoning that elevated pressure in the portal vein system would back up into the rectal veins and cause them to swell. It sounds logical, but it’s wrong.

A prospective study of over 100 patients with liver cirrhosis found no significant difference in the prevalence of hemorrhoids between cirrhotic patients and healthy controls matched for age and sex. Both groups had hemorrhoids at roughly the same rate, around 80%.¹⁰ Cirrhotic patients did have a much higher rate of anorectal varices, which are dilated veins that develop in the rectal wall due to portal hypertension, but these are a separate condition from hemorrhoids. The hemorrhoidal veins and the variceal veins are distinct structures, and the degree of portal pressure in cirrhotic patients had no relationship to whether they had hemorrhoids.¹¹

This distinction matters because the treatments are completely different. Anorectal varices in someone with portal hypertension require management of the underlying liver disease and can bleed dangerously. Hemorrhoids in the same patient are managed the same way as in anyone else: fiber, fluids, topical treatments, and, if needed, procedural intervention. Conflating the two can lead to unnecessary alarm or inappropriate treatment.

Age and the Weakening of Supportive Tissue

Hemorrhoids become more common with age, peaking roughly between the ages of 45 and 65. One reason is cumulative wear on the connective tissue anchoring the anal cushions. The collagen changes described earlier can worsen over time as part of the body’s general loss of structural tissue integrity with aging. The vascular cushions that were once firmly tethered begin to slide more easily, which is why prolapse (hemorrhoids that protrude from the anus) becomes more common in older adults.

Interestingly, though, the French consultation study found that being under 50 was independently associated with hemorrhoidal crises, with about twice the odds of presenting with an acute flare compared to older patients.¹ This may seem contradictory, but the explanation likely lies in the difference between having hemorrhoids and having acute flare-ups. Younger people may have more volatile triggers: heavier alcohol intake, more intense physical activity, more erratic diets, and perhaps more psychological stress. Older adults may have more chronic, low-grade disease but fewer dramatic crises. If you’re in your 30s or 40s and dealing with recurrent flare-ups, you’re not unusual.

Smoking

Smoking is listed among the behavioral risk factors for hemorrhoidal disease, likely because of its effects on vascular health and tissue repair.⁵ Nicotine constricts blood vessels and impairs circulation, which can interfere with the normal drainage of the hemorrhoidal venous plexus. Smoking also slows wound healing, meaning that minor tissue damage from a bowel movement takes longer to repair, and the cycle of injury and incomplete recovery can sustain a flare. Smoking also tends to come packaged with other risk factors, including poorer diet, higher alcohol use, and more sedentary behavior, making it hard to isolate its independent contribution. Still, if you’re looking for one more reason to quit, your hemorrhoids will thank you.

Occupational Risk

Having any occupational activity, as opposed to being unemployed or retired, was associated with about 40% higher odds of hemorrhoidal symptoms in the French study.¹ The association likely reflects the constraints that work imposes on your daily routine. People with demanding jobs may delay going to the bathroom when they feel the urge, eat irregularly, sit or stand for long unbroken stretches, and experience chronic stress, all of which feed into the triggers described above. Jobs that involve heavy manual lifting add the direct mechanical component as well. You can’t always change your occupation, but you can modify how you handle breaks, hydration, and meals during the workday.

1
Gastroentérologie Clinique et Biologique. Risk factors associated with hemorrhoidal symptoms in specialized consultation
2
Frontiers in Surgery. Toilet behaviors and lifestyle factors in anorectal diseases: a cross-sectional analysis
3
La Tunisie Médicale. Dietary habits associated with internal hemorrhoidal disease: a case-control study
4
Frontiers in Surgery. Lifestyle and Risk Factors in Hemorrhoidal Disease
5
Journal of Education, Health and Sport. Hemorrhoidal Disease – The Role of Dietary, Behavioral and Lifestyle Factors in Prevention and Conservative Management
6
PubMed. Hemorrhoids during pregnancy: Sitz bath vs. ano-rectal cream: A comparative prospective study of two conservative treatment protocols
7
PubMed Central. Hemorrhoidal disease and its genetic association with depression, bipolar disorder, anxiety disorders, and schizophrenia: a bidirectional mendelian randomization study
8
PubMed Central. Abnormalities in collagen composition may contribute to the pathogenesis of hemorrhoids: morphometric analysis
9
Journal of Translational Science. Decreased collagen ratio type I/III in association with hemorrhoidal disease
10
Journal of Hepatology. Relationship of portal pressure, anorectal varices and hemorrhoids in cirrhotic patients
11
PubMed. Anorectal varices, haemorrhoids, and portal hypertension