What causes hemorrhoids

Hemorrhoids start as normal tissue. The anal canal has cushions of blood vessels and supporting tissue. When those cushions enlarge or slip downward, they become what people call hemorrhoids. A plain overview of what hemorrhoids are is the companion to this page. This one stays on the pressure that pushes the cushions out of place, and on how strong the evidence is for each cause.

The NIDDK list of hemorrhoid causes names straining during bowel movements, sitting on the toilet for a long time, chronic constipation or diarrhea, a low-fiber diet, weakening of the supporting tissues with aging, pregnancy, and often lifting heavy objects ¹. Those items show up in clinic after clinic. They are not equally proven.

Some of the best studies were set up to test that list, and they split. Constipation shows up in one large colonoscopy study and looks unrelated in a genetic study. Body weight looks harmful in one data set and neutral in another. Pregnancy is common in the third trimester and, in a different study, leaves no trace years later. The sections below keep those disagreements in the open.

What pressure does to the anal cushions

In 1975, Thomson described specialized cushions of tissue lining the anal canal and argued that piles are those cushions after they have slipped down ². A 2012 review uses almost the same definition: hemorrhoids are the symptomatic enlargement and downward displacement of the normal anal cushions. The review also describes wear in the supporting connective tissue, and changes in the blood vessels inside the cushion ³.

The cause of that slip is still partly guesswork. A 2019 review by Sandler and Peery calls the cause speculative. Low fiber and constipation have been the leading explanation since the 1970s, and that review says they have not been proven ⁴. In the United States they are the third most common outpatient gastrointestinal diagnosis, with nearly 4 million office and emergency visits a year ⁴.

The practical picture is pressure from the abdomen, repeated often enough to stretch the supports. Straining is the pressure you can feel.

Straining, and the position you sit in

Straining is the cause NIDDK puts first ¹. How you sit changes how hard you have to push. In a small study of 28 healthy volunteers, both the time needed to feel empty and the effort of straining dropped sharply in a squat compared with sitting on a standard toilet or a lower one ⁸. A later study of a footstool in healthy adults found less straining (odds ratio 0.23, 95% CI 0.18 to 0.30) and a better sense of emptiness (odds ratio 3.64) ⁹. Bowel movements also took longer without the footstool.

These are studies of straining, not of who later develops hemorrhoids. They still match the mechanism: less force on the cushions, less often. Feet up, knees above hips, and no hovering. The step-by-step version is on toilet habits that help hemorrhoids.

Constipation: the studies do not agree

Constipation is the cause most people expect. One study supports it. Two lines of evidence push back.

Peery and colleagues looked at 2,813 adults who had a colonoscopy in a colorectal adenoma prevention trial, and who had detailed records of bowel habits, diet, and activity. Hemorrhoids were taken from the colonoscopy reports. Of the group, 1,074 had hemorrhoids recorded. Constipation was linked to a higher prevalence (odds ratio 1.43, 95% CI 1.11 to 1.86) ⁵. That is the cleanest “yes” in the modern colonoscopy data.

Johanson and Sonnenberg, in 1990, compared the epidemiology of hemorrhoids with the epidemiology of constipation across U.S. and British data sets. About 10 million people in the United States reported hemorrhoids, a prevalence of 4.4%. Reports peaked from age 45 to 65 and fell after 65. Hemorrhoids before age 20 were unusual. Constipation did the opposite: it climbed after age 65 and was more common in groups where hemorrhoid reports were less common. The authors wrote that those patterns call a simple causal link into question ⁶. A summary of that 1990 study is the short version.

A 2024 Mendelian randomization study, which uses inherited gene variants as a stand-in for a habit, asked whether constipation and diarrhea actually cause hemorrhoids. Genetically predicted constipation did not (odds ratio 0.97, 95% CI 0.91 to 1.03). Diarrhea did not either (odds ratio 1.00, 95% CI 0.99 to 1.01). More frequent stools did (odds ratio 1.28, 95% CI 1.05 to 1.55). The authors also reported a reverse analysis that linked constipation and hemorrhoids (odds ratio 1.21, 95% CI 1.13 to 1.28) ⁷. Put the two directions side by side and constipation is not a settled cause. The paper itself says the clearer signals were frequent bowel movements and waist-to-hip ratio, not constipation or diarrhea.

If your stools are hard, treat that on its own merits. The food side is on the hemorrhoid diet. A single spicy meal is a different question, checked in does spicy food cause hemorrhoids.

Diarrhea

Chronic diarrhea sits next to constipation on the NIDDK list ¹. Loose, frequent stools mean more wiping and more time on the toilet. The genetic study did not find that diarrhea causes hemorrhoids (odds ratio 1.00) ⁷. Diarrhea stays on the clinical list as a flare trigger, with little support from that genetic study as a root cause.

Long sits on the toilet

NIDDK lists sitting on the toilet for long periods ¹. Two studies looked at the habit directly, and they do not match in strength.

In 2025, Ramprasad and colleagues surveyed 125 adults at a screening colonoscopy and had two endoscopists look for hemorrhoids. Forty-three percent had hemorrhoids. Sixty-six percent used a smartphone on the toilet. Among phone users, 37.3% spent more than five minutes per visit, compared with 7.1% of people who did not use a phone. After adjustment for age, sex, body mass index, exercise, straining, and fiber, phone use on the toilet was tied to a 46% higher risk (p = 0.044) ¹⁰. The study is small and cross-sectional: it cannot prove the phone came before the hemorrhoids. The full PLOS One paper is worth reading if you want the limits. We walk through them on does scrolling on the toilet cause hemorrhoids.

An earlier survey of 500 Israeli adults found toilet reading in 52.7%. Readers stayed longer. They reported hemorrhoids slightly more often (23.6% versus 18.2%), and that gap was not statistically significant. The authors called the habit common and benign ¹¹. Longer sits show up in both studies. A clear rise in hemorrhoids shows up in one.

A low fiber diet

Low fiber is on the NIDDK cause list ¹. In Peery’s colonoscopy study, people with the highest grain-fiber intake had lower odds of hemorrhoids than people with the lowest (odds ratio 0.78, 95% CI 0.62 to 0.98). The finding was for grain fiber specifically, not for every fiber type they checked ⁵. Sandler and Peery’s later review still treats a low-fiber diet as unproven as the historical root cause ⁴.

What is not in dispute is that most people eat less fiber than the guidelines suggest. A summary of U.S. intake data says only about 5% of the population meets recommendations ¹⁵. The NIDDK page on eating for hemorrhoids uses the Dietary Guidelines figure of 14 grams of fiber per 1,000 calories, or 28 grams on a 2,000-calorie day ¹⁴. Add it slowly so bloating does not make you strain in a new way.

If the plate is not getting you there, a psyllium powder is a simple next step. Our notes on products are on the best fiber supplements for hemorrhoids. You can add up a normal day first with the fiber calculator.

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Fiber as a treatment for bleeding, which is a different question from fiber as a cause, is covered with the trial numbers on bleeding hemorrhoids.

Pregnancy

Pregnancy is the cause with the clearest timing. Poskus and colleagues followed 280 pregnant women through delivery and one month after. Perianal disease developed in 43.9%. Of those cases, 1.6% appeared in the first trimester, 61% in the third trimester, 34.1% after delivery, and 3.3% at one month. Hemorrhoids were diagnosed in 114 women, 40.7% of the whole group ¹². Constipation during pregnancy was a strong predictor (odds ratio 18.98, 95% CI 7.13 to 50.54). Straining in labor for more than 20 minutes and a baby heavier than 3800 grams were predictors too, with very wide confidence intervals, so the size of those risks is uncertain ¹².

That is pressure during a pregnancy, measured while it is happening. Peery’s colonoscopy study asked a different question: among women already at the age of screening, did a past pregnancy show up as more hemorrhoids? Comparing women who had been pregnant with women who had not, the odds ratio was 0.93 (95% CI 0.62 to 1.40), which is no clear link ⁵.

Safe relief for this season is on hemorrhoids during pregnancy. Trouble that starts with a long second stage of labor is on postpartum hemorrhoids.

Aging

NIDDK lists weakening of the supporting tissues in the anus and rectum with aging, and says people older than 50 are more likely to have hemorrhoids ¹. Johanson’s survey curve is more specific: reports rise through midlife, peak from 45 to 65, and decline after 65 ⁶. The tissue-wear story from Lohsiriwat fits the rise ³. The drop after 65 is a reminder that “older” is not a straight line, and that survey reports are not the same thing as cushions seen on a scope.

Heavy lifting

Often lifting heavy objects is on the NIDDK cause list ¹. The idea is the same abdominal pressure that straining produces, repeated at the gym or at work. Peery’s study measured physical activity and did not find a clear link with hemorrhoids (odds ratio 0.83, 95% CI 0.66 to 1.03) ⁵. That activity measure is not hours of heavy lifting. The colonoscopy and genetic studies cited here did not measure lifting, so this cause rests on the clinical list and on the straining mechanism.

During a flare, the useful change is to stop breath-holding and to ease the loads that make you strain. Exercise with hemorrhoids goes through what to keep and what to pause.

One related Peery result is easy to misread. Sedentary behavior was linked to lower odds of hemorrhoids (odds ratio 0.80, 95% CI 0.65 to 0.98), and physical activity was not clearly protective ⁵. That finding argues against “sitting all day at a desk causes hemorrhoids.” It does not argue against walking, and it does not excuse long sits on the toilet. Those are different kinds of sitting.

Body weight

Here the data sets disagree in public, which is useful.

Riss and colleagues examined 976 adults in an Austrian screening program. Hemorrhoids were present in 38.93%. In the multivariate analysis, each one-point increase in body mass index raised the risk of hemorrhoids by 3.5% ¹³.

Peery’s larger colonoscopy study did not find that. Overweight was odds ratio 0.89 (95% CI 0.72 to 1.09). Obesity was odds ratio 0.86 (95% CI 0.70 to 1.06). Neither was significant ⁵. The open version of that study is the place to see how they defined the groups.

Yu’s genetic study found a causal link with waist-to-hip ratio adjusted for body mass index (odds ratio 1.11, 95% CI 1.06 to 1.64) ⁷. When the authors tested several positive findings together, waist-to-hip ratio was no longer significant (p = 0.74), while more frequent stools still were. A higher waist measurement is a plausible pressure story. It is not a result that survived every way of analyzing the same genetic data.

Taken together: one screening study says higher body mass index matters, one colonoscopy study says overweight and obesity do not, and one genetic study says waist-to-hip ratio might, until other factors are included. Extra weight is a reasonable thing to work on if it comes with constipation or straining. It is not, by itself, a proven cause.

What is still worth changing

You do not need a perfect cause to pick a useful habit. The steps that lower straining are the ones the cause list and the mechanism point to, even where the risk-factor studies disagree ^1,4.

1. Soften the stool with food fiber, aiming near 14 grams per 1,000 calories, and add water so the fiber does not sit dry in the gut ¹⁴.
2. Use a footstool if sitting on the toilet makes you push ^8,9.
3. Get up when the bowel movement is done. Keep the phone outside the bathroom ¹⁰.
4. During pregnancy, treat constipation early. The third trimester is when new hemorrhoids clustered in the Poskus cohort ¹².
5. During a flare, skip breath-holding lifts ¹.

The daily version of that list is on how to prevent hemorrhoids.

A cause you can name, such as a week of constipation or a long toilet sit, does not prove the blood is from a hemorrhoid. If one of those warning signs is present, get it checked before you spend months adjusting fiber.