What the sources say causes hemorrhoids

These are published descriptions of why hemorrhoid veins swell. ahem has not examined anyone and does not sell a treatment.

Mayo Clinic dates its symptoms page August 23, 2025. On the copy opened October 26, 2026, it calls hemorrhoids swollen veins in the anus and lower rectum, like varicose veins. It says the veins around the anus tend to stretch under pressure and may bulge or swell. Hemorrhoids can develop from increased pressure in the lower rectum.

Cleveland Clinic updated its hemorrhoid page on May 5, 2025. Opened the same day as the Mayo Clinic page, it says too much pressure on the veins in the anus or rectum, along with irregular bowel movements, leads to the swelling. NIDDK last reviewed its symptoms page in October 2016. Opened October 26, 2026, it prints a cause list and does not add a separate sentence about vein walls.

On the symptoms page checked October 26, 2026, NIDDK says the causes of hemorrhoids include:

• Straining during bowel movements.
• Sitting on the toilet for long periods of time.
• Chronic constipation or diarrhea.
• A low-fiber diet.
• Weakening of the supporting tissues in the anus and rectum that happens with aging.
• Pregnancy.
• Often lifting heavy objects.

NIDDK keeps pregnancy as its own line. Aging is the line about supporting tissues. The low-fiber item is why the diet page exists. The gram figure and a few foods from NIDDK's table are on fiber, fluids, and hemorrhoid symptoms.

Mayo Clinic's cause list, on the page checked October 26, 2026, shares straining, long sitting (especially on the toilet), long-lasting diarrhea or constipation, a low-fiber diet, pregnancy, and regularly lifting heavy items. It adds two items NIDDK's cause list does not print: being obese, and anal intercourse.

Aging sits in Mayo Clinic's risk-factor section on that page. The tissues that support the veins in the rectum and anus can weaken and stretch as people age, and the risk of hemorrhoids rises with that. The same section says pregnancy can do this because the baby's weight puts pressure on the anal area. Pregnancy is also on the cause list above. The page gives both sentences.

Mayo Clinic's overview says internal hemorrhoids develop inside the rectum and external hemorrhoids develop under the skin around the anus. Which symptoms each type is described as having is part of how long hemorrhoid symptoms usually last. The cause list does not assign a person to one type.

Cleveland Clinic's pressure list, checked October 26, 2026, includes pushing hard to pass stool, straining to lift heavy objects or weightlifting, sitting on the toilet for long periods, chronic constipation or diarrhea, a low-fiber diet, pregnancy, overweight or obesity, and anal intercourse. Obesity and anal intercourse line up with Mayo Clinic. The page's cause bullets do not repeat NIDDK's separate line about aging tissues.

MedlinePlus hosts a hemorrhoid overview that credits NIDDK. Opened October 26, 2026, its cause list follows NIDDK's items, with one wording difference: weakening of the supporting tissues can happen with aging and pregnancy, in a single bullet. NIDDK lists pregnancy on its own line. MedlinePlus does not print a review date of its own on that page. The page reads as NIDDK's overview in another layout. Mayo Clinic and Cleveland Clinic are the other institutions quoted above.