Hemorrhoids develop when the cushions of tissue lining your anal canal become swollen, stretched, or displaced from their normal position. About 1 in 4 adults worldwide have them at any given time, and the number climbs higher with age. Understanding how they form starts with knowing what’s already there: hemorrhoidal tissue isn’t something that appears out of nowhere. It’s a normal part of your anatomy that becomes a problem when specific pressures and changes push it past its limits.
Hemorrhoids Are Normal Tissue Gone Wrong
Everyone has hemorrhoidal tissue. These cushions are a complex weave of blood vessels, muscle fibers, and connective tissue that line the inside of the anal canal. They serve an important purpose: they act as a soft, expandable seal that helps maintain continence, contributing roughly 15 to 20% of the resting pressure that keeps the anal canal closed. Think of them as gaskets that fine-tune the seal.
Problems start when the connective tissue holding these cushions in place breaks down. Microscopic studies of hemorrhoid tissue removed during surgery consistently show the same thing: the supportive framework of connective tissue is loose, fragmented, and degraded. Without that scaffolding, the cushions slide downward, blood pools inside them, and they swell. That’s the shift from normal anatomy to the condition people recognize as hemorrhoids.
The Role of Pressure and Straining
The single biggest mechanical trigger is increased pressure in the abdomen and pelvis pushing down on the veins in the anal canal. Because rectal veins lack valves (unlike veins in your legs), blood can’t be efficiently routed back up toward the heart when pressure builds. During straining on the toilet, for example, blood flow backs up into the hemorrhoidal cushions, causing them to engorge and stretch. Over time, repeated episodes weaken the vessel walls and the connective tissue around them, making the cushions permanently enlarged or prone to sliding out of place.
This is why constipation is so closely linked to hemorrhoids. Low-fiber diets produce small, hard stools that require more effort to pass. That effort translates directly into the kind of sustained downward pressure that overwhelms the venous drainage system in the anal canal. But constipation isn’t the only culprit. Chronic diarrhea can be just as damaging through a different path: frequent loose stools increase pressure in the anal area, irritate the lining, and lead to repeated wiping that inflames the surrounding skin. People who alternate between constipation and diarrhea face a compounding effect, with the back-and-forth stressing the rectal tissue from both directions.
Why Sitting on the Toilet Matters
Spending extended time on the toilet creates what researchers describe as a tourniquet effect. The seated position on a toilet opening allows the pelvic floor to relax and the hemorrhoidal tissue to drop slightly into the bowl. The longer you sit, the more blood pools in those cushions with limited venous return. A study of smartphone use and toilet habits found that 37% of people who brought their phones to the bathroom spent more than 5 minutes per trip, compared to just 7% of those who didn’t. That extra time adds up.
“The longer you’ve been sitting in that position, the more your connective tissue around those hemorrhoidal cushions weakens,” as one gastroenterologist explained to MedPage Today. The takeaway is straightforward: if you’re done, get up. Scrolling through your phone on the toilet is one of the most avoidable risk factors for hemorrhoid development.
How Aging Weakens the Support System
As you get older, the muscle fibers that help anchor hemorrhoidal cushions gradually get replaced by connective tissue. This shift means the cushions lose their structural support and become more likely to slide, sag, or prolapse. It’s a slow process, which is why hemorrhoids become more common in middle age and beyond, though younger adults can develop them too if other risk factors are present.
A large genetic study identified 102 regions of the genome linked to hemorrhoid risk. The genes involved primarily affect smooth muscle function and the integrity of blood vessel and gut tissue. In other words, some people are born with connective tissue and vascular walls that are more vulnerable to the pressures described above. Family history is a recognized risk factor, and this research helps explain why: the tendency toward weaker structural tissue in the anal canal can be inherited.
Pregnancy and Hormonal Changes
Pregnancy creates a perfect storm for hemorrhoid development. The growing baby presses directly on the large blood vessels in the pelvis, physically altering blood flow and making it harder for blood to return from the lower body. At the same time, hormonal changes relax the walls of blood vessels throughout the body, slowing venous return and making smaller veins in the pelvis and legs more likely to swell. Add in the constipation that many pregnant people experience, and the combination of mechanical pressure, hormonal effects, and straining makes hemorrhoids extremely common during the second and third trimesters.
The strain of labor itself, particularly prolonged pushing, can also cause hemorrhoids to develop or worsen suddenly. Most pregnancy-related hemorrhoids improve after delivery as the pressure resolves, though they don’t always disappear entirely.
Heavy Lifting and Physical Strain
Weightlifters and people in physically demanding jobs face a less obvious risk. When you hold your breath while lifting something heavy, you perform what’s called a Valsalva maneuver: air is forced down into the lungs while the abdominal muscles contract, dramatically increasing pressure on internal organs. That pressure transmits directly to the veins near the rectum, causing them to swell. The mechanism is essentially the same as straining during a difficult bowel movement, just triggered by a barbell instead of constipation.
This doesn’t mean you need to avoid exercise. Exhaling during the exertion phase of a lift, rather than holding your breath, significantly reduces the pressure spike. Regular physical activity actually helps prevent hemorrhoids by promoting healthy bowel function, so the goal is technique, not avoidance.
How Fiber Helps Prevent the Problem
Increasing fiber intake is the most consistently supported preventive measure. Fiber softens and adds bulk to stool, which reduces the need to strain during bowel movements. Clinical trials have tested various forms of supplemental fiber for hemorrhoid management, with dosages typically ranging from 7 to 20 grams per day of sources like psyllium, bran, or plantain-based fiber. These studies show meaningful reductions in symptoms including bleeding and discomfort.
For context, most adults in Western countries eat around 15 grams of fiber daily, well below the recommended 25 to 30 grams. Closing that gap through whole grains, fruits, vegetables, and legumes, or through a fiber supplement, directly addresses the low-residue diet that researchers consistently identify as a primary driver of hemorrhoid development. Drinking enough water alongside increased fiber is important, since fiber without adequate fluid can actually worsen constipation.
Other Contributing Factors
Obesity increases baseline abdominal pressure, putting constant low-level stress on pelvic veins. Diabetes and hypertension also show associations with hemorrhoid risk in population studies, likely through their effects on blood vessel health. Chronic coughing, whether from smoking, lung disease, or allergies, repeatedly spikes abdominal pressure in the same way that straining on the toilet does.
Sedentary lifestyles contribute as well. Prolonged sitting in general, not just on the toilet, can impair blood flow in the pelvic region. People who sit for long stretches at work may benefit from standing breaks, both for hemorrhoid prevention and overall vascular health.