Hemorrhoids form when the cushions of tissue lining your anal canal become swollen, stretched, or displaced from their normal position. These cushions exist in everyone and serve a purpose, but a combination of pressure, straining, and weakening support tissues causes them to enlarge and produce symptoms. About half of adults older than 50 have hemorrhoids, making this one of the most common conditions you’re unlikely to hear people talk about openly.
The Tissue That’s Already There
Most people think of hemorrhoids as something abnormal that suddenly appears, but the tissue involved is a normal part of your anatomy. Your anal canal contains three prominent cushions of blood vessels, connective tissue, and smooth muscle, positioned at roughly the 3, 7, and 11 o’clock positions when viewed from below. These cushions help with fine-tuned control of the anal sphincter and contribute to maintaining continence, particularly for gas and liquid stool.
At the level of a key anatomical landmark called the dentate line, these cushions are anchored to the underlying muscle by a suspensory ligament. That ligament acts like a tether, keeping the cushions in place during the everyday pressure changes of bowel movements. When this anchoring system weakens or the blood vessels inside the cushions become persistently engorged, the cushions swell, slide downward, or bulge outward. That’s when a normal structure becomes a problem.
How Pressure Causes the Damage
The central mechanism behind hemorrhoid formation is increased pressure in and around the anal canal. When you strain during a bowel movement, you raise the pressure inside your abdomen and pelvis, which in turn compresses the veins draining the anal cushions. Blood flowing into the cushions has difficulty flowing back out, so the vessels swell. A single episode of straining won’t typically cause trouble, but chronic or repeated straining stretches the vessels and, more importantly, gradually degrades the connective tissue holding the cushions in place.
Over time, the suspensory ligament loosens. The cushions begin to slide downward through the anal canal. This is the progression from occasional swelling to the kind of hemorrhoid that protrudes during a bowel movement or, eventually, stays protruded all the time. The damage is cumulative: each episode of excessive pressure weakens the support structures a little more, making the next episode more likely to cause symptoms.
Constipation, Low Fiber, and Straining
Constipation is the single most discussed driver of hemorrhoid formation, and the connection is straightforward. Low-fiber diets produce small, hard stools that are difficult to pass. Pushing harder and longer to evacuate them creates exactly the kind of sustained pressure that engorges the anal cushions and interferes with venous return. The recommended dietary fiber intake is about 14 grams per 1,000 calories consumed, which works out to roughly 28 grams per day on a standard 2,000-calorie diet. Most people fall well short of that number.
Fiber works by absorbing water and adding bulk to stool, making it softer and easier to pass with minimal effort. When your stool moves through the anal canal without requiring much force, the pressure on those vascular cushions stays low. This is why increasing fiber intake is consistently recommended both for preventing hemorrhoids and for managing mild ones that already exist.
Why Sitting on the Toilet Matters
Prolonged sitting on the toilet is an underappreciated contributor. The toilet seat’s shape leaves the anal area unsupported while gravity pulls blood downward into the pelvic veins. Spending extended time in that position, whether from constipation or from scrolling your phone, allows blood to pool in the anal cushions. If you’re also intermittently bearing down during that time, you’re combining the worst of both mechanisms: venous pooling and increased pressure. Keeping bathroom visits short and purposeful is one of the simplest changes that reduces hemorrhoid risk.
Pregnancy and Pelvic Pressure
Pregnancy creates a near-perfect environment for hemorrhoid formation through several overlapping factors. Rising progesterone levels relax the smooth muscle in the intestinal walls, slowing the contractions that move stool along. This hormonal shift makes constipation more likely, which means more straining. At the same time, as the fetus grows, it increases abdominal pressure and physically compresses the blood vessels in the pelvic floor. Blood returning from the rectal veins faces more resistance, so the anal cushions stay swollen for longer periods. The third trimester and labor itself, with its intense sustained pushing, carry the highest risk. Many pregnancy-related hemorrhoids resolve in the weeks after delivery as pelvic pressure returns to normal, though some persist.
How Aging Weakens the Support System
Age is a major factor, and it works independently from straining or diet. Over decades, the blood vessels and connective tissue near the anus naturally lose strength and elasticity. The suspensory ligament that anchors the cushions becomes less resilient. Softened, weakened tissues can’t handle the strain of hard pushing or long sitting the way they once could, so problems develop faster and from less provocation. This is why hemorrhoids are uncommon in young adults but affect roughly half of people by their fifties. The tissue simply becomes more vulnerable over time, and it takes less pressure to push a cushion out of position.
Internal vs. External Hemorrhoids
Where a hemorrhoid forms relative to the dentate line determines its type and what it feels like. Internal hemorrhoids develop above the dentate line, in tissue that has very few pain-sensing nerves. They tend to cause painless bleeding, often noticed as bright red blood on toilet paper or in the bowl. External hemorrhoids form below the dentate line, in skin that is richly supplied with pain nerves. These are the ones that hurt, especially if a blood clot forms inside them (a thrombosed hemorrhoid), creating a firm, tender lump near the anal opening.
Internal hemorrhoids are graded on a four-point scale based on how far they’ve slipped from their normal position. First-degree hemorrhoids swell into the anal canal during a bowel movement but don’t protrude outside. Second-degree hemorrhoids push out during straining but slide back in on their own once the effort stops. Third-degree hemorrhoids protrude and require you to push them back in manually. Fourth-degree hemorrhoids are permanently outside the anal canal and can’t be reduced. This grading reflects the progressive stretching and failure of the support ligament over time.
Other Contributing Factors
Heavy lifting raises intra-abdominal pressure in the same way straining on the toilet does. People who regularly lift heavy loads at work or in the gym create repeated spikes of downward force on the pelvic floor. Chronic diarrhea can also contribute, since frequent bowel movements irritate the anal canal and the repeated bearing down associated with urgency adds pressure. Obesity increases baseline abdominal pressure throughout the day, not just during bowel movements, keeping the venous system under constant low-grade strain. A sedentary lifestyle compounds the problem by reducing blood flow and allowing blood to pool in the pelvic region.
Genetics likely plays a role too. Some people inherit weaker connective tissue or vein walls, making them more susceptible to the same pressures that don’t bother others. If your parents dealt with hemorrhoids, your baseline risk is higher, though lifestyle factors still determine whether that predisposition actually produces symptoms.
What Keeps Them From Resolving
Once hemorrhoids have formed, the same factors that created them tend to perpetuate them. Swollen cushions are more easily irritated during subsequent bowel movements, which triggers more inflammation and swelling. The connective tissue, already stretched, doesn’t snap back to its original tightness the way elastic might after being overstretched for too long. This is why hemorrhoids tend to be a recurring issue rather than a one-time event. Breaking the cycle usually requires addressing the root causes: softening stools through fiber and hydration, reducing time on the toilet, and avoiding unnecessary straining. Without those changes, the structural damage continues to accumulate, and episodes become more frequent and more severe.