Hemorrhoids develop when the cushions of vascular tissue in your anal canal become swollen, stretched, or inflamed. About one in four adults has hemorrhoids at any given time, according to a global meta-analysis, and the condition becomes more common with age. Understanding what drives that swelling helps explain why hemorrhoids are so widespread and what you can do to lower your risk.
How Hemorrhoids Actually Form
The first thing to know is that everyone has hemorrhoidal tissue. These are clusters of blood vessels, smooth muscle, and connective tissue that line the anal canal. They serve a real purpose: they account for roughly 15 to 20 percent of resting anal pressure and help you distinguish between solid stool, liquid, and gas. Hemorrhoids are not a disease you “catch.” They become a problem when that normal tissue swells beyond its usual size.
When pressure inside or around the rectum increases, the network of small arteries and veins in these cushions dilates and engorges. Over time, the connective tissue and muscle fibers anchoring those cushions to the rectal wall stretch out and weaken. The swollen tissue can then slide downward and bulge into or out of the anal canal, a process called prolapse. Because these cushions have a rich blood supply with direct connections between arteries and veins, any trauma to the engorged surface tends to produce bright red bleeding.
Straining and Constipation
The single most common trigger is straining during bowel movements. When you bear down hard to pass stool, you dramatically increase pressure in the veins of your lower rectum. Do this repeatedly over weeks or months, and those veins stay swollen. Chronic constipation is the classic setup: hard, dry stools require more force to pass, and the longer stool sits in the colon, the more water your body absorbs from it, making the next attempt even harder. It’s a cycle that feeds itself.
Diarrhea can cause the same problem from the opposite direction. Frequent, urgent bowel movements irritate the anal canal and keep the tissue inflamed, so chronic digestive conditions that swing between constipation and loose stools are a double risk.
Low Fiber Intake
Diet plays a direct role because it determines how easy your stools are to pass. Fiber absorbs water and adds bulk, producing softer stools that move through the colon without requiring much effort. Most Americans get roughly half the fiber they need. The general recommendation is 25 to 30 grams per day from food sources like vegetables, fruits, whole grains, and legumes. Falling well short of that target over time makes constipation, and therefore hemorrhoids, far more likely.
Prolonged Sitting on the Toilet
Spending a long time on the toilet, even without actively straining, contributes to hemorrhoid development. The shape of a toilet seat concentrates pressure on the rectum and anus in a way that ordinary chairs do not. When you sit there for 10 or 15 minutes scrolling your phone, blood pools in the anal cushions and the surrounding veins stay compressed. Making bathroom trips brief and purposeful is one of the simplest preventive steps you can take.
Pregnancy
Hemorrhoids are extremely common during pregnancy, especially in the third trimester, for several overlapping reasons. As the uterus grows, it presses directly on the veins that drain the pelvis and rectum, slowing blood return and causing those vessels to swell. Blood volume also increases substantially during pregnancy, forcing veins throughout the body to handle more blood than usual. On top of that, hormonal shifts slow digestion, leading to constipation. The combination of extra blood, extra pressure, and harder stools makes hemorrhoid flare-ups almost inevitable for many pregnant people, particularly during labor and delivery when straining peaks.
Heavy Lifting and Physical Strain
Any activity that raises pressure inside your abdomen can push blood into the rectal veins and keep it there. Heavy weightlifting is the most obvious example, particularly when done with a breath-holding technique (the Valsalva maneuver) or without engaging the core properly. But the same mechanism applies to jobs that involve frequent lifting, moving heavy furniture, or any sustained physical exertion where you’re bearing down. The pressure spike itself isn’t always the problem. It’s the repeated spikes, day after day, that gradually stretch the vascular cushions past the point where they spring back to normal.
Aging and Tissue Breakdown
Hemorrhoid prevalence rises steadily with age, and the reason is structural. The connective tissue anchoring the anal cushions degrades over time. Elastin, the protein that gives tissue its snap-back quality, breaks down gradually as you get older. The collagen fibers that hold the vascular cushions in place also lose tensile strength and become more disorganized. Together, these changes mean the tissue that’s supposed to keep everything anchored loosens its grip. Blood pools more easily, veins dilate, and the cushions eventually slide downward. This is why someone in their 50s or 60s can develop hemorrhoids without any obvious change in diet or habits. The tissue simply can’t withstand the same pressures it handled decades earlier.
For comparison, the point prevalence in children is roughly half that of adults (around 13.5 percent versus 25 percent), largely because their connective tissue is still intact and resilient.
Obesity and Sedentary Habits
Carrying excess body weight increases baseline pressure on the pelvic floor and the veins that run through it. This is the same mechanism at work during pregnancy, just without a defined endpoint. A sedentary lifestyle compounds the issue: sitting for hours reduces blood circulation in the lower body and allows blood to pool in the rectal veins. Regular movement helps keep blood flowing and reduces the time those veins spend under sustained pressure.
Multiple Causes Usually Overlap
Hemorrhoids rarely result from a single factor. A typical scenario involves someone who eats a low-fiber diet, sits at a desk most of the day, spends extra time on the toilet, and is now in their 40s with connective tissue that’s less forgiving than it used to be. Each factor adds incremental pressure or reduces the tissue’s ability to handle it. That’s also why prevention works best as a combination of changes rather than a single fix: more fiber, more water, shorter bathroom visits, regular physical activity, and attention to lifting technique all chip away at the pressure load on your rectal veins simultaneously.