Hemorrhoids develop when the cushions of blood vessels and connective tissue inside your anal canal swell, stretch, or slide out of place. Everyone has these cushions from birth. They only become a problem when repeated pressure causes them to engorge with blood or when the tissue anchoring them weakens over time. About 11% of adults have symptomatic hemorrhoids at any given time, and the peak age range is 41 to 60.
What Hemorrhoids Actually Are
Hemorrhoids aren’t varicose veins, despite the common comparison. They’re clusters of blood vessels, smooth muscle, and connective tissue that line the anal canal. These clusters form cushions that help with continence, and they’re held in place by a connective tissue ligament attached to the underlying muscle. When that support system breaks down or the blood vessels inside the cushions swell from excess pressure, the cushions bulge, bleed, or protrude.
Internal hemorrhoids form above a boundary inside the anal canal called the dentate line. They drain into veins that flow toward the liver. External hemorrhoids sit just below that line, under the skin around the anus. They can form anywhere around the circumference of the opening, and they sometimes develop a blood clot inside them (thrombosis), which creates a hard, painful lump.
Straining During Bowel Movements
The single most common trigger is straining to pass stool. When you hold your breath and bear down, you dramatically increase the pressure inside your lower abdomen. That force pushes directly against the veins in the rectum, causing the hemorrhoidal cushions to engorge and stretch. Do this repeatedly over weeks or months, and the connective tissue anchoring those cushions begins to degrade.
Chronic constipation is the classic setup. Hard, dry stools require more effort to pass, which means more straining and more pressure on the same vulnerable tissue. But chronic diarrhea is nearly as problematic. Frequent loose stools irritate the anal canal and keep you on the toilet longer, creating a similar cycle of pressure and inflammation.
Low Fiber Intake
Fiber is what keeps stool soft and bulky enough to pass without effort. Federal dietary guidelines recommend 14 grams of fiber per 1,000 calories you eat, which works out to about 28 grams a day on a standard 2,000-calorie diet. Most people fall well short of that. Without enough fiber from fruits, vegetables, whole grains, or legumes, stool becomes compact and harder to move, setting up the straining pattern that feeds hemorrhoid development.
Sitting on the Toilet Too Long
The shape of a toilet seat is uniquely bad for your hemorrhoidal tissue. When you sit on one, the opening allows the tissue around your anus to hang unsupported while gravity and your body weight push blood into the vessels below. A few minutes is fine. But scrolling your phone for 15 or 20 minutes keeps that pressure applied continuously. The general advice is to get up after 10 minutes. If nothing is happening, leave and come back later. Keeping your phone out of the bathroom removes the main reason people linger.
Heavy Lifting and Physical Exertion
Lifting heavy objects, especially while holding your breath, spikes the pressure inside your abdomen in the same way straining on the toilet does. The force transmits directly to the veins around the anus. This is why hemorrhoids are common among weightlifters and people whose jobs involve repeated heavy lifting. The risk increases with poor technique: if you’re bracing with your core and breathing out during exertion, the pressure spike is smaller. If you’re holding your breath and clenching, it’s much larger.
Pregnancy
Pregnancy creates a perfect combination of hemorrhoid triggers. As the uterus grows, it presses on the veins in the pelvic area and partially blocks the return flow of blood from the lower body. Blood pools in the rectal veins, causing them to swell. At the same time, rising progesterone levels relax the walls of your veins, making them more likely to stretch and bulge under that pooled blood. The increased blood volume of pregnancy adds further pressure to the system. Many women develop hemorrhoids during the third trimester or during the pushing phase of labor, when abdominal pressure peaks.
Aging and Tissue Breakdown
The tissues supporting the veins in your rectum and anus weaken and stretch as you get older. This is a gradual process. The connective tissue ligament that holds internal hemorrhoids in place loses its structural integrity, and the cushions begin to slide downward under forces that wouldn’t have bothered them a decade earlier. This is why hemorrhoids become more common with age, even in people who haven’t changed their diet or habits. The cushions that stayed put at 30 may start to prolapse at 55 simply because the scaffolding around them has degraded.
Genetics Play a Role
A large genetic study from Karolinska Institutet identified 102 regions of the human genome that increase the risk of hemorrhoidal disease. When researchers examined individual hemorrhoidal cells, they found the relevant genes were primarily active in blood vessels and smooth muscle of the gastrointestinal tract. The conclusion: severe hemorrhoid disease is at least partly caused by an inherited dysfunction in intestinal muscle and connective tissue. If your parents dealt with hemorrhoids, your baseline tissue quality may make you more susceptible, even before lifestyle factors come into play. The researchers confirmed this using genetic risk scores across more than 180,000 people in Scandinavian and German biobanks, finding a direct correlation between genetic risk and disease severity.
Obesity and Prolonged Sitting
Carrying excess weight increases the chronic pressure on your pelvic floor. Surveys show that people with hemorrhoidal disease are slightly more likely to be obese than the general population (21% vs. 19%). Sitting for long periods at a desk or in a car also keeps steady pressure on the rectal area, though this is a weaker risk factor than straining or low fiber intake. The combination of a sedentary job, a low-fiber diet, and excess body weight creates compounding pressure that the anal cushions absorb day after day.
How Multiple Causes Stack Up
Most hemorrhoids don’t come from a single cause. They develop when several of these factors overlap. A person with a genetic predisposition who eats a low-fiber diet, sits for long stretches at work, and spends extra time on the toilet is loading pressure onto tissue that’s already structurally vulnerable. Pregnancy adds a temporary but intense version of the same pattern. Understanding which factors apply to you is the most useful part of this picture, because the modifiable ones (fiber intake, toilet time, lifting technique, hydration) are where prevention actually works.