Hemorrhoids form when the blood vessels in and around your anus swell under repeated or sustained pressure. The tissues that normally support these vessels stretch out, the vessel walls thin, and they begin to bulge. If the pressure continues, they can protrude further and bleed. About half of adults experience noticeable hemorrhoid symptoms at some point, and the supportive tissue in the anal canal can start weakening as early as your 30s.
The Physical Process Behind Hemorrhoids
Your anal canal contains cushions of blood vessels that help with bowel control. Under normal conditions, these cushions stay in place thanks to a network of supportive tissue. When pressure in the lower rectum increases, whether from straining, sitting, or other causes, the vessels inside those cushions engorge with blood. The surrounding tissue stretches to accommodate the swelling, and over time it loses its ability to snap back. The vessel walls thin out, making them prone to bleeding, and the swollen tissue can eventually push out through the anal opening.
This is the same basic mechanism whether the hemorrhoid forms inside the rectum or on the outer rim of the anus. Internal hemorrhoids develop higher up in the anal canal, in tissue that doesn’t have pain-sensing nerves, which is why they often show up as painless bleeding. External hemorrhoids form under the skin around the anus, where nerve endings are dense, so they tend to hurt, especially if a blood clot forms inside them.
Straining and Constipation
The single most common trigger is straining during a bowel movement. When stool is hard or difficult to pass, you bear down, which spikes pressure inside your abdomen and forces blood into the rectal veins. Do this often enough, whether from chronic constipation or simply rushing through a bowel movement, and those vessels start to stretch permanently. A low-fiber diet is usually at the root of the problem: without enough bulk, stool becomes compact and harder to move.
The recommended daily fiber intake is about 14 grams for every 1,000 calories you eat, which works out to roughly 28 grams on a standard 2,000-calorie diet. Most people fall well short of that number, and the gap shows up as harder stools and more straining over the years.
Sitting on the Toilet Too Long
Sitting on a toilet creates a specific kind of pressure problem. The shape of the seat leaves the anal area unsupported while gravity pulls blood downward into the rectal veins. The longer you sit, the more blood pools there, creating a tourniquet-like effect that engorges the vessels. Scrolling through your phone for 20 minutes might feel harmless, but it’s one of the more reliable ways to develop hemorrhoids over time.
There’s no hard clinical cutoff, but most specialists recommend keeping toilet sessions under 10 minutes. If nothing is happening, get up and try again later. Leaving your phone outside the bathroom is the simplest fix most people overlook.
Chronic Diarrhea
Constipation gets most of the attention, but frequent loose stools cause hemorrhoids through a different path. Chronic diarrhea means repeated trips to the bathroom, each one involving pressure on the anal blood vessels and wiping that irritates the surrounding skin. The constant irritation inflames the tissue and makes the vessels more vulnerable to swelling. People who cycle between diarrhea and constipation, common with irritable bowel syndrome, put their rectal tissue through alternating types of stress, which compounds the damage.
Heavy Lifting
Lifting heavy objects, whether at a gym or on a job site, mimics the same pressure pattern as straining on the toilet. People naturally hold their breath and bear down when handling heavy weight, which forces air into the lungs while compressing the abdominal organs. That spike in abdominal pressure pushes directly on the rectal veins. Weightlifters who regularly attempt loads near their limit are particularly susceptible, because the heavier the weight, the harder the strain and the more pressure transmitted to the pelvic floor.
Exhaling during the exertion phase of a lift, rather than holding your breath, reduces how much pressure reaches the rectal area. It won’t eliminate the risk entirely, but it lowers the cumulative stress on those vessels.
Pregnancy
Pregnancy creates a perfect storm for hemorrhoid development. As the uterus grows, it presses on the veins that drain the rectal area, making it harder for blood to flow back toward the heart. Blood pools and the vessels swell. On top of that, blood volume increases significantly during pregnancy to support the fetus, which means the veins throughout the body are handling more fluid than usual. The extra volume puts additional outward pressure on vessel walls that are already under strain.
Hormonal changes also loosen connective tissue throughout the body, including the tissue holding rectal vessels in place. Add in the constipation that many pregnant women experience, and the third trimester becomes the peak window for hemorrhoid symptoms. Most pregnancy-related hemorrhoids improve after delivery once the extra pressure resolves.
Aging and Tissue Weakening
Age works against you in a structural way. The muscle and connective tissue in the anal canal gradually lose strength over the decades. Research on aging anal tissue shows that muscle content drops significantly with age, replaced by stiffer collagen and fibrous tissue. In animal studies, muscle made up about 70% of the anal canal tissue in young subjects but only 52% in older ones. That loss of muscle means less support holding the vascular cushions in place, so even moderate pressure from normal bowel movements can cause bulging that wouldn’t have been a problem at 25.
This is why hemorrhoids become more common with each decade of life, even in people who haven’t changed their diet or habits. The threshold for developing them simply gets lower as the tissue degrades.
Obesity and Prolonged Sitting
Carrying extra body weight increases baseline pressure on the pelvic floor at all times, not just during bowel movements. The rectal veins bear some of that load constantly, which accelerates the stretching process. Obesity also correlates with lower fiber intake and more sedentary behavior, both of which independently raise the risk.
Prolonged sitting outside the bathroom matters too, though less than toilet sitting specifically. People with desk jobs or long commutes keep sustained pressure on the pelvic region for hours. Regular movement breaks help blood circulate out of the rectal veins rather than pooling there.
Reducing Your Risk
Most hemorrhoid prevention comes down to reducing how much pressure your rectal veins experience day to day. Eating enough fiber (aiming for that 28-gram daily target through vegetables, fruits, legumes, and whole grains) keeps stools soft so they pass without straining. Drinking adequate water works alongside fiber; one without the other is less effective.
Beyond diet, the behavioral changes are straightforward: limit toilet time to 10 minutes, avoid straining or forcing a bowel movement, breathe through exertion when lifting, and break up long periods of sitting. None of these eliminate the possibility entirely, especially as you age and the supporting tissue naturally weakens, but they remove the most controllable sources of repeated pressure on the anal canal.