Hemorrhoids come from increased pressure on the veins in and around the anus, causing them to swell, stretch, and sometimes bulge. About half of all adults develop hemorrhoids by age 50, making them one of the most common digestive complaints. The underlying cause is almost always some form of sustained or repeated pressure that interferes with normal blood flow in the rectal area.
How Hemorrhoids Actually Form
Your anal canal naturally contains cushions of blood vessel-rich tissue. These cushions aren’t a defect. They account for roughly 15 to 20 percent of the resting pressure that keeps your anus closed, and they help you distinguish between solid stool, liquid, and gas. Hemorrhoids develop when pressure builds in the area and blood has trouble draining back out of these cushions. The veins engorge, the tissue swells, and over time the cushions can stretch, bleed, or push outward.
Think of it like a one-way traffic jam. Blood flows into these vascular cushions easily, but anything that compresses or blocks the outflow causes a backup. That backup is what makes the tissue balloon and become symptomatic.
Straining and Low-Fiber Diets
The single most common trigger is straining during bowel movements, and the most common reason people strain is a low-fiber diet. Without enough fiber, stools become small and hard. Pushing them out forces you to bear down repeatedly, which engorges the hemorrhoidal cushions by interfering with venous return. Over months or years, that repeated pressure stretches the tissue until it stays swollen or starts to bleed.
Fiber softens stool and adds bulk, which means it passes more easily. The National Institute of Diabetes and Digestive and Kidney Diseases recommends increasing fiber intake both to treat existing hemorrhoids and to prevent new ones. Fruits, vegetables, whole grains, and legumes are the most practical sources. If your diet is currently low in fiber, increasing it gradually (rather than all at once) helps avoid gas and bloating.
Sitting Too Long on the Toilet
Spending extended time on the toilet, whether you’re scrolling your phone or reading, creates what specialists describe as a tourniquet effect. The seated position on a toilet opening allows gravity to pool blood in the perianal veins while reducing the body’s ability to drain it back. Even without active straining, this prolonged sitting engorges the hemorrhoidal cushions. Keeping bathroom visits brief, ideally under five minutes, reduces this pressure significantly.
Pregnancy and Hormonal Changes
Pregnancy is one of the strongest risk factors, and it works through two mechanisms at once. First, the growing uterus physically presses on the pelvic veins, increasing blood flow to the area while making it harder for blood to drain from the rectal veins. Second, rising progesterone levels relax the walls of veins throughout the body, allowing them to swell more easily under that increased pressure. The combination means hemorrhoids frequently appear in the second and third trimesters, and the straining of labor itself can worsen them further.
Many pregnancy-related hemorrhoids improve within weeks after delivery once the uterine pressure is gone and hormone levels normalize. But for some people, the tissue has stretched enough that symptoms linger.
Heavy Lifting and Physical Strain
Any activity that sharply raises pressure inside your abdomen can push blood into the rectal veins. Weightlifting is a well-known example: holding your breath while hoisting a heavy load forces air downward into the lungs and compresses the organs below, swelling the veins near the rectum. The mechanism is essentially the same as straining on the toilet.
This doesn’t apply only to gym settings. Moving furniture, carrying heavy boxes, or any repetitive lifting with breath-holding creates the same abdominal pressure spike. Exhaling during the exertion phase of a lift, rather than holding your breath, helps prevent that internal compression.
Other Contributing Factors
Chronic constipation and chronic diarrhea both contribute, though for different reasons. Constipation causes repeated straining. Diarrhea irritates and inflames the anal lining, and frequent bowel movements mean more time bearing down. People with either condition are at higher risk than those with regular, soft stools.
Age plays a role as well. The connective tissue supporting the hemorrhoidal cushions weakens over time, making it easier for them to slide downward and protrude. Obesity increases baseline abdominal pressure in a similar way to pregnancy, and people who sit for long periods at work may experience reduced blood flow from the pelvic area throughout the day.
Internal vs. External Hemorrhoids
Where the swelling occurs determines the type. Internal hemorrhoids form inside the rectum, above a boundary called the dentate line. This area has few pain-sensing nerves, so internal hemorrhoids are usually painless. The most common sign is bright red blood on toilet paper or in the bowl. You typically can’t see or feel them unless they’ve prolapsed, meaning they’ve pushed far enough to bulge outside the anus.
External hemorrhoids develop under the skin around the anal opening, in tissue dense with nerve endings. These are the ones that hurt. They often cause itching, irritation, swelling you can feel, and sharp pain, especially if a blood clot forms inside the swollen vein (a condition called a thrombosed hemorrhoid). That clot creates a firm, tender lump that can be intensely painful for several days before the body gradually reabsorbs it.
Many people have both types simultaneously, particularly if the underlying cause (chronic straining, low fiber, prolonged sitting) has been present for a long time. The good news is that the same lifestyle changes, more fiber, shorter bathroom visits, staying hydrated, and avoiding unnecessary straining, address the root pressure problem regardless of which type you’re dealing with.