Hemorrhoids develop when the cushions of blood vessels and connective tissue inside your anal canal become swollen, stretched, or displaced. Everyone has these cushions; they’re a normal part of your anatomy that help with bowel control. Problems start when repeated pressure, weakened tissue, or both cause them to engorge with blood or slip out of position. Understanding the specific triggers helps explain why hemorrhoids are so common and what you can do to lower your risk.
What Hemorrhoids Actually Are
A common misconception is that hemorrhoids are varicose veins. They’re not. They’re clusters of blood vessels, smooth muscle, and connective tissue that sit just inside (or just outside) the anal canal. In their normal state, these cushions help seal the anus shut and cushion stool as it passes. You only notice them when something goes wrong: the blood vessels swell, the surrounding tissue stretches, and the cushion either bulges inward (internal) or outward (external).
The key to hemorrhoid formation is blood flow. When blood flowing into these cushions can’t drain back out efficiently, the tissue swells. Think of it like a balloon filling with water faster than it can empty. Over time, the connective tissue holding the cushion in place weakens, and the swollen cushion can start to prolapse, meaning it slips downward or protrudes outside the body.
Straining and Pressure: The Primary Trigger
The single most recognized trigger is straining during bowel movements. When you bear down hard, the pressure in your abdomen spikes and compresses the veins around your rectum, interfering with normal blood flow out of the hemorrhoidal cushions. Blood pools, the tissue engorges, and repeated episodes gradually stretch the connective tissue that holds everything in place.
Constipation is the classic setup for this kind of straining, but diarrhea can cause the same problem. Frequent, urgent bowel movements irritate and stress the same tissue. Any situation that forces you to push harder or sit longer on the toilet creates a similar effect. Prolonged toilet sitting, even without active straining, creates what’s been described as a tourniquet effect on the veins in the perianal area, trapping blood in the cushions. Most experts recommend keeping toilet sessions under 10 minutes to reduce this pressure.
The Role of Connective Tissue and Genetics
Diet and bathroom habits don’t explain everything. A large genetic study of nearly 950,000 people identified 102 regions of the genome associated with hemorrhoid risk. The genes involved primarily control smooth muscle function and the structural integrity of blood vessel walls and connective tissue in the gut. In other words, some people are born with tissue that’s more prone to stretching and weakening under pressure.
This aligns with an interesting finding from colonoscopy data: internal hemorrhoids don’t always correlate with constipation, low fiber intake, or irregular bowel habits. Instead, they correlate strongly with diverticulosis, another condition rooted in connective tissue changes. The researchers behind that finding suggest that structural vulnerability in the tissue itself may matter more than diet or stool consistency for many people, particularly when it comes to internal hemorrhoids. If your parents or siblings deal with hemorrhoids, your own risk is likely higher regardless of your habits.
Why Aging Makes It Worse
The connective tissue supporting your hemorrhoidal cushions weakens naturally with age. This degradation can begin as early as your 30s, which is why hemorrhoids become increasingly common from that decade onward. As the support structure loosens, it takes less pressure to cause a cushion to swell or prolapse. Activities that never caused problems in your 20s, like occasional constipation or a long road trip, can suddenly trigger symptoms.
Pregnancy and Hemorrhoids
Pregnancy creates a perfect storm of hemorrhoid triggers. The growing uterus puts direct physical pressure on the veins around the rectum, making it harder for blood to flow back toward the heart. At the same time, hormonal changes (particularly rising progesterone) slow digestion, leading to constipation. The combination of backed-up stool pressing on already compressed veins is why hemorrhoids are so common during the second and third trimesters, and especially during the pushing phase of labor.
Heavy Lifting and Physical Exertion
Lifting heavy weights, moving furniture, or any activity that makes you hold your breath and bear down creates the same kind of abdominal pressure spike as straining on the toilet. When you hold your breath under load, air gets forced downward against your internal organs, compressing the veins near your rectum. The mechanism is identical to what happens during a difficult bowel movement.
This doesn’t mean exercise causes hemorrhoids. The issue is technique. Breathing steadily through a lift keeps abdominal pressure more evenly distributed. Trying to lift more weight than your body can handle forces compensatory straining that puts your pelvic floor and rectal veins under unnecessary stress.
Other Contributing Factors
Several additional factors raise your risk or worsen existing hemorrhoids:
- Obesity: Excess body weight increases baseline pressure on the pelvic veins, similar to the effect of a pregnant uterus.
- Sedentary lifestyle: Sitting for long periods, whether at a desk or in a car, reduces blood flow from the lower body and can contribute to venous pooling in the rectal area.
- Low-fiber diet: While the direct link between fiber intake and internal hemorrhoids is weaker than once thought, low fiber still promotes hard, small stools that require more straining to pass. That straining remains a well-established trigger.
- Chronic cough or vomiting: Any condition that repeatedly spikes abdominal pressure can stress the hemorrhoidal cushions over time.
What Happens When Hemorrhoids Flare
Internal hemorrhoids typically cause painless bleeding, bright red blood on toilet paper or in the bowl. Because the tissue inside the anal canal has few pain-sensing nerves, you may not feel internal hemorrhoids at all unless they prolapse far enough to protrude outside. External hemorrhoids are a different experience. They sit under the sensitive skin around the anus, and when a blood clot forms inside one (thrombosis), the result is sudden, intense pain. This thrombosis is usually triggered by a specific event: heavy lifting, a bout of constipation, diarrhea, or even a dietary change. The pain comes from the clot rapidly stretching the nerve-rich skin surrounding it.
Most flare-ups resolve on their own within a week or two. Warm baths, over-the-counter creams, and softening your stool with fiber or fluids can speed relief. Thrombosed external hemorrhoids hurt the most in the first 48 to 72 hours, then gradually improve as the clot is reabsorbed.
How to Lower Your Risk
Since the core problem is pressure on weakening tissue, prevention centers on reducing that pressure. Eating enough fiber (25 to 30 grams per day) and drinking adequate water keeps stools soft and easy to pass, which cuts down on straining. Going to the bathroom when you first feel the urge, rather than waiting, helps avoid the harder stools that come with delay. Keeping toilet time under 10 minutes, and leaving your phone outside the bathroom, eliminates the passive sitting that traps blood in the cushions.
Regular physical activity improves circulation and helps prevent constipation. If you lift weights, focus on exhaling during the exertion phase rather than holding your breath. Maintaining a healthy body weight reduces chronic pressure on your pelvic veins. None of these steps can override a strong genetic predisposition entirely, but they address the modifiable factors that turn a vulnerability into a problem.