How Are Hemorrhoids Caused?

Hemorrhoids are caused by swelling and pressure in the veins around the anus and lower rectum. These veins are part of a normal cushion of tissue that helps keep the anal canal closed. When that tissue stretches or the veins inside it become engorged, the cushions enlarge and can bleed, itch, or bulge. The most common drivers are chronic straining during bowel movements, long stretches of sitting on the toilet, pregnancy, and ongoing constipation.

Nearly everyone has this tissue. The problem is not that it exists. The problem is what happens when pressure builds inside it repeatedly over time.

What Actually Happens Inside the Anal Veins

The anal canal is lined with a ring of spongy tissue called the hemorrhoidal cushions. These cushions contain blood vessels and connective tissue. They work like a soft seal, helping the anal canal stay closed at rest so stool and gas do not leak.

When you strain or sit for a long time, pressure rises inside those veins. The vessels stretch. The supporting connective tissue can loosen. Over months or years, that stretching becomes the enlarged tissue we call hemorrhoids.

Two locations matter here. Internal hemorrhoids sit above the dentate line, a boundary inside the anal canal. That area has no pain-sensing nerves, so internal hemorrhoids often bleed without hurting. External hemorrhoids sit below that line, where nerves are present. That is why external hemorrhoids tend to hurt or itch.

This distinction explains a pattern many people notice. Bright red blood on toilet paper with no pain usually points to an internal source. A tender lump near the opening usually points to an external one.

How Are Hemorrhoids Caused by Straining and Constipation?

Straining is the single most cited trigger. When you bear down, you raise pressure inside the abdomen and the veins below it. That pressure pushes blood into the anal cushions and stretches them.

Constipation sets up the conditions for straining. Hard stool takes more effort to pass. That effort is repeated pressure, and repeated pressure is what enlarges the tissue.

Two related habits make this worse:

• Sitting on the toilet for long periods, often while reading or scrolling on a phone
• Delaying a bowel movement when the urge comes, which allows stool to harden

The sitting part is easy to overlook. Gravity keeps blood pooled in the lower rectal veins while you sit. The longer you sit, the longer that pooling lasts. Even without hard stool, prolonged sitting alone can contribute.

This is where a common belief needs correcting. Hemorrhoids are not caused by “weak veins” in a general sense, and they are not a sign that something is fundamentally wrong with your circulation. They are a mechanical problem. Pressure plus time equals stretched tissue.

Why Does Pregnancy Cause Hemorrhoids?

Pregnancy raises the risk through several paths at once. A growing uterus presses on the veins that drain the lower body. Hormonal changes relax the walls of blood vessels. Constipation becomes more common. And the pushing stage of labor adds a sharp burst of pressure.

These factors combine, which is why hemorrhoids are common during pregnancy and in the weeks after delivery. For many women, symptoms improve once the pressure from the uterus eases and hormone levels return to baseline.

No clinical guidelines exist for treating hemorrhoids specifically in pregnant women with a single standard approach. Treatment decisions in pregnancy should go through a clinician, since some over-the-counter products are not recommended during pregnancy.

What Other Factors Raise Your Risk?

Several conditions and habits increase the odds of developing hemorrhoids or making existing ones worse.

Chronic diarrhea can irritate the anal tissue and increase the frequency of bowel movements, which adds repeated pressure.

Low fiber intake contributes to hard stool and constipation, which feeds back into straining.

Obesity raises pressure inside the abdomen, similar to the effect of pregnancy.

Prolonged sitting, whether at a desk or on the toilet, keeps pressure on the lower rectal veins.

Lifting heavy objects repeatedly can raise intra-abdominal pressure the same way straining does.

Aging plays a role because the connective tissue that supports the anal cushions weakens over time. This is part of why hemorrhoids become more common with age.

One factor that gets blamed unfairly is spicy food. Spicy food does not cause hemorrhoids. It can make existing ones feel worse during a bowel movement, but it does not create the underlying tissue changes.

What Symptoms Point to Hemorrhoids?

Symptoms depend on where the hemorrhoid is and whether it has thrombosed, meaning a blood clot has formed inside it.

Internal hemorrhoids commonly cause:

• Bright red blood on toilet paper or in the bowl
• A feeling of incomplete emptying after a bowel movement
• Painless bleeding, in many cases

External hemorrhoids commonly cause:

• Itching or irritation around the anus
• Pain or discomfort, especially when sitting
• A hard, tender lump if a clot forms

A thrombosed external hemorrhoid is the painful one. The pain tends to peak in the first day or two and then gradually improves as the body reabsorbs the clot.

Bleeding deserves attention regardless of the cause. Rectal bleeding can come from hemorrhoids, but it can also come from other conditions, including colorectal cancer. Any new rectal bleeding should be evaluated by a clinician rather than assumed to be hemorrhoids. This is one of the few places where the stakes are high enough that self-diagnosis is a bad idea.

Does Sitting on Cold Surfaces Cause Hemorrhoids?

No. Sitting on a cold floor, a concrete step, or a cold bench does not cause hemorrhoids. This is a long-standing folk belief with no supporting evidence.

Temperature does not drive the pressure changes inside the anal veins. What matters is mechanical pressure and time, not surface temperature.

The belief likely persists because cold surfaces are uncomfortable, and people associate discomfort with harm. The actual risk comes from prolonged sitting on any surface, cold or warm.

Can Hemorrhoids Be Prevented?

Prevention focuses on reducing pressure and softening stool. These steps are widely recommended because they address the mechanical causes directly.

• Get enough fiber. Fiber softens stool and reduces straining. Dietary fiber goals vary by age and sex, and official recommendations are available from federal dietary guidelines.
• Drink enough water. Fluid helps fiber do its job.
• Do not delay the urge to go. Waiting lets stool harden.
• Limit time on the toilet. Aim to finish rather than linger.
• Stay physically active. Movement supports regular bowel function.
• Avoid straining. If nothing is happening, get up and try later.

These measures reduce the pressure that causes hemorrhoids to enlarge. They are not a guarantee, because age and genetics also play a role. But they address the factors you can actually control.

When Should You See a Doctor?

See a clinician if you have rectal bleeding for the first time, if bleeding is heavy or persistent, or if you have pain that does not improve. Also seek care if you notice a change in bowel habits that lasts more than a few weeks, or if you have unexplained weight loss alongside rectal symptoms.

Most hemorrhoids are not dangerous. But the symptoms overlap with conditions that are, which is why evaluation matters. A clinician can usually tell the difference with a physical exam and, when needed, a scope.

Treatment ranges from at-home measures like fiber and sitz baths to office procedures and, in some cases, surgery. Which option fits depends on the type, severity, and your overall health. That is a conversation to have with a clinician rather than a decision to make from a search result.