Causes and Risks Factors of Hemorrhoids

How Pregnancy, Obesity, and Diet Can Increase Risk

woman using the toilet at home
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Hemorrhoids, commonly referred to as piles, can be caused by straining during a bowel movement or by conditions such as pregnancy or obesity which place undue pressure on the lower abdomen. By doing so, the veins in and around the anus can begin to stretch and swell abnormally, causing pain, burning, and itchiness.

As frustrating as hemorrhoids can be, even scientists are not entirely sure why some people develop them and others do not.

What we do know is that there are certain factors that can increase a person's risk. Some of these are modifiable (meaning there are things we can do to change them) and others are non-modifiable (such as a person's genetics or age).

Common Causes

Hemorrhoids will affect three of every four people at one time or another in their lives. While adults between 45 and 65 are at greatest risk, they can affect people who are far younger, often without explanation.

Hemorrhoids are most commonly associated with bowel movement problems, including:

  • Chronic constipation or diarrhea
  • Straining during bowel movements
  • Sitting for a long time on the toilet

Any of these conditions can affect the blood vessels located in the so-called hemorrhoid cushion. This is an internal structure o the anal canal composed of connective tissues, smooth muscles, and blood vessels known as sinusoids.

Straining of any sort can cause the sudden rise in blood pressure in the hemorrhoid cushion.

This, in turn, can cause a vessel to slip from the muscles and ligaments meant to hold it in place. The same can occur if you have an enormous sneeze.

Chronic diarrhea or constipation can make things worse by triggering persistent inflammation of the anal and rectal (anorectal) tissues. Sitting on the toilet only exacerbates the problem by stretching the walls of blood vessels so thinly that they begin to bulge and dilate.

Lifestyle Factors

While bowel movement problems are the most common causes of hemorrhoids, there are certain lifestyle factors that can increase a person's risk both directly and indirectly.

Low-Fiber Diet

Dietary fiber is essential to digestive health, and many people simply don't get enough. Low-fiber diets (with less than 25 to 30 grams of fiber per day) can significantly increase your risk of constipation. The same applies if you are dehydrated and drink less than eight glasses of water per day (or roughly a half gallon).

According to guidance from the National Institute of Diabetes and Digestive and Kidney Disorders (NKNKD), diets rich in the following foods can significantly increase your risk of constipation:

  • Cheese
  • Chips
  • Fast food
  • Ice cream
  • Prepared foods, including frozen meals and snack foods
  • Processed foods
  • Red meat

By contrast, the increased intake of insoluble fiber may help restore normal bowel function.


Hemorrhoids are common in overweight and obese people for several reasons. In addition to eating the wrong foods and not drinking enough fluids, the excessive abdomen girth and weight places stress on the muscles of the pelvic floor and, in turn, the hemorrhoid cushion.

Physical inactivity and the absence of regular exercise only adds to the burden, causing a general loss of muscle tone (including the anorectal muscles) while affecting gastrointestinal motility (often resulting in alternating bouts of diarrhea and constipation)

Hemorrhoids and Pregnancy

Hemorrhoids are also a common occurrence during pregnancy. While the pressure exerted by the weight of the baby can contribute to their development, hormonal changes can also cause blood vessels to swell excessively.

During the pregnancy itself, the increased size of the uterus can exert pressure on the inferior vena cava, a large vessel on the right side of the body that receives blood from the lower limbs. Doing so impedes the flow of blood back to the heart and causes any vessels below the uterus to dilate, including those of the hemorrhoid cushion.

Childbirth can place further strain by the sheer force of the labor contractions, leading to the development of hemorrhoids after delivery.

It is estimated that as many as 35 percent of women will develop hemorrhoids during the course of her pregnancy. The risk typically increases with each subsequent birth.

Genetics Risks

Genetics can also play a role in the development of hemorrhoids. One such example is an inherited disorder called Ehlers-Danlos syndrome (EDS) in which the lack of collagen can lead to the impairment of pelvic floor tissues. Hemorrhoids are a common symptom of EDS and can sometimes foreshadow a more serious complication known as rectal prolapse in which the bowel falls partially or completely out of the body.

Another commonly noted defect is the absence of valves within hemorrhoidal veins which can lead to excessive vascular pressure and swelling.

Medical Causes

Hemorrhoids are a common feature in many health conditions, some serious and others not-so-serious. These include:

  • Anal fissures (tears) or fistulas (infection of the anal canal)
  • Anal injury, such as from anal sex
  • Ascites (the accumulation of fluid in the abdominal cavity, often seen in advanced liver disease)
  • Inflammatory bowel diseases (IBD), such as Crohn's disease and ulcerative colitis
  • Intra-abdominal abscesses
  • Rectal prolapse

Because many of these conditions are serious and/or treatable, it is important not to ignore any hemorrhoid that is either worsening or failing to improve.

While hemorrhoids can sometimes bleed, you should see a doctor if the bleeding is persistent and is accompanied by abdominal pain, changes in bowel habits, bloody stools, and unexplained weight loss. This may be a sign of colon or rectal cancer, both of which require immediate attention.

The same goes for chronic diarrhea and constipation. Neither should be considered normal, and steps should be taken to identify any underlying cause (such a lactose or gluten intolerance) that might explain or contribute to the condition.


Sun, Z. and Migaly, J. "Review of Hemorrhoid Disease: Presentation and Management." Clin Colon Rectal Surg. 2016; 29(1):22-29. DOI: 10.1055/s-0035-1568144.

National Institute of Diabetes and Digestive and Kidney Disorders (NDDKD). "Eating, Diet, & Nutrition for Hemorrhoids: What should I eat if I have hemorrhoids?" Bethesda, Maryland; October 2016.