The most common causes of hemorrhoids are straining during a bowel movement, severe constipation, and acute or chronic diarrhea, reports Healthline. Other common causes include sitting on the toilet for prolonged periods, obesity, pregnancy, low-fiber diet, rectal surgery and spinal cord injury, says MedicineNet.com.
One reason for straining while having bowel movements is a low-fiber diet, which may also force an individual to sit for prolonged periods on the toilet to empty the bowels. Straining during bowel movements hampers blood flow in and out of the anus. This causes blood to pool and blood vessels to enlarge in that region leading to swelling and increase in the pressure in these blood vessels, reports Healthline. It is these swollen veins that develop due to increased pressure in the lower rectum that are called as hemorrhoids, states Mayo Clinic.
Increased pressure in the lower rectum can also occur due to severe constipation and diarrhea. Similarly, pregnant women may suffer from hemorrhoids because their expanding uterus puts pressure on the veins in this area, says Healthline. Additionally, hormonal changes that occur in pregnant women might weaken their rectal and anal muscles leading to hemorrhoids, explains MedicineNet.com.
Other causes of hemorrhoids include obesity, spinal cord injury, previous rectal surgery and colon cancer, which all increase pressure in the anal region, states MedicineNet.com.