Exactly what causes hemroids is unknown, but we do know that they are caused by increased pressure in the veins of the anus. The upright posture of humans alone forces a great deal of pressure on the rectal veins of the anus, which sometimes causes them to bulge.
Sitting in one place to often
Straining while moving bowels (from constipation or hard stools). This is the most common cause.
Excessive rubbing, or cleaning around the anus
Diarrhea
Sitting on the toilet too long
Severe coughing
Childbirth
Lifting heavy objects
Anal infection
Other contributing factors include:
Aging
Chronic diarrhea or constipation
Pregnancy
Misfortune of Heredity
Frequent use of laxatives or enemas resulting in faulty bowel function
Straining during bowel movements
Too much reading on the toilet
The bottom line is the tissues supporting the veins are stretched. As a result, the veins dilate; and the vein walls become thin and bleed. If the pressure continues to stretch the veins, they become weakened and protrude out of the anus. Hemroids are very common, especially during pregnancy and after childbirth.