Classified as either internal or external, hemorrhoids are a condition in which the veins located in the rectum and anus become swollen and enlarged. Some hemorrhoids can be treated minimally, but when hemorrhoids start to bleed, far more serious problems can arise. Bleeding hemorrhoids occur when the hemorrhoids become scratched, usually through passage of hard stools. This can lead to complications.
Pain while sitting or while having bowel movements is a common complication with bleeding hemorrhoids, states MedlinePlus. This usually happens when an internal hemorrhoid prolapses and becomes gripped by the external anal sphincter during defecation. When this happens, congestion occurs and blood flow is impeded in the concerned area, causing strangulation. This occurrence causes considerable pain, often known in layman's terms as an "acute attack of piles." Reduction or complete removal of hemorrhoids through a hemorrhoidectomy is required at this point. Another cause of pain is fibrosis, in which the tissues of the anal opening lose their elasticity. Though it is uncommon, suppuration, or the formation of pus when the bleeding hemorrhoid becomes infected, can also cause considerable pain.
MedlinePlus notes that severe bleeding of hemorrhoids could lead to iron-deficiency anemia, a condition in which there is a decrease in the body's number of red blood cells because of too little iron. This usually happens when there is a prolonged loss of blood, although significant blood loss in bleeding hemorrhoids is very uncommon.
The blood in a hemorrhoid's swollen veins can form blood clots, which can then be transported to other parts of the body and cause thrombosis, explains MedlinePlus. A thrombosis can be dangerous since it can lodge in the extremities and cause pain and lack of circulation. It becomes even far more dangerous when the blood clot is transported to the brain, causing stroke and eventually, death. Hemorrhoids with clots usually need surgical intervention so as to avoid possible fatal complications of thrombosis.
According to MayoClinic.com, hemorrhoids can restrict blood flow to the surrounding tissues, thus depriving those tissues of much-needed oxygen. The blood flow in the hemorrhoid itself can become constricted, which can lead to superficial sloughing of the hemorrhoid. There are also cases in which the whole hemorrhoid is sloughed off, leaving an ulcer in its place. As a result of lack of oxygen, the surrounding tissues can die and turn black, causing gangrene.