Generally speaking, hemorrhoids are not dangerous and complications are extremely rare. That said, if and when complications do occur, actions must be taken immediately to increase chances of healing and avoid any further problems. Complications vary from strangulated and prolapsed internal hemorrhoids to blood clots and thrombosed external hemorrhoids to anemia and various infections.
Strangulation is a complication of internal hemorrhoids and occurs when the hemorrhoid becomes trapped by the anal muscles, thereby blocking the arteries and cutting off the supply of blood. Prolapse is defined as falling down or slipping out of place and occurs when the blood vessels swell and extend from their position in the rectum through to the anus. Both strangulated hemorrhoids and prolapsed hemorrhoids can cause unbearable pain and intense discomfort when sitting or passing a bowel movement.
Blood clots are most often a complication of external hemorrhoids, the medical term for which is thrombosis. Simply put, thrombosis is the formation of a blood clot, or a thrombus, within a blood vessel which prevents blood from flowing normally through the circulatory system. When this occurs, the hemorrhoid is termed a thrombosed external hemorrhoid. Such blood clots can cause increasingly unbearable pain and itching. In the event that a thrombosed hemorrhoid ruptures, more bleeding and pain may be caused, although the site of the rupture does usually heal on its own.
Anemia is a condition that develops when there are too few healthy red blood cells or hemoglobin in the blood. In the context of hemorrhoids, people may develop anemia due to chronic blood loss since common hemorrhoid symptoms include bleeding from the anus and fresh blood in the stool. If hemorrhoids bleed too much and deprive the red blood cells of oxygen, the blood supply ends up carrying less oxygen around the body and this can then lead to fatigue, shortness of breath, headaches, and dizziness.
Infection occurs when bacteria gets into a hemorrhoid that is bleeding and infects the tissue. The risk of this happening is typically greater for internal hemorrhoids due to the reduction of healthy circulation to the rectum for strangulated hemorrhoids and the blood flow issues that are associated with prolapsed hemorrhoids. In many cases, infected hemorrhoids are the result of pre-existing conditions such a diabetes, Crohn’s disease, obesity, atherosclerosis, blood clots, or any conditions which weaken the immune system such as HIV. In addition to the typical symptoms of hemorrhoids, an infection can bring on symptoms such as fever, pain that worsens over time, and redness around the anus. When left untreated, infections can lead to tissue death, abscesses, fever, and peritonitis.
Given the dangers and complications associated with hemorrhoids, it is important to see a doctor or seek other medical attention if you experience blood in your stool or profuse rectal bleeding accompanied by feelings of dizziness or faintness. Neither of these are typical symptoms of hemorrhoids and may be an indication that something more serious is going on. Additional warning signs include mucus or pus from the rectum, fever or chills, a rapid heartbeat, or nausea.
Resources:
1) https://www.healthline.com/health/types-of-hemorrhoids#complications
2) https://www.webmd.com/a-to-z-guides/understanding-anemia-basics#1
3) https://www.verywellhealth.com/hemorrhoids-signs-symptoms-and-complications-4160936