Severe pain is not a common symptom of internal hemorrhoids, because internal hemorrhoid happens in the area above the dentate line that is supplied by the visceral nerve, like those found within the intestines, which sense pressure rather than pain.
As the venous complex of an internal hemorrhoid becomes varicose and continues to enlarge, it bulges into the anal canal and loses its normal anchoring, becoming a prolapsing internal hemorrhoid. The prolapsing hemorrhoid usually returns into the anal canal or rectum on its own, or can be pushed back inside using one’s finger, but usually prolapses again after the next bowel movement. In the anal canal, a hemorrhoid is exposed to movement caused by passing stool, particularly hard stools that can cause bleeding and pain. The painless rectal bleeding with bright red blood is a common symptom of internal hemorrhoids. The rectal mucosal lining that has been pulled down secretes mucus and moistens the anus and its surrounding skin, while the stool itself can also leak onto the anal skin. Itchiness often occurs as a result of this dual presence of stool and moisture.
In general, symptoms of external hemorrhoids are different than those of internal hemorrhoids. External hemorrhoids can be felt as bulges at the anus, but rarely display any of the same symptoms seen with internal hemorrhoids. They will cause problems, however, if the varicose vein complex ruptures, as blood clots occur and build up the pressure inside the lump. This condition, known as thrombosed external hemorrhoid, causes an extremely painful bluish anal lump and often requires medical attention. The somatic nerve in the anal canal (below the dentate line) can sense pain, this is why the patients feel significant pain when they develop thrombosed external hemorrhoids. Thrombosed hemorrhoids may heal with scarring and leave a tag of skin protruding from the anus. Occasionally, the tag turns out to be quite large, which can make anal hygiene (cleaning) difficult or irritate the anus.