Hemorrhoids can occur both inside and above the anus (internal) or under the skin around the anus (external). Hemorrhoids arise from congestion of internal and/or external venous plexuses around the anal canal.
It is not known why hemorrhoids enlarge. Hemorrhoids may result from straining to move stool. Other contributing factors include pregnancy, aging, chronic constipation or diarrhea, and anal intercourse.
Pregnancy is a clear cause of enlarged hemorrhoids though, again, the reason is not clear.
Hemorrhoids can occur for the following reasons:
• pregnancy
• aging
• chronic diarrhea
• chronic constipation
• straining to move stool (related to the previous one)
• sitting for long periods (especially sitting for long periods at a time in the toilet)
• anal intercourse
• obesity
• genetics - some people inherit a tendency to develop hemorrhoids
Tumours in the pelvis also can cause an enlargement of hemorrhoids by pressing on veins draining upwards from the anal canal.
It is also thought that using force to pass a stool, particularly a hard stool, through the anal canal can drag the hemorrhoidal cushions downward and enlarge them.
Another theory suggests that with age or an aggravating condition, the supporting tissue that is responsible for anchoring the hemorrhoids to the underlying muscle of the anal canal deteriorates. Therefore, with time, the hemorrhoidal tissue loses its mooring and slides down into the anal canal.
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