Hemorrhoids are classified as internal or external, based on where they start. Usually hemorrhoids that protrude out through the anus have their base above the pectinate line, so they actually are internal hemorrhoids. Sometimes these prolapsed hemorrhoids will come down and then go back up; and other times, they will stay down.
External - may thrombose (bluish nodules), resolve after few days and retract leaving skin tags. Internal - prolapse through anal sphincter may cause strangulation, thrombosis, gangrene. Mixture of both (most common).
Internal hemorrhoids develops under the mucous membrane at the lower edge of the rectum Internal hemorrhoids bleeds but does not hurt;
These hemorrhoids are easy to treat because they start in an area where there are no pain fibers. The "line" is visible to the physician during the examination
External hemorrhoids develops under anal epithelium of the anus (outside the dentate line). External hemorrhoids does not bleed but hurts badly when swollen.