External hemorrhoids can be felt as bulges at the anus, but they usually cause few of the symptoms that are typical of internal hemorrhoids. External hemorrhoids can cause problems, however, when blood clots inside them. This is referred to as thrombosis. Thrombosis of an external hemorrhoid causes an anal lump that is very painful and tender, and often requires medical attention. The thrombosed hemorrhoid may heal with scarring, and leave a tag of skin protruding in the anus. Occasionally, the tag is large, which can make anal hygiene (cleaning) difficult or irritate the anus.