Conditions that may cause anal discomfort include:
Anal abscess and fistula: These problems cause swelling and tenderness near to the anus due to a bacterial infection, sometimes causing a fever or causing pus to drain from an opening in the skin near to the anus.
Anal stricture: The anus is normally muscular, but flexible. A stricture is a band of scar tissue that can prevent the anus from opening to a normal size in order to allow stool to pass easily. An anal stricture may cause pain when passing stools, even thin stools.
Crohn's disease: This autoimmune illness can cause inflammation in any part of the digestive tract, including the anus. It can cause a fissure (a sensitive break in the skin at the anal opening) or a fistula (an infected area that drains through a small hole in the skin).
Hemorrhoids: Hemorrhoids are enlarged veins just under the anal surface. They can cause burning, itching and irritation at the anus. You may be able to feel hemorrhoids as a swelling or lump protruding out of the anus during or after a bowel movement. Bright red blood on the toilet paper or red blood that streaks the stool may come from hemorrhoids.