Picture of the Anus

Human Anatomy

Medically Reviewed by Carol DerSarkissian, MD on June 23, 2021

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The anus is the opening where the gastrointestinal tract ends and exits the body. The anus starts at the bottom of the rectum, the last portion of the colon (large intestine). The anorectal line separates the anus from the rectum.

Tough tissue called fascia surrounds the anus and attaches it to nearby structures.

Circular muscles called the external sphincter ani form the wall of the anus and hold it closed. Glands release fluid into the anus to keep its surface moist.

A plate-like band of muscles, called the levator ani muscles, surround the anus and form the floor of the pelvis. A network of veins lines the skin of the anus.

Anus Conditions

  • Internal hemorrhoids: Swollen veins inside the anus or rectum. These cannot be seen from outside the body.
  • External hemorrhoids: Blood vessels that swell near the opening of the anus or bulge outside.
  • Anal cancer: Cancer of the anus is rare. Infection with human papillomavirus (HPV), anal sex, and multiple sexual partners increase the risk.
  • Anal herpes: Anal sex may spread the herpes viruses HSV-1 and HSV-2. Symptoms include painful sores around the anus that come and go.
  • Anal warts: Infection by the human papillomavirus (HPV) can lead to warts in and around the anus.
  • Anal fistula: An abnormal channel developing between the anus and the skin of the buttocks. Inflammatory bowel disease (Crohn’s and ulcerative colitis) or previous surgery are common causes.
  • Anal fissure: A tear in the lining of the anus, often caused by constipation. Pain, especially with bowel movements, is the main symptom.
  • Anal abscess: A pocket of infection in the soft tissue around the anus. Antibiotics and surgical drainage may be required to effectively treat an abscess of the anus.
  • Anal itching: Itching in or around the anus is a common problem. In most cases, no serious cause is responsible.
  • Proctalgia fugax: Sudden, severe pain in the area of the anus and rectum, lasting seconds or minutes, then disappearing. The cause is unknown.
  • Constipation: Difficulty passing stools is common, and can cause anal pain, anal fissures, and bleeding from hemorrhoids.
  • Anal bleeding: Bright red blood from the anus is sometimes from hemorrhoids, but requires evaluation to rule out a more serious cause.

Anus Tests

  • Physical examination: A doctor may inspect the outside of the anus, and insert a gloved finger to feel for abnormal areas on the inside of the anus.
  • Sigmoidoscopy: An endoscope (flexible tube with a lighted camera on its tip) is inserted into the anus and moved into the colon. Sigmoidoscopy can only reach part of the colon for viewing.
  • Colonoscopy: An endoscope is inserted into the anus, and the entire colon is viewed to look for problems.
  • Fistulography (fistulogram): A liquid that helps improve image contrast is injected into an abnormal opening in or near the anus, and X-ray films are taken. Fistulography can detect an abnormal connection (fistula) between the anus and skin.

Anus Treatments

  • Antibiotics: These may be used to fight infections of the anus caused by bacteria.
  • Antiviral medications: Medicines such as acyclovir (Zovirax), famciclovir (Famvir), and valacyclovir (Valtrex) are used to treat anal infections caused by the herpes viruses HSV-1 and HSV-2.
  • Incision and drainage: Serious skin infections (abscesses) in or around the anus may require this surgical procedure to drain the infected fluid.
  • Anus surgery: Cancer of the anus, anal warts, abscess, or fistula may require surgery to correct the problem.
  • Anal wart treatments: Doctors may use surgery, freezing (cryotherapy), a laser or heat probe, or other treatments to remove warts from the anus.
  • Stool softeners: Constipation may cause hard stools and painful bowel movements. Over-the-counter or prescription stool softeners can relieve these symptoms.
  • Fiber: Increasing fiber in the diet or taking fiber supplements can improve constipation and reduce bleeding from hemorrhoids.
  • Hemorrhoid cream: Over-the-counter or prescription topical medicines can relieve the itching and discomfort caused by hemorrhoids.
  • Hemorrhoid banding: A doctor ties rubber bands around external hemorrhoids, causing the tissue to slowly die and fall off.
  • Hemorrhoid procedures: A doctor may use a laser, heat probe, injections, or other treatment to destroy hemorrhoids and reduce symptoms.
  • Steroid cream: Itching in the anus often responds to over-the-counter creams containing hydrocortisone or a similar steroid medicine.

Show Sources


Feldman, M. Sleisenger and Fordtran’s Gastrointestinal and Liver Disease, Saunders Elsevier, 2010.

Goldman, L. Cecil Medicine, Saunders, 2007.

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