Anus

What is the anus?

Your anus is the end of your large intestine — the last three or four centimeters of it. This is where your large intestine opens to the outside to let your poop come out. At your anus, the tissue lining the inside of your large intestine begins to change from tender mucosa to normal skin. Ring-like muscles called sphincters surround your anus and keep it closed until they’re activated to let your poop come out.

What is the difference between the anus vs. the rectum?

Your rectum is the section of your large intestine that comes just before your anus. It’s about five or six inches long. This is the reservoir where poop collects before it’s ready to come out. When your rectum is full, nerves trigger the urge to have a bowel movement, and your internal anal sphincter relaxes automatically. Your external sphincter is under your conscious control to activate when you’re ready.

What is the function of the anus?

Your anus facilitates your bowel movements. Nerves and muscles surrounding your anus coordinate to tell you when you need to poop, while allowing you to hold it in until you’re able to reach a toilet. When you’re ready, these nerves and muscles coordinate again to push poop out of your body. The mucous lining in your anus secretes mucus to lubricate the passage and help your poop pass smoothly through.

What is the anatomy of the anus?

A row of vertical folds in the inside lining divides your anus into upper and lower parts. The folds form columns (anal columns) that are separated by grooves (anal sinuses) that end in smaller folds (anal valves). Your anal sinuses contain mucus-secreting glands. The valves mark the end of the sinuses and the dividing line where the mucous lining begins changing into skin (the pectinate line or dentate line).

The upper and lower parts of your anus (above and below the pectinate line) have different vascular supply and nerve supply. This is why your anus is much more sensitive to pain and other sensations below the line (in the lower two-thirds). Your internal and external anal sphincters also have a different nerve supply, which is why the inner one is involuntary (out of your control) and the outer one is under voluntary control.

What are the common conditions and disorders that affect the anus?

Anal conditions and disorders include:

• Hemorrhoids. Hemorrhoids are swollen blood vessels in your anus or rectum. They’re called internal hemorrhoids above the pectinate line, and external hemorrhoids below it.
• Anal fissure. An anal fissure is a tear in your anus lining. It can cause pain and bleeding.
• Anal yeast infection. A Candida infection (Candidiasis) can cause itching and pain in or around your anus (your perianal region).
• Anal STIs. Sexually transmitted infections and diseases can affect your anus through anal sex, including anal penetration, oral and digital (finger) stimulation. Anal STIs include chlamydia, genital herpes, human papillomavirus (anal warts), syphilis, gonorrhea, hepatitis A, hepatitis B and HIV.
• Anal abscess/anal fistula. When an anal gland becomes clogged and infected, an abscess, or pocket of pus, forms under your skin. More than half of drained anal abscesses leave behind an anal fistula, an abnormal, tunnel-like passageway leading from the gland to your outer skin.
• Anal stenosis. Stenosis is when one of your body canals narrows, usually due to scar tissue on the inside. Injury, surgery or disease can cause scarring inside your anus that leads to stenosis.
• Anorectal malformation. An anorectal malformation is a birth defect that causes your anus to develop abnormally. A missing or misplaced anus may need surgical repair (anoplasty).
• Anismus. Anismus happens when the muscles and nerves involved in pooping can’t coordinate correctly to make a bowel movement. It’s also called dyssynergic defecation.
• Anal incontinence. Fecal incontinence can occur when your anal sphincter muscles fail to control your bowel movements. It can cause poop to come out when you don’t want it to.
• Anal cancer. Anal cancer is a separate disease from rectal or colon cancer. Cancer that develops in your anal canal is usually squamous cell carcinoma.

What are the signs or symptoms of possible health issues in the anus?

You should see a healthcare provider if you notice symptoms such as:

• Anal pain. Pain in your anus could be a sign of many different conditions.
• Anal lesions. Warts, rashes, bumps, sores and tears can appear in and around your anus.
• Anal itching. Itching in and around your anus could be related to an allergy or infection.
• Anal bleeding. You might notice bleeding from your anus when you go to the bathroom or when you wash or scratch your anus. Bleeding may be painful or not, depending on the cause.
• Anal discharge. Mucus or pus in your poop or in your underwear might be a sign of disease.
• Difficulty with bowel movements. Difficulty getting poop out or holding poop in might involve your anal muscles. Missing or excessive bowel movement urges might involve your nerves.

What tests do healthcare providers use to check on the health of the anus?

Anal exams include:

• Digital rectal exam. A digital (fingers) rectal exam is a physical exam using lubricated gloved fingers inside your anus and rectum.
• Anoscopy. An anoscopy uses a small scope to look inside your anal canal. Sometimes, it uses a high-resolution magnifier with the scope.
• Barium enema. This is a gastrointestinal X-ray exam that looks inside your colon, rectum and anus. It takes real-time video X-rays, called fluoroscopy. A barium enema helps your insides show up better in images. A technician will inject the barium into your anus.
• Defecography. A defecography takes X-rays of your body mechanics as you poop. It’s used to identify mechanical and functional pooping disorders.
• Anorectal manometry. This test measures your anal muscle contractions and tests your level of anal sensation and nerve response, as well as muscle control.
• Electromyogram. Electromyography (EMG) tests the electrical activity in your muscles. It can help diagnose issues with your anal sphincters.

How can I keep my anus healthy?

You can help take care of your anus by:

• Practicing safe sex. Screen your partners before sex, and when in doubt, use protection to prevent STIs. Use lubrication to prevent injuring your anal tissues.
• Eating plenty of fiber. Whole foods, especially plants, are an important source of dietary fiber, which helps keep bowel movements smooth and regular.
• Practicing gentle hygiene.Wash and wipe well, but don’t use harsh soaps or wet wipes, which can disturb the sensitive skin and mucosa in your anus.
• Taking symptoms seriously. Don’t be too embarrassed to contact a healthcare provider about symptoms in your anus and get the care you need.

A note from Cleveland Clinic

Your anus is a gateway between your insides and the outside. This gives it an important role in your health. It opens to let food waste come out at the end of its journey through your digestive tract. It also closes to keep infections out. Your anus is small, but if it’s injured or not working well, the symptoms and repercussions might be large. Don’t hesitate to seek care for conditions affecting your anus.