Anal Fistula

An anal fistula is usually a side effect of an anal abscess, an infected wound that drains pus from your anus. The draining abscess can create a tunnel through your anus to the skin outside. Anal pain, swelling and redness are the primary symptoms. Surgery is the primary treatment.


Anal fistula leading from the wall of the anal canal to the outside skin of the buttocks.
A fistula is a tunnel that develops where it shouldn’t. An anal fistula travels through your anal wall to the skin outside.

What is an anal fistula?

An anal fistula is an abnormal passageway that develops from inside your anus to the skin outside. It usually develops in the upper part of your anus (butthole), where your anal glands are. When these glands become infected, drainage from the infection can create a fistula. This infection is called a perianal abscess. (Sometimes an anal fistula is also called a perianal fistula. “Perianal” means in the region of your anus.)

How common is this condition?

A fistula is a relatively common anorectal condition. It’s twice as common in men and people assigned male at birth (AMAB). About half of people who get an infected anal gland will develop a fistula. An infected gland that forms an abscess, a pocket of pus that needs to drain, causes 75% of anal fistulas.


Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy

Symptoms and Causes

What are anal fistula symptoms?

The most common anal fistula symptoms are:

  • Anal pain, often intense and throbbing. You may feel it more when you poop, cough or sit. Your butt may be sensitive to touch.
  • Swelling and redness (inflammation) inside or around your anus. These are signs of active infection under the skin (cellulitis).
  • Fluid drainage from somewhere around your anus. It may include pus, poop or blood (rectal bleeding). It may have a smell.

Less common symptoms include:

You may or may not be able to see the fistula with a mirror.

What does an anal fistula look like?

An anal fistula looks like a hole in the skin near your anus. The hole is actually the outermost portion of the tunnel, which connects to the abscess inside. It might ooze drainage, like pus, blood or poop, especially when you touch the skin around it. Some older fistulas may close at the opening, while the rest of the tunnel remains. This causes pain and swelling until the fistula reopens to let out the drainage.


What is the main cause of a fistula?

Fistulas can occur throughout your body, either between different organs or from an organ to an opening in your skin. They usually occur when your tissues are inflamed for a long time, due to an injury or disease. Chronic inflammation and infection can eventually erode into the nearby tissues, especially when pus needs to drain. This can create a channel between the wound and nearby tissues.

What causes an anal fistula?

The most common cause of an anal fistula is a perianal abscess, which usually forms over an infected anal gland. An abscess is a pocket of pus that develops at the site of an infection. The pus needs to drain away and may create its own drainage channel to the outside. Sometimes, a healthcare provider creates a drainage channel to treat the abscess. But often, the wound doesn’t heal completely, leaving a fistula. Uncommon causes of anal fistulas include:

What are the risk factors for getting an anal fistula?

You’re more likely to get an anal fistula if you:

  • Were assigned male at birth.
  • Have or have had a perianal abscess in the past.
  • Have an inflammatory bowel disease (IBD) such as Crohn’s.
  • Have a history of surgery or radiation therapy in your perianal region.
  • Are immunocompromised or prone to more frequent infections.
  • Have a chronic STI.


What are the possible complications of an anal fistula?

A fistula that goes untreated generally won’t heal on its own. This can lead to long-term complications, such as:

  • Persistent infection. A fistula that stems from an abscess or infection may keep the infection active. The infection may seem to go away at the original site but then return, forming a new abscess and causing renewed pain. Sometimes, the fistula may seem to be healing and may close at the opening, but recurring infection and drainage later open it again in a repeating cycle.
  • Fistula extension. A chronic fistula may rarely extend in new directions, creating new branching channels and openings in your skin. These complex fistulas are more difficult to repair.
  • Cancer. Anal cancer has occasionally been found in longstanding anal fistulas that have been present for years. Chronic inflammation and erosion are known risk factors for cancer.

Diagnosis and Tests

How is an anal fistula diagnosed?

Healthcare providers can find most anal fistulas during a physical exam, but sometimes the opening to the outside is closed. Your provider will also want to find the inside opening to the fistula, within your anus. This part might require anesthesia. If it hurts too much for your provider to touch or open your anus to examine the inside, they may have to examine you in the operating room under sedation.

To find the inside source of the fistula, your provider may use a lighted scope, like an anoscope or proctoscope (a longer scope that can visualize your rectum). Sometimes, they’ll inject hydrogen peroxide into the external opening to find the infection at the source of the fistula. The peroxide will interact with the infection and create bubbles or foam at the site. Finding the inside source can confirm the fistula.

Will I have any other medical tests?

Your healthcare provider might need to take imaging tests (radiology) to see the path of your fistula. This might mean:

  • MRI (magnetic resonance imaging). An MRI is a noninvasive imaging test that provides high detail. This can help providers map the path of the tunnel and also see how it interacts with your muscles and other organs.
  • Endoscopic ultrasound. As an alternative to MRI that produces similar images, an endoscopic ultrasound goes inside your anus with a tiny lighted camera and a tiny ultrasound probe.
  • Fistulography. A fistulogram is an X-ray of your fistula that your healthcare provider takes after injecting dye into it. The dye will highlight the path of the fistula.

Your provider needs to know the pathway of your fistula in order to determine how to treat it. They’ll classify your fistula by its pathway.

What are the different types of anal fistulas?

Healthcare providers classify anal fistulas by where they’re located in relation to your anal sphincter muscles. These are the muscles that control your bowel movements, so it’s important to protect them. Your provider might refer to your anal fistula by a specific name based on its location, such as:

  • Intersphincteric anal fistula: Passes through your internal anal sphincter muscle and then burrows out through the space between your internal and external sphincter muscles.
  • Transsphincteric fistula: Travels through both layers of your anal sphincter muscles.
  • Suprasphincteric fistula: Passes through your internal sphincter and then goes around your external sphincter.
  • Extrasphincteric fistula: Goes around both sphincter muscles. This less common type usually originates from your rectum rather than your anus, so it doesn’t come from an anal gland.
  • Superficial anal fistula: Travels from the lower part of your anal canal, below your anal glands, through the skin nearby, bypassing your muscles. This type doesn’t come from an anal gland.

You don’t have to know or remember what type of anal fistula you have, but the type will influence how your provider treats it. If it involves much of your sphincter muscles, the treatment might be more complicated. They have to be careful not to injure these muscles when they fix your anal fistula.

Management and Treatment

What is the treatment for an anal fistula?

Most anal fistulas will require surgery to fix. Spontaneous healing is usually followed by recurring infections and abscesses that reopen the fistula. However, if your fistula is caused by inflammatory bowel disease and isn’t infected, it’ll occasionally heal with medical treatment. Your provider might try treatment with an immunomodulator, like infliximab, before resorting to surgery for these fistulas.


Anal fistula surgery can be simple or complex, depending on how simple or complex the fistula is. The most common anal fistulas are simple, intersphincteric fistulas, which only involve a small amount of muscle. These are safe to treat in a single operation. More complex fistulas may need surgery in stages.

Simple fistulas

If your anal fistula involves only a minimal amount of muscle and doesn’t have any branches, it’s considered a simple fistula. The surgical treatment for a simple fistula is called a fistulotomy. This one-and-done procedure is the easiest and the most effective way to treat an anal fistula (about 95%).

Fistulotomy: Your colorectal surgeon will cut through the roof of the fistula, allowing it to fill in from the bottom up. They might also remove infected tissue. Cutting through the roof may mean cutting through a small amount of muscle, but a little is OK. Cutting too much muscle risks damaging your bowel control.

Complex fistulas

Your fistula is considered complex if it involves a significant amount of muscle, if it has branches or if you have preexisting conditions that raise your risk of complications from surgery. Complex fistulas may require multiple surgeries to fix. Your colorectal surgeon may use one or more of these techniques:

  • Seton drain. A seton is a type of surgical thread that isn’t absorbed over time but must be removed. A surgeon loops the seton through your fistula to help keep it open long enough to drain all the discharge out. A seton can also slowly cut through the fistula tract, allowing the tissue to heal as it cuts through the muscle. Lastly, it helps with local scarring of the tissue so that the wound doesn’t pull apart later. Your surgeon may later remove the drain and close the fistula with a fistulotomy or another procedure. If your fistula is caused by a chronic condition, like inflammatory bowel disease, your surgeon might leave the seton drain in place indefinitely.
  • Endorectal advancement flap. This procedure avoids cutting into the roof of the fistula so your sphincter muscles stay intact. Instead, your surgeon cuts out the infected tissue around the inside opening of your anal fistula. Then they cover this opening by pulling down a flap of healthy tissue from the inside of your rectum above it. The fistula should continue to drain out of the outside opening and then begin healing from the inside out. This procedure is considered about 70% effective, but in some cases, the infection and fistula still come back. There’s also still some risk (approximately 30%) of injuring the sphincter muscle when cutting the flap.
  • LIFT procedure. LIFT stands for “ligation of intersphincteric fistula tract”. This means closing (ligation) the part of the fistula that passes between your two sphincter muscles (intersphincteric), usually with stitches. Your surgeon may then remove the entire fistula tract from this space or scrape out the infected tissue inside. This procedure usually follows a seton drain procedure. It’s a little less effective than fistulotomy (75%) but it doesn’t risk harming your sphincter muscles.
What are the risks of anal fistula surgery?

The main risks are:

  • Recurring infection. If the infection isn’t completely gone from your fistula, it may continue inside your healing fistula. Antibiotics can usually treat a recurring infection.
  • Recurring fistula. An anal fistula may come back after surgery if it doesn’t heal completely. This might be because of underlying chronic conditions, or because of the technique used.
  • Fecal incontinence. Some people experience slightly compromised fecal continence after anal fistula surgery. For example, they might have trouble holding in gas or have some fecal leakage. These complications are less common with more experienced colorectal surgeons.
What is recovery like from anal fistula surgery?

Anal fistula procedures are generally outpatient procedures, so you can go home the same day, although some people will need to return for more surgery later. You’ll have prescription pain medication to take home with you, along with some instructions for self-care. These may include:

  • Water and fiber supplements. Pain medications can cause constipation, so your provider might prescribe fiber supplements to prevent this. It’s important to take these with lots of water.
  • Sitz bath. Soaking your anus in a sitz bath (a warm, shallow bath) at least once a day will help soothe it and quicken healing.
  • Wound management. You may need to apply dressings to your wound to collect drainage and change them often to keep it clean.

Outlook / Prognosis

What should I expect if I have an anal fistula?

Your outlook will depend on how simple or complex your anal fistula is. This determines how extensive the treatment and recovery process will be. In general, you can expect to spend three to six weeks recovering from one or several surgeries. Some fistulas return after surgery, especially if they had many branches or they were caused by a chronic condition. Some people with IBD get multiple anal fistulas.

Living With

When should I see my healthcare provider about an anal fistula?

Always see a healthcare provider about anal pain. Anorectal conditions that cause significant pain may be serious. Don’t assume it’s something that will go away by itself. Hemorrhoids may be more common and familiar, but they aren’t usually very painful. If a general (primary care) practitioner tells you it’s a hemorrhoid but the pain continues, see a specialist, like a gastroenterologist or colorectal surgeon.

Additional Common Questions

What is a perianal vaginal fistula?

A perianal vaginal fistula is usually called a rectovaginal fistula, because it usually connects from your rectum to your vagina. Your rectum is the part of your large intestine that comes just before your anus. The border between your rectum and vagina is much narrower than between your vagina and anus. A vaginal fistula can develop from any part of your intestines, but it’s usually from your rectum or colon.

What's the difference between an anal fissure vs anal fistula?

An anal fissure is a split or tear in the lining of your anal canal. It can cause similar symptoms to an anal fistula, but a fissure is a superficial wound. It doesn’t tunnel through your anal wall to your skin the way a fistula does. However, it’s possible that an anal fissure could develop into an anal fistula. If an anal fissure becomes infected, it could form an abscess, which could create an anal fistula when it drains.

A note from Cleveland Clinic

Severe anal pain can be both physically and psychologically debilitating. Not only does it haunt you every time you sit or visit the toilet, but it may feel like a difficult thing to discuss with a healthcare provider. Don’t let this stop you. Anorectal diseases and conditions deserve the same attention as any other. An anal fistula needs treatment, and the sooner you get it, the simpler that treatment is likely to be.

Medically Reviewed

Last reviewed on 07/11/2023.

Learn more about our editorial process.

Appointments 216.444.7000