An anal fistula is a small tunnel between the anal canal and the skin near the anus, usually left behind after an abscess. It will not heal on its own because the internal opening keeps letting in stool and bacteria, repeatedly re-infecting the tract. Surgery is almost always needed to clear the tunnel and cure it.
An anal fistula is a small abnormal tunnel that forms between the inside of the anal canal or lower bowel and the skin near the anus. It usually develops after an infection in one of the tiny glands inside the anus leads to an abscess, a collection of pus, which then drains and leaves a persistent channel behind. Unlike a simple cut or graze, a fistula rarely closes up and heals by itself, and this is one of the most common questions patients ask. Understanding why is the key to understanding why treatment almost always involves a procedure. Anal fistulas are not dangerous in most cases, but they are uncomfortable, tend to leak and flare up repeatedly, and can slowly worsen if ignored. This guide explains what a fistula is, why it persists, how it is treated, and what recovery involves. Many people feel awkward discussing symptoms in this part of the body, but a fistula is a well-understood surgical problem that surgeons deal with routinely, and seeking help early usually makes treatment simpler and recovery smoother. You can also read more on our anal fistula information page.
What is an anal fistula?
An anal fistula is an abnormal narrow tunnel connecting the inside of the anal canal to the skin around the anus. It most often forms as the aftermath of an anal abscess, an infected pocket of pus. Once the abscess drains, the tract that is left behind can remain open, discharging fluid or pus and refusing to heal.
Why won't an anal fistula heal on its own?
An anal fistula rarely heals by itself because the tunnel is continually kept open from the inside. The internal opening allows stool, bacteria, and moisture to keep passing into the tract, so the channel is repeatedly re-infected and cannot close. The outer skin may seem to heal over, only for the abscess and discharge to return a while later.
To picture why a fistula persists, it helps to think of the tunnel as having two openings: an internal one inside the anal canal, usually at the site of the gland where the original infection began, and an external one on the skin, where the abscess once drained. As long as that internal opening remains connected to the inside of the bowel, a small amount of stool and the bacteria it contains keeps seeping into the tract. This constant, low-level contamination means the body simply cannot keep the channel clean long enough for it to heal from the inside. Sometimes the external opening on the skin closes over for a while, giving the impression that the problem has resolved, but because the source inside has not been dealt with, pressure and infection build up again, a fresh abscess forms, and the discharge returns. This pattern of apparent healing followed by another painful flare-up is very typical of a fistula and is exactly why antibiotics or simply waiting will not cure it. It can help to think of an abscess and a fistula as two phases of the same problem: the abscess is the acute, painful infection, while the fistula is the chronic tunnel that can be left behind once the abscess settles or is drained. Not everyone who has an abscess goes on to form a fistula, but a significant number do, which is why any drainage of an abscess is usually followed up to check whether a tract has persisted. Surgeons also classify fistulas by how their path relates to the sphincter muscles, and this classification guides which treatment is safest. The only reliable way to resolve a fistula is a procedure that deals with the tract and its internal opening. You can read more about how fistulas are assessed and managed on our anal fistula page, where the different surgical approaches are explained.
What causes anal fistulas?
The great majority of anal fistulas begin with an infection in one of the small glands inside the anus, which develops into an abscess. When the abscess drains, a tunnel is left behind. Less commonly, fistulas are linked to underlying conditions such as Crohn's disease, tuberculosis, previous surgery or injury, or certain infections in the region.
- A previous or current anal abscess, which is by far the most common cause
- Blocked, infected anal glands inside the anal canal
- Crohn's disease and other forms of inflammatory bowel disease
- Tuberculosis and some other specific infections
- Injury or trauma to the anal area, or complications of previous surgery
- Radiation treatment to the pelvic region
- Rarely, certain cancers of the anal or rectal region
What are the symptoms of an anal fistula?
Common symptoms include a persistent or recurring discharge of pus or blood from an opening in the skin near the anus, ongoing throbbing pain that may worsen when sitting or passing a stool, and repeated abscesses that flare and settle. The skin around the opening is often irritated, swollen, or tender to the touch.
- A small opening in the skin near the anus that leaks pus, blood, or fluid
- Persistent throbbing or aching pain, often worse when sitting down
- Recurring painful swellings or abscesses that come and go
- Skin irritation, itching, or soreness around the anus from constant discharge
- An unpleasant smell from the discharge
- Pain or bleeding when passing a stool
- Feeling generally unwell or feverish during a flare-up
How is an anal fistula treated?
Anal fistulas are treated surgically, because a procedure is needed to clear the tract and close its internal opening. The right operation depends on how the tunnel runs in relation to the sphincter muscles. Options range from laying the tract open to muscle-sparing techniques, seton threads, and newer minimally invasive approaches. Your surgeon will recommend the safest choice.
The central challenge in fistula surgery is curing the tunnel while protecting the ring of sphincter muscles that keep you continent, because these muscles often lie close to or within the fistula's path. For a simple, low fistula that involves little muscle, a fistulotomy, which means carefully laying the tract open so it can heal from the base upwards, is straightforward and very effective. When a fistula passes through a significant amount of muscle, cutting it directly would risk affecting bowel control, so muscle-sparing methods are chosen instead. One common step is the placement of a seton, a soft thread passed through the tract that keeps it draining, controls infection, and allows the surgeon to treat it safely in stages. Other techniques include advancement flaps, which cover the internal opening with healthy tissue, the LIFT procedure, and minimally invasive laser or plug-based approaches that aim to seal the tract with less disturbance to the muscle. Because every fistula is different, an accurate picture of its course is essential, and an MRI scan or an examination under anaesthetic is sometimes used to map it before deciding on the best approach. Antibiotics may help settle an acute infection, but they do not cure the fistula on their own. The most suitable operation is very much an individual decision, balancing the best chance of cure against protecting continence. For a complex fistula, treatment is sometimes carried out in stages rather than all at once: a seton may first be placed to calm the infection and let inflammation settle, with the definitive repair performed weeks or months later when conditions are more favourable. This staged approach can feel slow, but it is often the safest route to a lasting cure while keeping the muscle intact. Your surgeon will talk you through the likely number of steps and set realistic expectations from the outset. If you have a fistula or a recurring abscess, please book a consultation so your surgeon can examine you and explain the options.
What is recovery like, and can a fistula come back?
Recovery after fistula surgery is usually manageable, with most people going home the same day and returning to normal activities within a week or two, though full healing of the wound can take several weeks. Keeping the area clean, taking warm sitz baths, and maintaining good stool habits all help. Fistulas can occasionally recur, which is why follow-up matters.
In the weeks after surgery it is normal to have some discomfort, a little bleeding, and a discharge from the wound as it heals gradually from the inside out; your team will explain how to keep the area clean and may recommend regular warm baths to soothe it and keep it comfortable. Simple pain relief, a high-fibre diet, and plenty of fluids help keep bowel movements soft so that passing a stool is less painful and the healing tissue is not disturbed. If a seton has been placed, it may stay in position for some weeks or months and will be managed at your follow-up visits. Most fistulas are cured with appropriate treatment, but there is always some chance of recurrence, particularly with complex fistulas or when an underlying condition such as Crohn's disease is involved, so it is important to attend your review appointments and to report any return of pain, swelling, or discharge promptly. Looking after your general bowel health and dealing with any flare of an underlying condition also reduce the risk of the problem returning. Practical wound care makes a real difference in these weeks: gentle showering or bathing rather than harsh scrubbing, patting the area dry, wearing loose cotton underwear, and using a soft pad if there is discharge all keep you comfortable and lower the risk of skin irritation. Many people can return to office work within a week or two, though jobs involving heavy lifting or long periods of sitting may need a little longer, and you should follow your surgeon's specific advice. It is natural to feel low or self-conscious while a wound in this area heals slowly, but the discharge steadily reduces as healing progresses, and reaching a full cure is the usual outcome. If you notice signs that a fistula may be coming back, do not wait for it to worsen; arrange to be reviewed. You can book an appointment for a thorough assessment and a clear plan.
This article provides general educational information only and is not a substitute for a professional medical consultation. An anal fistula will not heal on its own and tends to worsen the longer it is left, but with the right surgical care the outlook is very good and most people are cured. If you have a recurring abscess, discharge, or pain near the anus, please book an appointment with Dr. Sujan Shrestha for a confidential assessment and tailored advice.