Anal fistulas

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What is this information about?

This leaflet provides information about anal fistulas and their treatment, including the use of a seton. 

It explains:

• What an anal fistula is  
• What causes it  
• Common symptoms  
• Types of fistulas  
• Treatment options  
• What a seton is and how it works  
• Recovery and day-to-day care  
• When to seek medical help  

Why have I been given this information?

You have been given this leaflet because you have been diagnosed with an anal fistula or are being assessed or treated for one. 

Anal fistulas usually require medical or surgical treatment, and this information will help you understand your condition and what to expect. 

What is an anal fistula?

An anal fistula is an abnormal tunnel that forms between:

• The inside of the anal canal (the end of the bowel), and  
• The skin around the anus

It may appear as a small opening or sore near the anus. Sometimes it is not visible but can cause discharge or irritation. 

What causes an anal fistula?

The most common cause is an anal abscess (a collection of pus caused by infection).

• Around 3 in 4 fistulas develop after an abscess  
• Small glands in the anal canal can become blocked and infected  
• When the abscess drains, a tunnel (fistula) may remain  

Other causes include: 

• Crohn’s disease (a type of inflammatory bowel disease)  
• Previous surgery or injury  
• Radiotherapy  
• Infections (including some sexually transmitted infections)  
• Rarely, cancer  

What are the symptoms of an anal fistula?

Common symptoms include: 

• Pain around the anus  
• Pus or discharge, sometimes with blood  
• Irritation or itching  
• A foul-smelling discharge  

If an abscess is present, you may also have: 

• Swelling  
• Fever  
• Increasing pain  

In more complex cases, symptoms may include: 

• Difficulty controlling bowel movements  
• Passing small amounts of stool through the fistula  

Symptoms may improve when the fistula drains, but often return if it does not heal. 

Are there different types of fistulas?

Yes, fistulas can vary in complexity. 

Low (simple) fistulas

• Close to the skin  
• Involve little or no muscle  
• Easier to treat  

High (complex) fistulas

• Pass through or near important muscles  
• More difficult to treat  
• May require staged treatment 

Some fistulas can also form between the bowel and the vagina (rectovaginal fistula), which may cause:

• Passing gas through the vagina  
• Discharge or stool from the vagina  
• Recurrent infections  

Is an anal fistula dangerous?

Anal fistulas are not usually life-threatening, but they rarely heal on their own. 

Treatment aims to: 

• Control infection  
• Allow drainage  
• Close the fistula  
• Protect the muscles that control bowel function  

What are the treatment options?

Treatment depends on the type of fistula and whether there is infection. 

If there is an abscess

Urgent treatment is required and may include: 

• Drainage of the abscess  
• Placement of a seton (a soft thread to allow drainage)  

At this stage, the focus is on controlling infection, not closing the fistula. 

Planned (elective) treatment

Once infection has settled: 

Low (simple) fistulas 

• May be treated by fistulotomy (opening the tract so it can heal)  

Complex fistulas 

Treatment options may include: 

• Seton drainage  
• Fistulotomy (in selected cases)  
• LIFT procedure (closing the tract without cutting muscle)  
• Advancement flap surgery  
• VAAFT (keyhole surgery)  
• Medications (biologics), especially for Crohn’s disease  

Your surgeon will discuss the best option for you. 

What is a seton?

A seton is a soft thread or loop placed through the fistula. 

It is designed to: 

• Keep the fistula open  
• Allow continuous drainage  
• Reduce infection  
• Protect the surrounding muscles  

A seton does not cure the fistula but helps control symptoms while further treatment is planned. 

How is a seton placed?

A seton is placed during a procedure under general anaesthetic. 

It is designed to: 

• You will be asleep during the procedure  
• It is usually a day-case procedure  
• The seton is passed through the fistula and tied externally  

The seton may stay in place for several months.

What should I expect after a seton is placed?

You may experience: 

• Mild discomfort or soreness  
• A feeling of a small knot or tugging sensation  
• Ongoing discharge (this is normal)  

Pain is usually managed with simple pain relief such as paracetamol or ibuprofen. 

You may be advised to gently move (“wiggle”) the seton during washing to prevent blockage. 

Can I have more than one seton?

Yes. 

Some people have multiple fistula tracts, and more than one seton may be needed. This reflects the complexity of the condition and is not unusual. 

What are the possible complications?

Most people tolerate setons well, but possible complications include:

• Irritation or discomfort  
• Minor bleeding  
• Infection or abscess  
• Seton moving or falling out  
• Recurrence or worsening of the fistula  

Contact your healthcare team if symptoms worsen. 

What if the seton falls out?

If your seton falls out or breaks: 

• Do not try to replace it yourself  
• Contact your surgical team for advice  

Urgent help is needed if you develop severe pain or fever. 

When is the seton removed?

This varies depending on your condition. 

It may be: 

• Left in place long-term  
• Removed once inflammation settles  
• Replaced during further treatment  

Your surgeon will decide the best plan for you. 

What should I expect during recovery?

Most people recover quickly and can: 

• Walk normally the next day  
• Return to light activities within a few days  
• Return to work within a few days to a week  

Avoid heavy lifting or strenuous activity for 1–2 weeks. 

How can I care for the area?

To stay comfortable and reduce infection risk: 

• Take warm baths (sitz baths) for 10–15 minutes  
• Keep the area clean and dry  
• Use soft gauze or pads to absorb discharge  
• Apply barrier cream if the skin becomes irritated  
• Eat a high-fibre diet and drink plenty of fluids  
• Wear loose, comfortable clothing  

Can I continue normal activities?

Yes. You can usually: 

• Shower or bathe normally  
• Continue daily activities  
• Resume work when comfortable  

You may also continue sexual activity, but you may prefer gentle approaches and good communication with your partner. 

When should I seek medical help?

Seek medical advice urgently if you develop: 

• Increasing pain not relieved by medication  
• Fever or chills  
• Heavy bleeding  
• Signs of infection (redness, swelling, warmth)  
• New or worsening symptoms  

You can contact your GP, NHS 111, or urgent care services if needed. 

Who should I contact if I have concerns?

Important

Even with treatment, fistulas can sometimes recur. Early recognition of symptoms and ongoing care are important for good outcomes. 

This leaflet provides general guidance and does not replace advice from your healthcare team.