Anal fistula

Overview

An anal fistula is a small tunnel that forms between the end of the bowel (the anal canal) and the skin near the anus. It usually develops after an infection in the anal glands, which causes an abscess (a pocket of pus). When the abscess drains, it can leave a permanent tunnel behind. This tunnel can cause ongoing drainage of pus or blood, and may be uncomfortable.

Anal fistulas are not extremely common, but they are not rare either. They affect about 1 in 10,000 people each year. Many people who have an anal abscess later develop a fistula.

Anal fistulas can affect anyone, but they are more common in adults between 30 and 50 years old. Men are slightly more likely to get them than women. People with certain conditions, like Crohn's disease, are at higher risk.

Symptoms

Common symptoms

• Pain or discomfort around the anus, especially when sitting or during bowel movements
• A small opening in the skin near the anus that may drain pus, blood, or fluid
• Swelling and redness around the opening
• Irritation or itching in the area
• Fever or feeling unwell if there is an active infection

Symptoms in children

• Similar symptoms as adults, but children may be less able to describe the pain
• Fussiness, crying when having a bowel movement, or holding back from pooping
• Drainage or a lump in the diaper area

Symptoms in older adults

• Symptoms are the same as in younger adults, but older adults may have other health issues that complicate treatment
• Increased risk of infection or delayed healing due to weaker immune systems
• May experience more discomfort with bowel movements if they also have constipation

Causes

Main causes

• An infection in the anal glands that leads to an abscess (a pocket of pus). When the abscess drains, either on its own or with medical help, it can leave a tunnel that becomes a fistula.
• Less common causes include injury to the anal area, radiation therapy for cancer, or conditions that cause inflammation in the bowel, such as Crohn's disease or ulcerative colitis.
• In some cases, the exact cause is unknown.

Risk factors

• Having had an anal abscess that did not heal completely
• Inflammatory bowel disease, such as Crohn's disease or ulcerative colitis
• A weakened immune system, from conditions like HIV, diabetes, or chemotherapy
• Constipation or chronic diarrhea that puts strain on the anal area
• Obesity or a sedentary lifestyle

When to see a doctor

See a doctor urgently if:

• If you have severe pain, high fever, or signs of a serious infection
• If you notice new or worsening drainage of pus or blood
• If the area around the anus becomes very swollen or red

Book a routine appointment if:

• If you have ongoing discomfort or drainage from the anal area for more than a few days
• If you have had an anal abscess before and still have symptoms
• If you have a known condition like Crohn's disease and develop anal symptoms

Diagnosis

A doctor will ask about your symptoms and medical history, and then examine the area around your anus. They may gently insert a gloved finger into the rectum to feel for the fistula tract. This is called a digital rectal exam.

Tests that may be done

• Anoscopy: A small, lighted tube is used to look inside the anal canal.
• Proctoscopy or sigmoidoscopy: A longer scope to examine the lower bowel.
• Imaging tests like an MRI (magnetic resonance imaging) or ultrasound to see the full path of the fistula and rule out deeper infection.
• In some cases, a small amount of dye is injected into the fistula opening to see its path on an X-ray (fistulogram).

What to expect at your appointment

The diagnosis is usually straightforward. The doctor will explain the location and complexity of the fistula. They may refer you to a colorectal surgeon (a specialist in surgery of the bowel and anus). Treatment often involves surgery, but the doctor will discuss all options with you.

Treatment

Treatment for an anal fistula depends on its location, depth, and complexity. The main goal is to remove the fistula while keeping the anal sphincter muscles (the muscles that control bowel movements) intact. Surgery is the most common treatment, but less invasive options may be used for simple fistulas.

Self-care at home

• Keep the area clean: Gently wash with warm water after bowel movements and pat dry.
• Take warm baths (sitz baths) for 10-15 minutes several times a day to relieve discomfort and help drainage.
• Use a soft, clean pad or gauze to absorb any drainage.
• Avoid straining during bowel movements – drink plenty of water and eat a high-fiber diet.
• Do not use creams or ointments without asking your doctor, as some may irritate the area.

Medical treatments

Your doctor may prescribe antibiotics if there is an active infection. However, antibiotics alone cannot cure a fistula – they only treat infection. Other treatments include seton placement (a thin thread left in the fistula to help it drain and heal), fibrin glue (a substance that seals the tunnel), or laser treatment. The best option depends on your specific case.

When is surgery considered?

Most anal fistulas require surgery to remove the tunnel and prevent it from coming back. The most common procedure is a fistulotomy, where the surgeon opens the fistula and lets it heal from the inside out. For more complex fistulas, other techniques may be used to protect the anal muscles. Surgery is usually done as a day case or with a short hospital stay.

Living with this condition

Living with an anal fistula can be uncomfortable, but most people manage well with good hygiene and care. After surgery, there will be some discomfort and drainage for a few weeks. You will need to take time off work and avoid heavy lifting or strenuous activity. Your doctor will tell you when you can return to normal activities.

Lifestyle tips

• Eat a high-fiber diet (fruits, vegetables, whole grains) to keep stools soft and reduce straining.
• Drink plenty of water – at least 8 glasses a day.
• Avoid sitting for long periods – get up and walk around every hour.
• Use a cushion with a hole (called a donut cushion) if sitting is painful.
• Practice good anal hygiene: wash gently, pat dry, and change pads regularly.

Diet and exercise

A diet rich in fiber and plenty of fluids helps prevent constipation. Gentle exercise, like walking, is fine, but avoid heavy lifting or cycling until your doctor says it is safe. After surgery, follow your doctor's advice on activity levels.

Mental health and emotional wellbeing

Dealing with an anal fistula can be embarrassing or stressful. It is normal to feel anxious or frustrated. Talk to your doctor or a counsellor if you feel overwhelmed. Remember that this is a common medical problem, and treatment is very effective.

Prevention

There is no sure way to prevent an anal fistula, but you can reduce your risk by treating anal abscesses promptly and completely. Keeping the anal area clean and avoiding constipation or chronic diarrhea may help. If you have Crohn's disease, managing your condition with your doctor's help can lower the risk of fistulas.

Complications

If left untreated

• Recurring infections and abscesses, which can cause more pain and tissue damage.
• Spread of infection to deeper tissues, leading to a serious condition called sepsis (infection in the blood).
• Formation of a more complex fistula that is harder to treat.
• Incontinence (loss of bowel control) if the fistula damages the anal sphincter muscles over time.

Long-term outlook

With proper treatment, most anal fistulas heal completely and do not come back. Surgery has a high success rate, especially for simple fistulas. Even complex fistulas can be treated effectively, though they may require more than one procedure. Most people return to their normal lives without lasting problems. Your doctor will guide you through the best option for your situation.

Find support

Local organisations

• Crohn's & Colitis UK · United Kingdom
• NHS – Anal fistula information · United Kingdom

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