CONDITIONS

Perianal Abscess & Fistula

Symptoms, causes, treatment and when to seek urgent help

A perianal abscess is a collection of pus (infection) near the anus, often caused by a blocked anal gland. A fistula is an abnormal tunnel between the inside of the anal canal/rectum and the skin near the anus, which may develop after an abscess drains or is treated. These conditions are common, can be painful, and usually require assessment by a clinician — abscesses often need urgent treatment.

Symptoms Abscess vs fistula Diagnosis Treatments Surgery FAQs

What’s the difference between an abscess and a fistula?

Perianal abscess

A pocket of infection (pus) near the anus. It often causes significant pain and swelling. Abscesses usually need prompt medical assessment and often drainage.

Anal fistula

A small tunnel that connects the bowel/anal canal to the skin. It can cause persistent discharge, recurrent abscesses, or intermittent pain and swelling.

Important

An abscess with fever, spreading redness, or severe pain should be treated urgently. Don’t wait for it to “settle” if symptoms are worsening.

Illustration: where abscesses and fistulas occur (simple guide)

Symptoms

Perianal abscess

  • Severe anal/perianal pain (often constant, worse when sitting)
  • Swelling, a tender lump, redness/warmth of the skin
  • Fever, chills or feeling unwell (sometimes)
  • Pus discharge if the abscess bursts or drains

Anal fistula

  • Persistent or intermittent discharge (pus or fluid) near the anus
  • Recurrent painful swelling or repeated abscesses
  • Skin irritation, soreness, or itching around the opening
  • Pain that flares then improves when it drains

Causes and risk factors

Many abscesses begin when an anal gland becomes blocked and infected. A fistula can form if a tract remains after the abscess drains.

  • Blocked anal glands / bacterial infection (most common)
  • Inflammatory bowel disease (especially Crohn’s disease)
  • Previous abscess (increases the chance of a fistula)
  • Diabetes or immune suppression (may increase infection risk)
  • Less commonly: trauma, radiation, or other inflammatory conditions

How are abscesses and fistulas diagnosed?

Diagnosis is based on symptoms and examination. In some cases, further tests are used to map the fistula tract or look for associated conditions.

  • Clinical examination (often enough for an abscess)
  • Examination under anaesthetic (EUA) to assess and treat
  • MRI pelvis or endoanal ultrasound (often used for complex fistulas)
  • Blood tests if infection suspected; tests for IBD if relevant

Treatment

Perianal abscess treatment

Key point: An abscess usually needs prompt drainage. Antibiotics alone often don’t resolve an abscess because pus is trapped.

  • Incision and drainage (often urgent; can be done in hospital)
  • Antibiotics may be added if there is cellulitis (spreading skin infection), fever, or immune compromise
  • Pain relief, warm baths (sitz baths), and wound care advice

Anal fistula treatment

Treatment depends on the fistula’s path and whether it crosses the sphincter muscles (which control continence). The aim is to cure the fistula while protecting continence.

Common approaches
  • Seton (a soft drain/thread left in place to prevent abscess recurrence)
  • Fistulotomy (opening the tract) for suitable simple fistulas
  • Drainage of any associated collections
Sphincter-sparing options
  • Advancement flap
  • LIFT procedure (ligation of intersphincteric tract)
  • Other specialist techniques where appropriate

Your surgeon will recommend options based on anatomy and continence risk.

Aftercare and recovery

  • Keep the area clean and dry; follow wound-care instructions
  • Warm baths can ease discomfort
  • Manage constipation (soft stool reduces pain/strain)
  • Attend follow-up — fistulas may need staged treatment
  • Seek help if worsening pain, fever, spreading redness, or heavy bleeding

When should I seek urgent help?

Urgent assessment is advised if you have:
  • Severe anal/perianal pain with swelling
  • Fever, chills, or you feel very unwell
  • Rapidly spreading redness or warmth
  • Difficulty passing urine, severe constipation, or escalating pain
  • Known Crohn’s disease with new perianal pain/discharge

FAQs

Can an abscess heal on its own?

Occasionally an abscess may burst and drain, which can temporarily ease pain, but infection often persists. Because abscesses can worsen and spread, it’s best to seek medical assessment promptly.

Do antibiotics cure an abscess?

Antibiotics may help if there’s spreading skin infection or fever, but an abscess usually needs drainage because antibiotics don’t penetrate a closed pocket of pus effectively.

Will an abscess always lead to a fistula?

No, but a fistula can develop after an abscess in some people. If you have persistent discharge, recurrent swelling, or repeated abscesses, a fistula should be considered.

Is a fistula an emergency?

A fistula isn’t always an emergency, but recurrent infection or abscess formation can be urgent. Ongoing discharge, pain, or repeated abscesses should be assessed by a colorectal specialist.

Is perianal fistula linked to Crohn’s disease?

Yes, fistulas can be associated with Crohn’s disease. If Crohn’s is suspected, your team may arrange additional tests and combine surgical and medical treatments.

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