Two conditions, side by side.
Anal fissures and anal fistulas are often spoken about in the same breath, but they are different problems with different causes and different treatments. Understanding which is which is the first step in choosing the right path.
Anal fissure
A small split or tear in the thin lining (anoderm) of the anal canal — most often along the back midline. Most fissures are caused by passing a hard or large stool, or by repeated diarrhoea, that stretches and tears the delicate tissue.
How it feels
- Sharp, knife-like pain during a bowel movement
- Pain that lingers for minutes to hours afterwards
- Bright red blood on the toilet paper or stool surface
- A visible crack or skin tag near the anus
- Spasm of the internal sphincter — a tight, throbbing ache
Acute vs chronic
An acute fissure heals within about six weeks with conservative care. A chronic fissure is one that has not healed in that window — often kept open by ongoing sphincter spasm reducing blood flow to the area.
Anal fistula
An abnormal, narrow tunnel that connects the inside of the anal canal to the skin around the anus. Most fistulas begin as an infection in one of the small anal glands, which becomes an abscess. When the abscess drains — surgically or on its own — the tract that remains is a fistula.
How it feels
- A small opening on the skin near the anus that drains pus, blood, or stool
- Persistent throbbing pain that can flare unpredictably
- Recurrent abscesses in the same spot
- Skin irritation, itching, or unpleasant odour from drainage
- Fevers or chills if an abscess is forming
Why it persists
Fistulas rarely heal without surgery. The tract becomes lined with scar tissue and stays connected to bacteria-rich gut contents, so infection keeps cycling. Surgery is almost always required to close it definitively.
What sets these conditions in motion.
Common triggers for fissures
- Constipation and passing hard stools — the leading cause.
- Chronic diarrhoea, which irritates and softens the lining.
- Childbirth, especially after vaginal delivery.
- Inflammatory bowel disease (Crohn's disease in particular).
- Prolonged straining on the toilet, including from low-fibre diets.
- Anal intercourse without sufficient lubrication or care.
Common triggers for fistulas
- Untreated or recurrent perianal abscesses — by far the most common cause.
- Crohn's disease, which can produce complex fistulas as part of its disease process.
- Tuberculosis and certain chronic infections in some regions.
- Trauma or surgery in the anorectal area.
- Radiation therapy for pelvic cancers.
- Diverticulitis or other deep infections that track outward.
Where the two conditions overlap
A long-standing chronic fissure can sometimes become infected and tunnel inward, evolving into a fistula. The fissure is the tear; the fistula is the tunnel that forms when infection takes hold. This is why early treatment of a fissure matters — not just for comfort, but to prevent the more complex condition that can follow.
Don't wait this one out.
Many people delay seeking help because the topic feels embarrassing or because they hope the symptoms will resolve. Some do — most acute fissures heal with simple measures. But certain signs deserve prompt evaluation:
Seek care promptly if you have:
- Pain or symptoms persisting beyond a couple of weeks
- A lump, swelling, or area of redness near the anus (possible abscess)
- Fever, chills, or feeling generally unwell with anal pain
- Persistent drainage of pus or blood
- Bleeding that is heavy, dark, or accompanied by changes in bowel habit
- Symptoms after radiation, with Crohn's disease, or with reduced immunity
A clinician — typically a GP first, then a colorectal specialist if needed — can usually make the diagnosis from a careful history and a brief examination. Imaging (such as an MRI) may be added for fistulas to map the tract before surgery.