An anal fissure is a small tear in the lining of your anal canal — the short passage that stool travels through on the way out. It almost always happens in the same spot: the back of the canal (the 6 o'clock position if you imagine a clock face). That particular spot heals slowly because it gets slightly less blood flow than everywhere else.
Even though the tear is tiny — often just a few millimetres — it hurts more than you'd expect. That's because the anal canal has a dense network of pain nerve fibres. Think of it like a paper cut on your fingertip: small, but surprisingly painful. The difference is that every time you have a bowel motion, the stool passes right through it.
When your stool is hard, dry, and large, your body has to stretch the anal canal further than it's designed to go. If the stool is too firm or you're straining too hard, the lining tears — and there's your fissure.
The back of the canal is the weakest spot because the surrounding muscle gives it less support there, and the blood supply is already a little reduced. So when something has to give, that's where it happens.
The important thing to understand is that as long as your stools remain hard, every bowel motion re-injures the tear. That's why softening your stool isn't just one option among many — it's the foundation that everything else is built on. A fissure simply cannot heal if it's being torn open again each day.
It helps to see the whole picture, because this is why fissures can drag on for so long:
- Constipation → hard stool → fissure tear
- Fissure → severe pain → the sphincter muscle goes into spasm
- Pain + muscle spasm → you avoid going to the toilet
- Avoidance → stool builds up and becomes larger and harder
- Harder stool → the fissure is torn again with the next motion
- Each cycle makes the next one worse
To heal, you need to tackle both sides at once — soften the stool so each bowel motion causes less damage, and relax the muscle spasm so the wound can actually close. Doing one without the other rarely works.
- Pain so bad you can't have a bowel motion for more than 2 days — the stool can become impacted (stuck), which needs medical help
- Blood mixed through the stool (not just on the paper) alongside constipation — worth getting checked to be sure nothing else is going on
- Constipation with unexplained weight loss, abdominal pain, or a change in how your stools look — please see your GP
- Your fissure isn't getting better after 6–8 weeks of consistent treatment
- Fever or swelling around the anus — this could mean a secondary infection
Stool softening — the most important step
Everything else depends on this. If your stools stay hard, the fissure will keep being re-torn and nothing else will have a chance to work.
- Dietary fibre: Aim for 25–35g per day. Soluble fibre from oats, psyllium, and legumes is particularly helpful — it absorbs water and makes stools softer and easier to pass. A fibre supplement like Metamucil or Benefiber is a simple, reliable way to get there consistently.
- Water: Fibre without enough water can actually make constipation worse. Drink at least 1.5–2 litres of water every day.
- Stool softener medication: Lactulose (15–30ml daily) or macrogol (1–2 sachets of Movicol or Osmolax) draw water into the bowel and gently soften stools. Both are safe for ongoing use and make a real difference to how much each bowel motion hurts while the fissure is healing.
- Don't strain: If the stool isn't moving easily, step away from the toilet and try again a little later. Straining through an already-sore anal canal makes things worse, not better.
Warm sitz baths
Sitting in a bowl or shallow bath of warm water for 15–20 minutes after each bowel motion is one of the simplest and most effective things you can do. The warmth relaxes the sphincter muscle — which is what causes most of that long, aching pain after you go — and eases the pain. It costs nothing and works well.
Topical muscle-relaxant ointments
The standard prescription treatment for a fissure that hasn't healed on its own is a topical ointment that relaxes the sphincter. Diltiazem 2% and nifedipine are calcium-channel-blocker ointments commonly used; glyceryl trinitrate (GTN) 0.2% is an alternative but often causes headaches. You apply a small amount inside and around the anal canal twice a day for 8–12 weeks. The ointment lowers the resting pressure of the sphincter and improves blood flow to the tear — which is exactly what the fissure needs to heal. The full 8–12 weeks is important; stopping when it feels a bit better is the most common reason the fissure comes back.
Botulinum toxin injection (Botox)
If the fissure hasn't healed with cream after a proper course of treatment, a Botox injection into the sphincter muscle is the next step. It temporarily relaxes the muscle for 3–4 months — long enough for most fissures to heal. It's a short procedure and a well-established next step in the conservative treatment ladder.
Lateral internal sphincterotomy (surgery)
When a fissure has resisted both cream and Botox, a small operation called a lateral internal sphincterotomy (LIS) can be done. A very small portion of the sphincter muscle is gently divided, which permanently lowers the pressure and allows healing. In published series, more than 90% of fissures heal with this approach, and pain relief is usually substantial and fast.
A simple daily routine while your fissure heals
- Morning: Take your stool softener (lactulose or macrogol) and your fibre supplement
- Through the day: Drink at least 8 glasses of water
- Twice daily: Apply your prescribed sphincter-relaxant ointment
- After each bowel motion: Sit in a warm sitz bath for 15–20 minutes
- On the toilet: Keep it to 5 minutes; a small footstool under your feet reduces the need to strain
- If the stool won't come: Step away — never strain through a hard stool onto an injured canal
Surgery (lateral internal sphincterotomy) is the right choice when a fissure has been going on for more than 8–10 weeks and hasn't responded to consistent cream use, or when Botox hasn't achieved healing either. For people whose daily life is seriously affected by the pain, surgery offers fast and reliable relief.
One important thing to know: surgery fixes the muscle spasm — but it doesn't fix constipation. If your fissure was caused by constipation, you'll still need to keep up with the dietary and lifestyle changes afterwards to prevent it coming back.
Yes, surprisingly. Repeated loose, urgent stools can also cause a fissure — the frequent irritation to the anal canal and the acidity of liquid stool can both cause or worsen a tear. Fissures from diarrhoea tend to occur in a slightly different position and may come with perianal skin irritation.
Possibly, yes. Iron supplements are well known for causing constipation and producing hard, dark stools. If you developed anal pain shortly after starting iron tablets, there's likely a direct connection. Talk to your GP about whether a gentler iron preparation might work for you, and ask about starting a stool softener at the same time.
The types used here — osmotic laxatives like lactulose and macrogol (Movicol/Osmolax) — are safe for long-term use and are not habit-forming. They're appropriate to take for weeks to months while your fissure heals, and during any period when constipation is more likely (illness, travel, less activity, certain medications).
Yes — constipation is the most common cause of fissures in children too. Treatment focuses on softening the stool (dietary changes, lactulose), warm baths, and making toilet time calm and unhurried. Children usually get better quickly with these measures. Topical creams can be used in older children under medical guidance.
If it's a recent fissure — possibly, yes. Softening the stool alone heals roughly half of new fissures within 4–6 weeks. If your fissure has been going on for a while and has become chronic, softening the stool is essential but usually isn't enough on its own — you'll also need a topical cream or other treatment to address the muscle spasm.
Need a specialist opinion?
If something in this article matches what you're experiencing, the most useful next step is a proper assessment. A GP referral is required.