Can Constipation Cause an Anal Tear?

If you've been searching this topic, you've probably had a painful experience on the toilet — and you're wondering whether your constipation is to blame. The short answer is yes, it very likely is. Constipation is the most common cause of anal fissures — small tears inside your back passage — and you are far from alone. This is one of the most common problems we see, and most people get better with the right treatment.

What makes constipation and fissures particularly tricky is that they feed each other. Hard stools cause a tear. The tear hurts. The pain makes you dread going to the toilet, so you hold on. Holding on makes the stool even harder. And a harder stool tears the wound again. Without help, this cycle can go on for months. The good news is that once you understand it, you can break it.

What is an anal fissure?

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 far 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 genuinely painful. The difference is that every time you have a bowel motion, the stool passes right through it.

How constipation causes a fissure

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.

Symptoms of a constipation-related anal fissure

• Severe, sharp pain at the moment of going to the toilet — often described as tearing, cutting, or burning
• A lingering ache or cramp lasting 20 minutes to several hours after the bowel motion
• A small streak of bright red blood on the toilet paper or on the surface of the stool
• Dreading the toilet and putting it off — which only makes the constipation worse
• A small lump of skin at the opening of the anus (called a "sentinel pile" or sentinel tag — a harmless fold of skin that builds up at the outer end of a long-standing fissure)
• Symptoms that get worse after a harder stool, and slightly better when stools are softer

The constipation-fissure-avoidance cycle

It helps to see the whole picture, because this is why fissures can drag on for so long:

1. Constipation → hard stool → fissure tear
2. Fissure → severe pain → the sphincter muscle goes into spasm
3. Pain + muscle spasm → you avoid going to the toilet
4. Avoidance → stool builds up and becomes larger and harder
5. Harder stool → the fissure is torn again with the next motion
6. 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.

When to worry

• 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, tummy 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

Treatment options

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 gives you real relief. It costs nothing and works well.

Topical diltiazem 2% cream

This is the standard prescription treatment for a fissure that hasn't healed on its own. You apply a small amount inside and around the anal canal twice a day for 8–12 weeks. Diltiazem (a type of muscle relaxant) 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 with very good results.

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. More than 90% of fissures heal with this approach, and pain relief is usually dramatic and fast.

When surgery is needed

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 that non-surgical options can't always match.

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.

Frequently asked questions