An anal fissure is a small tear in the thin, delicate lining of the anal canal. It’s one of the most common causes of sharp pain during and after a bowel movement, and it affects people of all ages. Most fissures heal on their own with simple changes to diet and bathroom habits, though some become chronic and need additional treatment.
What Causes an Anal Fissure
The most common trigger is mechanical trauma to the anal lining. Passing large or hard stools, straining during constipation, and prolonged diarrhea can all stretch or tear the tissue. Childbirth and anal intercourse are also frequent causes. In each case, the tissue simply tears under pressure it can’t withstand.
Less often, a fissure develops as a secondary effect of another condition. Crohn’s disease and other inflammatory bowel diseases can weaken the anal lining, making it more vulnerable. Infections like HIV, tuberculosis, and syphilis can also cause fissures, as can anal cancer. These secondary causes are uncommon, but they’re worth noting because fissures caused by an underlying disease tend to behave differently and may not respond to standard treatments.
Most fissures appear at the back (posterior midline) of the anal opening. About 10% of women and 1% of men develop them at the front instead. A fissure that appears off to the side, rather than front or back, is more likely to have an unusual underlying cause.
What It Feels Like
The hallmark symptom is a sharp, cutting pain during a bowel movement that can feel like passing broken glass. This pain often intensifies afterward and may persist for minutes to hours. Many people also notice bright red blood on the toilet paper or in the bowl.
What makes fissures particularly stubborn is a cycle that develops between pain and muscle spasm. The tear triggers the internal sphincter muscle to clamp down, which reduces blood flow to the area. With less blood reaching the wound, healing slows, and the next bowel movement reopens the tear. This pain-spasm-ischemia cycle is the main reason some fissures refuse to heal without intervention.
Acute vs. Chronic Fissures
A fissure is classified as acute if it’s been present for less than eight weeks. Most acute fissures look like a simple, clean tear and heal with conservative care. Once a fissure lasts beyond eight weeks, it’s considered chronic. Chronic fissures often develop visible features like a small skin tag at the outer edge of the tear or thickened, raised borders around the wound. These signs indicate the tissue has been inflamed and re-injured repeatedly.
How Most Fissures Heal
The first goal of treatment is to break the pain-spasm cycle by keeping stools soft and reducing strain. That starts with fiber. Most people need about 25 to 30 grams per day, which is significantly more than the average diet provides. Adding fiber through whole grains, fruits, vegetables, or a supplement, and drinking plenty of water alongside it, makes bowel movements easier to pass without re-tearing the tissue.
Sitz baths are another cornerstone of at-home care. You sit in a few inches of warm water (around 104°F or 40°C) for 15 to 20 minutes, up to three or four times a day. The warmth relaxes the sphincter muscle, improves blood flow to the area, and eases pain. Many people find a sitz bath right after a bowel movement provides the most relief.
For most acute fissures, fiber and sitz baths are enough. You should notice gradual improvement within a few weeks.
Prescription Options for Stubborn Fissures
When a fissure doesn’t respond to conservative care, the next step is a prescription ointment designed to relax the internal sphincter muscle and restore blood flow to the wound. Two topical treatments have strong evidence behind them: diltiazem 2% ointment and glyceryl trinitrate (nitroglycerin) 0.2% ointment. Both are equally effective at healing fissures, but diltiazem has meaningful advantages. It carries a 30% lower recurrence rate and causes 60% fewer headaches, a common and sometimes disruptive side effect of nitroglycerin.
You typically apply these ointments around the anal opening two to three times a day for six to eight weeks. They work by chemically relaxing the tight sphincter, which lets more blood reach the damaged tissue so it can finally heal.
Botulinum Toxin Injections
If topical treatments don’t work, injecting botulinum toxin (Botox) directly into the sphincter muscle is another option. The injection temporarily paralyzes part of the muscle, breaking the spasm cycle for long enough to allow healing. Doses typically range from 20 to 50 units, and studies report healing rates of 41% to 88% at three months. Some newer protocols using higher doses and more injection sites have reported healing rates above 90%. The effect wears off over several months as the muscle gradually regains function.
When Surgery Becomes Necessary
For chronic fissures that fail all other treatments, surgery is highly effective. The standard procedure, called lateral internal sphincterotomy, involves making a small cut in the internal sphincter muscle to permanently reduce its resting tension. This eliminates the spasm that has been starving the wound of blood flow.
The procedure has a 95% success rate in curing chronic fissures. Long-term complications are rare, estimated at less than 5%. The primary concern is minor fecal incontinence, which can mean small amounts of leakage of stool or gas during recovery. For most people this is temporary, though in a small number of cases it can persist longer. Because of this risk, surgery is reserved for fissures that haven’t responded to less invasive approaches.
Why Some People Get Repeated Fissures
Even after a fissure heals, the area remains somewhat vulnerable. The anal lining is thin, and scar tissue from a previous tear is less elastic than the original skin. People who return to low-fiber diets, become constipated again, or deal with recurring diarrhea are at higher risk of developing another fissure in the same spot. Maintaining adequate fiber intake and hydration long-term is the single most effective way to prevent recurrence. Avoiding prolonged straining on the toilet, and not delaying bowel movements when the urge arises, also helps protect the healed tissue.