Crohn’s disease causes anal fissures through several overlapping mechanisms: chronic inflammation that damages the anal lining, frequent diarrhea that breaks down skin, reduced blood flow that prevents healing, and increased pressure from the anal sphincter muscle. Anal problems affect anywhere from 20 to 80 percent of people with Crohn’s, and fissures are among the most common. Understanding how these tears form helps explain why they behave differently from ordinary fissures and why they can be harder to treat.
Inflammation Weakens the Anal Lining
The most fundamental driver is the chronic, destructive inflammation that defines Crohn’s disease. Crohn’s doesn’t just irritate the surface of the gut. It penetrates through multiple layers of tissue, weakening the structural integrity of the lining from the inside out. In the anal canal, this means the thin, delicate skin (called the anoderm) becomes fragile and prone to splitting.
On a microscopic level, the inflammation creates defects in the protective barrier of cells that normally keeps the anal canal intact. Once that barrier breaks down, bacteria and other irritants from stool can invade deeper tissue layers, triggering more inflammation and making the original tear worse. This creates a cycle: inflammation causes a crack, the crack lets in more irritants, and those irritants fuel more inflammation. In ordinary fissures, the initial tear is usually mechanical, caused by passing a hard stool. In Crohn’s, the tissue is already compromised before any mechanical stress occurs.
Chronic Diarrhea Erodes the Skin
People with Crohn’s often experience frequent, loose bowel movements. While most people associate fissures with constipation, diarrhea is just as capable of causing them, and through a different mechanism. Repeated exposure to liquid stool dries out and macerates the skin of the anal canal, much the way repeatedly washing dishes without gloves causes the skin on your hands to crack and split. The digestive enzymes still present in loose stool add a chemical irritation on top of the physical one.
The sheer frequency of bowel movements matters too. Every trip to the bathroom stretches the anal canal, and when you’re going six, eight, or more times a day, the tissue never gets a break. Skin that’s already weakened by Crohn’s inflammation has even less capacity to tolerate this kind of repeated stress.
Reduced Blood Flow Prevents Healing
Even in people without Crohn’s, the back wall of the anal canal (the posterior midline) has a naturally weaker blood supply than the rest of the canal. That’s why about 90 percent of ordinary fissures occur there. Healing requires good blood flow to deliver oxygen and repair cells to the damaged tissue, and this area is already at a disadvantage.
Crohn’s disease makes this problem worse. The microvascular changes associated with Crohn’s inflammation further reduce blood flow to the anal lining. Think of it as trying to heal a cut on your skin while wearing a tourniquet. The raw materials for repair simply can’t reach the wound efficiently. This is a key reason why Crohn’s fissures so often become chronic rather than healing on their own within a few weeks the way most ordinary fissures do.
Sphincter Pressure Chokes Off Circulation
Research has found that people with Crohn’s disease have higher resting pressure in their anal sphincter muscle compared to healthy controls, even when they don’t have visible inflammation in the rectum. This elevated pressure matters because the resting tone of the internal sphincter is already high enough in healthy people (around 80 to 100 mmHg) to nearly match the pressure inside the small arteries that feed the anal canal.
When that resting pressure climbs even higher, it essentially squeezes the blood supply shut. The sphincter goes into a sustained spasm around the fissure, further reducing circulation to the wound. This is the same vicious cycle seen in ordinary chronic fissures: pain from the tear triggers spasm, spasm reduces blood flow, reduced blood flow prevents healing, and the unhealed tear continues to cause pain. In Crohn’s patients, the baseline pressure is already elevated before the fissure even forms, so the cycle kicks in faster and is harder to break.
How Crohn’s Fissures Look Different
Ordinary anal fissures are typically a clean, narrow tear sitting in either the back or front midline of the anal canal. Crohn’s fissures often look and behave differently. The classic teaching is that a fissure located off the midline (to the side) should raise suspicion for Crohn’s disease. These atypical fissures tend to have a granulating base, meaning the wound bed looks raw and bumpy rather than clean. The edges may overhang the wound, and the fissure can extend beyond the anal canal onto the surrounding perianal skin. Multiple fissures may be present at the same time.
That said, most fissures in Crohn’s patients (about 66 percent) still occur in the posterior midline, and 84 percent present with the classic symptoms of pain and bleeding during bowel movements. So a “normal-looking” fissure doesn’t rule out Crohn’s, and an atypical one doesn’t confirm it on its own. Crohn’s fissures are also commonly accompanied by large, swollen skin tags sometimes called “elephant ears,” which are broad-based, edematous tags that may appear cyanotic (bluish) and can be tender to the touch.
The Risk of Progression to Fistulas
One of the more serious concerns with Crohn’s fissures is their potential to deepen and evolve into fistulas, which are abnormal tunnels connecting the anal canal to the surrounding skin or other organs. The mechanism starts with a fissure that doesn’t heal. As the tear deepens through the layers of the anal wall, it can penetrate into the tissue beyond the canal. The outer part of the fissure may partially heal over, creating a skin bridge that traps stool and bacteria underneath. This leads to infection, further tissue destruction, and eventually the formation of a tube-like tract.
On a cellular level, Crohn’s inflammation drives a process where the cells lining the gut transform into a more mobile, invasive cell type. These transformed cells can burrow into deeper tissue layers, causing localized damage and helping form the tunnel structure of a fistula. This is why controlling Crohn’s inflammation is considered essential to preventing fissures from progressing. An unhealed fissure that lingers for months is not just a pain management problem; it’s a potential starting point for more complex perianal disease.
Treatment Differs From Ordinary Fissures
For most people without Crohn’s, a chronic fissure that doesn’t respond to warm baths and stool softeners is treated with a minor surgical procedure that cuts a small portion of the internal sphincter to release the spasm and restore blood flow. This approach has historically been considered risky in Crohn’s patients because of concerns about poor wound healing and the potential for incontinence in tissue already compromised by inflammation.
However, the picture is more nuanced than a blanket “no surgery” rule. In one study of Crohn’s patients with fissures, 67 percent of those treated surgically healed. Among patients who specifically underwent local procedures on the anal canal, the healing rate reached 88 percent, compared to just 43 percent for those who had surgery only on the intestine further upstream. The same study documented that unhealed fissures frequently progressed to more serious anal disease over time, suggesting that carefully selected surgical treatment may be safer than leaving a stubborn fissure alone.
The first-line approach for Crohn’s fissures is still medical: controlling the underlying intestinal inflammation, managing diarrhea, and using topical treatments to relax the sphincter and improve local blood flow. Surgery is reserved for fissures that fail to respond, but it remains a viable option when the surrounding tissue is in reasonable condition and the disease is not actively flaring.