In medical terms, a fissure is a groove, crack, or split in body tissue. The word covers two distinct categories: natural fissures that are normal parts of your anatomy (like the deep grooves in your brain that separate its lobes) and pathological fissures, which are painful tears or cracks that develop in skin, mucous membranes, or tooth enamel. The context tells you which meaning applies. A surgeon discussing a lung fissure is talking about normal anatomy; a doctor diagnosing an anal fissure is describing a wound that needs treatment.
Fissures as Normal Anatomy
Your body has fissures by design. These are grooves or dividing lines that separate organs into distinct sections, and they play an important structural role.
The brain is the most dramatic example. The Sylvian fissure, visible on the side of each hemisphere, is the most prominent landmark on the brain’s surface. It separates the frontal and parietal lobes from the temporal lobe and begins forming as early as 12 to 14 weeks of gestation. Beneath the surface, this fissure houses a fluid-filled space containing major blood vessels that supply the brain. Other deep grooves divide the brain’s left and right hemispheres or separate the cerebrum from the cerebellum.
Your lungs have fissures too. These are thin tissue boundaries that divide each lung into lobes: two lobes on the left, three on the right. These divisions allow each lobe to expand and move somewhat independently during breathing. The liver, spinal cord, and other organs have their own named fissures as well. In all these cases, the word simply means a natural groove or division in the tissue.
Anal Fissures
When most people search for “fissure” in a medical context, they’re thinking about anal fissures, which are small tears in the lining of the anal canal. These are one of the most common reasons for rectal pain and are visible as a crack in the skin when the area is gently examined.
The primary cause in adults is passing large, hard stools, though prolonged diarrhea can also trigger them. Reduced blood flow to the area and excess tension in the sphincter muscles both contribute. Anal fissures are also common after childbirth and in people with Crohn’s disease. Symptoms include sharp pain during bowel movements and bright red blood on the stool or toilet paper. These symptoms can appear suddenly or build gradually over time.
Acute vs. Chronic
An acute anal fissure typically heals within six weeks with basic care. The standard first approach is a six-week trial of conservative measures: warm sitz baths, stool softeners, pain relief, and a high-fiber diet. Drinking plenty of water helps keep stools soft and reduces the strain that caused the tear in the first place. The Mayo Clinic recommends 25 to 35 grams of fiber daily to support healing and prevent recurrence.
If a fissure persists beyond six weeks, it’s classified as chronic. These require stronger intervention, typically prescription topical creams that relax the sphincter muscle and improve blood flow to the area. If topical treatments don’t work, injections to temporarily relax the sphincter are a reasonable next step, with healing rates comparable to topical therapies. For fissures that resist all other treatment, a minor surgical procedure has about a 96% success rate, with most patients fully healed within three weeks. The recurrence rate after surgery is roughly 5%, compared to about 25% with nonsurgical approaches.
What Happens if You Ignore One
Left untreated, a fissure can become a recurring problem. The tear causes sphincter spasms, which reduce blood flow to the area, which slows healing, which keeps the tear open. In rare cases, a chronic fissure can become infected and form an abscess. If that abscess drains, it can create a fistula, an abnormal tunnel between the anal canal and the surrounding skin that typically requires surgical repair.
Skin Fissures
Fissures also develop on the skin, most often on the hands, feet, and heels. These are deep cracks that extend through the outer skin layer and can bleed or become painful, especially when the skin flexes.
The underlying problem is moisture loss from the skin’s surface. This is most common in winter and cold, dry climates, when low humidity pulls water from exposed skin. Frequent bathing in hot water, harsh soaps, and degreasing agents strip the skin’s natural oils and accelerate the process. Certain medications, particularly diuretics, worsen skin drying as a side effect. Older adults are more susceptible because their skin produces less oil and sweat naturally.
Less common causes include nutritional deficiencies (particularly zinc and essential fatty acids), underactive thyroid, and radiation exposure. When skin cracking becomes widespread and itchy, it may indicate a form of eczema sometimes called “eczema craquelé,” named for the cracked-porcelain pattern it creates on the skin’s surface.
Dental Fissures
In dentistry, fissures are the narrow grooves on the chewing surfaces of your back teeth. These are natural features of tooth anatomy, but their depth and shape make them especially vulnerable to decay. Food particles and bacteria settle into these grooves, and toothbrush bristles often can’t reach the bottom.
Dental sealants, a thin protective coating painted onto these surfaces, are the standard prevention strategy. They’re most effective when applied soon after adult molars come in: around age 6 for the first molars and around age 12 for the second set. Sealants can also be applied to baby teeth starting at age 2, and adults can receive them as well. The coating fills in the grooves and creates a smooth surface that’s easier to keep clean.
How Doctors Diagnose Fissures
Most pathological fissures are diagnosed visually. An anal fissure is typically spotted during a physical exam, often appearing as a midline crack. If the fissure is unusual in its location or doesn’t respond to treatment, your doctor may use a small scope to examine the anal canal more closely, or order a colonoscopy to rule out underlying conditions like Crohn’s disease or other inflammatory bowel disorders. Skin fissures are similarly diagnosed on sight, sometimes with a biopsy if an underlying condition is suspected. Dental fissures are identified during routine dental exams, often with the help of an explorer tool that catches on rough or soft spots in the enamel.