A perianal fistula usually feels like a sore, tender spot beside the anus that aches or throbs, builds pressure over days, then eases when pus, blood or watery fluid leaks out of a small opening in the skin. The leak leaves a wet, itchy, irritated patch and stained underwear, and sitting, walking and bowel movements tend to make the soreness worse. Then the opening crusts over and the cycle can start again.
That is the typical pattern, and it is the one most pages describe. What they rarely say is the part that matters most if you have Crohn's disease: some fistulas cause almost nothing until they block and an abscess forms, and nearly half of fistulas in one population study turned up before or at the moment Crohn's was diagnosed (Schwartz 2002). So this guide covers what a fistula feels like, how that differs from a fissure, a hemorrhoid or an abscess, what drainage is and is not normal, why your Crohn's score can look fine while your fistula is not, and when to get seen the same day.
What does a perianal fistula feel like?
A perianal fistula typically feels like soreness or a dull, sometimes throbbing ache beside the anus, with a small spot that leaks pus, blood or fluid. Pain often builds when the opening blocks and eases once it drains. Many people also describe itching, a constantly damp feeling and irritated skin. The sensations vary a lot with how deep and how inflamed the tract is.
A fistula is a tunnel. In the anus it runs from an opening inside the anal canal to a second opening on the skin nearby, usually somewhere around the buttock or the area between the anus and the genitals (Gaertner 2022). What you feel depends on what that tunnel is doing at the time.
The best description of the experience comes from a UK qualitative study in which twelve people with Crohn's perianal fistulas were interviewed at length. Pain and discharge were described by every participant. Pain was usually worst when the fistula was first diagnosed, when an abscess developed, or when the fistula flared, and it was described as intense or sharp. Several people also described a background of discomfort simply from the fistula being there, with one participant saying they had not had a pain-free day in nearly four years (Adegbola 2020). Several of the authors reported advisory or speaking fees from companies that make IBD treatments; the paper's findings are interview themes rather than a treatment claim, but the disclosure is worth knowing.
In Crohn's communities, people describe the same thing in plainer words. In one r/CrohnsDisease thread asking whether anyone can tell a fistula from a fissure or abscess by feel, people with long experience described a fistula as a deep, dull ache, sometimes a pulsing or shooting pain, that mostly announced itself when something passed through it or when it blocked, at which point pus or blood appeared and pressing nearby gave a little relief. Others said they could feel watery stool or gas going through the tract. Those are personal accounts rather than evidence, but they match the clinical pattern closely.
The pressure-drain-relief cycle
If there is one sensation that marks out a fistula, it is the cycle. The tract fills, the outside opening crusts or narrows, pressure and tenderness build, and the area may swell and feel hot. Then it opens, drains, and the pain drops noticeably. A surgical guideline puts it simply: people with an anal fistula typically report intermittent swelling and drainage (Gaertner 2022).
The practical point is that a fistula that has stopped draining is not necessarily getting better. If drainage stops and pain, swelling and throbbing climb over a day or two, the more likely explanation is that an abscess is forming behind a blocked opening.
Is a perianal fistula painful all the time, or only when sitting?
Most people describe pain that changes with position and activity rather than a constant level. Sitting, walking, driving over bumps and bowel movements commonly make it worse. Between flares, many people feel only soreness or nothing much. Deep abscesses can send pain into the perineum, lower back or buttocks rather than staying beside the anus.
In the UK interviews, sitting, certain stances, walking and running all brought on pain or irritation. One participant could not sit for more than fifteen minutes; others described learning to walk, sit and stand differently, limping, and finding speed bumps difficult when driving (Adegbola 2020). Pads and gauze used to catch leakage added their own rubbing and irritation.
Where the pain is felt also varies. Superficial abscesses usually cause obvious pain and swelling near the anus, while deeper ones, higher up in the pelvis, may present with pain referred to the perineum, lower back or buttocks, and the outside of the area can look surprisingly normal (Gaertner 2022). That is why "it hurts but I cannot see anything" is not reassurance on its own.
Pain also matters most to people living with it. In a survey of 69 people with perianal Crohn's disease, anal pain or discomfort was rated the single most important quality-of-life factor, rated highly important by 40% of respondents (Mahadev 2011). If you want help putting the sensation into words a clinician will use, our guide to describing pain to a doctor covers pain vocabulary and scales.
What does fistula drainage look and feel like?
Fistula drainage is fluid leaking from the skin opening beside the anus. It may be pus (cloudy, yellow or green), blood-stained, watery, or contain mucus or traces of stool. It usually feels like a wet patch rather than a leak you can control, and it can irritate the skin, stain clothes and smell. A sudden change in amount, colour or smell is worth reporting.
Every participant in the UK study described the burden of discharge, whether they called it leakage, seepage or discharge. People worried about odour, visible staining, damage to the skin around the anus, and the need for barrier protection, and those with setons (soft surgical threads placed to keep a tract draining) described persistent discharge that felt like incontinence (Adegbola 2020). In one r/CrohnsDisease thread, people swapped tips on period pads for keeping drainage off clothes at work, and in another, people with rectovaginal fistulas described going through a lot of gauze.
Some drainage is expected with a known fistula, particularly one held open with a seton. What changes the picture:
- Drainage stops and pain climbs. This is the blocked-abscess pattern described above.
- New or stronger smell with more pain, redness or fever. This can mean infection is building.
- Stool or gas coming through the vagina. This suggests a rectovaginal fistula and needs assessment.
- A lot of fresh blood. Small amounts of blood-stained fluid are common; heavier bleeding is not something to sit on.
Does a fistula look like a pimple?
The outside opening often looks like a small red spot, bump or pimple near the anus that opens, leaks, crusts over and reappears in the same place. Some openings are hard to see at all. Because a fistula is a tunnel rather than a surface spot, squeezing it does not empty it, and the opening closing over does not mean the tract has healed.
When a clinician examines the area, they look for this external opening, signs of an abscess, scars and signs of Crohn's disease around the anus, and may gently probe the opening if it is tolerated (Gaertner 2022).
The trap is the opening that closes. One MRI study followed 18 people with Crohn's perianal fistulas through treatment. Active, inflamed tracts persisted on MRI in 8 of 11 people whose fistulas had clinically responded, and the authors concluded that tracts can persist with residual inflammation despite closure of the outside openings, which may cause recurrent fistulas and abscesses (Van Assche 2003). A larger follow-up from the same centre, 59 people, found that MRI improvement lined up with clinical improvement in only about half of patients (Karmiris 2011). In a landmark drug trial, fistulas that closed stayed closed for a median of three months (Present 1999). We could not read a funding or conflict statement for that trial.
So if your opening has closed but you still feel deep aching or pressure, that is worth telling your team. The surface is not the whole story.
Fistula, abscess, fissure or hemorrhoid: how do they feel different?
A fissure causes sharp, tearing pain during and after a bowel movement. Internal hemorrhoids classically bleed without pain. A thrombosed external hemorrhoid is a painful lump at the anal edge. An abscess is a hot, swollen, increasingly painful lump that may bring fever. A fistula causes recurring swelling and drainage from an opening beside the anus.
These overlap, they can coexist, and in Crohn's disease they often do. Treat this table as a way to describe what you feel, not a way to diagnose yourself.
| How it typically feels | What you might see | Typical timing | |
|---|---|---|---|
| Anal fissure | Sharp, tearing pain, often described as passing glass, during a bowel movement and for hours after | A little bright red blood on paper | Tied to each bowel movement |
| Internal hemorrhoid | Often painless; may feel like tissue protruding | Bright red blood with bowel movements | Comes and goes with straining |
| Thrombosed external hemorrhoid | A painful lump at the anal edge that cannot be pushed back in | A lump at the anal edge | Comes on suddenly |
| Perianal abscess | Throbbing, building pain and swelling; hard to sit; may feel feverish or unwell | Red, hot, tender swelling | Worsens over days |
| Perianal fistula | Soreness or dull ache, pressure that eases on draining, itching, wetness | A small opening beside the anus leaking pus, blood or fluid | Recurs in cycles |
The fissure row comes from the colorectal surgeons' fissure guideline, which describes pain provoked by defecation that can last hours and feel like tearing or passing glass. It also says fissures sit at the back midline in 73% of cases, and that fissures to the side, or several fissures, are atypical and call for a fuller evaluation because of links with conditions including Crohn's disease, HIV, syphilis and tuberculosis (Davids 2023). The hemorrhoid rows come from the matching hemorrhoid guideline, which names painless bleeding as the cardinal sign of internal hemorrhoids and warns that rectal bleeding should not automatically be attributed to hemorrhoids (Hawkins 2024). The abscess and fistula rows come from the abscess and fistula guideline, which also lists pilonidal disease, hidradenitis, sexually transmitted infections and anorectal tumours among the look-alikes (Gaertner 2022).
The question "is this a hemorrhoid?" comes up constantly. In one r/CrohnsDisease thread, someone described a large, painful "hemorrhoid" that over-the-counter treatment had not touched, and a reply described the same thing turning out to be an abscess, with a pressure-type pain rather than an itchy one. In another, someone with a deep perianal abscess first noticed only slight pain on sitting, assumed a hemorrhoid, and was in surgery within days. The useful rule: a "hemorrhoid" that is getting more painful, more swollen, or is draining pus is not behaving like a hemorrhoid.
Can you have a perianal fistula with no symptoms?
Yes. Some perianal fistulas cause little or nothing until a tract blocks or an abscess forms, and some are first found on a scan done for another reason. People in Crohn's communities describe discovering complex networks of tracts with no warning. We found no reliable population figure for how often fistulas are silent.
The most-viewed post in the threads behind this guide was a photo pair from someone who discovered a network of perianal fistulas with, in their words, no alarming symptoms beforehand. A reply in the r/CrohnsDisease "what does an anal fistula feel like" thread described one tract that started as a small sharp pain and a lump, and a later one 11 cm long with no lump at all, only severe pain. Experiences span the whole range.
What the research does show is that fistulas often appear early. In the Olmsted County, Minnesota population study, 59 people with Crohn's disease developed at least one fistula, and 26 of them developed it before or at the time of formal diagnosis (Schwartz 2002). People in Crohn's communities often describe exactly this: an abscess or fistula as the first sign, sometimes with no gut symptoms at all, as in this thread on perianal symptoms only. Improving timely diagnosis of perianal Crohn's was one of the top ten research priorities chosen by patients and clinicians in a 2026 global priority-setting exercise (Pelly 2026).
How common are perianal fistulas in Crohn's disease?
In population studies, roughly one in five people with Crohn's develops a perianal fistula. In Olmsted County, the risk was 21% by 10 years and 26% by 20 years after diagnosis. Figures from specialist centres are much higher, because they see the most complicated cases. Anal fistulas without Crohn's are uncommon in the general population.
The figure depends heavily on who was counted:
- Population cohorts. In Olmsted County, 33 of the people studied (20%) developed perianal fistulas, with cumulative perianal risk of 21% at 10 years and 26% at 20 years (Schwartz 2002). A population cohort of 1,162 people in South Limburg found a 5-year perianal fistula rate between about 10% and 14% depending on the era of diagnosis, with no significant change over two decades; colonic disease raised the risk and older age lowered it (Göttgens 2017).
- Guideline summary. The colorectal surgeons' guideline gives 10% to 20% in population-based studies, 50% in longitudinal studies, and nearly 80% among people cared for at tertiary referral centres (Gaertner 2022).
- An older clinic estimate. The paper that introduced the Perianal Disease Activity Index put troublesome perianal disease at about 35% of people with Crohn's (Irvine 1995).
For context, anal fistulas in the general population are uncommon: hospital data from four European countries gave between 1.04 and 2.32 new cases per 10,000 people per year (Zanotti 2007). In people without Crohn's, most anal fistulas start as an infected gland inside the anus (Gaertner 2022). The US National Institute of Diabetes and Digestive and Kidney Diseases fistula page gives the same picture.
Why does Crohn's disease cause perianal fistulas?
In Crohn's disease, perianal fistulas seem to come from inflammation that burrows through the bowel wall rather than from an infected anal gland. Inflammatory signals trigger tissue remodelling that lets a tract form and then keep it open. That is why Crohn's fistulas tend to be more complex, recur more, and need both medical and surgical input.
The surgical guideline makes the distinction directly: in Crohn's disease, anal abscesses and fistulas seem to result from penetrating inflammation rather than infection of an anal gland (Gaertner 2022). A review of the biology describes increased production of signalling molecules including TNF, TGF-beta and IL-13 in the inflamed tissue, which drive a change in the lining cells and an increase in tissue-digesting enzymes, remodelling the tissue into a tract (Panés 2017).
This has a felt consequence. A Crohn's fistula is part of active disease, not just a local wound, so what is happening in the rectum matters. An international consensus states that draining infection always comes first, that healing the rectal lining is the goal when the rectum is inflamed, and that definitive surgical repair is only considered when there is no inflammation in the bowel (Gecse 2014). If your fistula seems to worsen whenever the rest of your Crohn's flares, that fits the biology. Our guide to telling whether you are in a Crohn's flare covers the luminal side.
You may also hear surgeons classify fistulas by how they cross the anal sphincter muscles: intersphincteric, transsphincteric, suprasphincteric and extrasphincteric. That system dates from an analysis of 400 cases in 1976 (Parks 1976). The guideline counts any fistula linked to IBD as complex, along with horseshoe, branching and recurrent fistulas and those crossing a large part of the sphincter (Gaertner 2022).
What does a rectovaginal fistula feel like?
A rectovaginal fistula connects the rectum or anal canal to the vagina. The defining symptom is gas or stool passing through the vagina, which people often notice as unexplained vaginal wind, discharge or soiling. It is less common than other perianal fistulas in Crohn's disease, and it needs specialist assessment.
People who have one often describe the moment of realisation as confusing before it is frightening. In one r/CrohnsDisease thread about rectovaginal fistula, the poster described noticing stool from an unexpected place and passing a lot of air vaginally before realising what was happening, then constant worry about drainage and irritation from pads worn around the clock.
In the South Limburg population cohort, the 5-year rate of rectovaginal fistula fell from 5.7% among people diagnosed between 1991 and 2005 to 1.7% among those diagnosed from 2006 to 2011 (Göttgens 2017). The surgical guideline notes that the cause matters, including obstetric injury, Crohn's disease, gland infection and cancer, and that examination under anaesthesia and imaging are often needed to map the tract (Gaertner 2022). Pain with sex was also a recurring theme for fistulas in general in the UK interviews (Adegbola 2020), and impact on sexual function and intimacy made the global research top ten (Pelly 2026). It is a legitimate thing to raise with your team.
Why can your Crohn's score look fine while your fistula is not?
Standard Crohn's activity scores were built around the gut, not the anus. The Harvey-Bradshaw Index gives a new fistula one point, the same as joint pain, and in the study that created a perianal-specific score, the usual Crohn's indices barely tracked perianal disease at all. A low score can sit alongside a painful, draining fistula.
This is the part most fistula pages miss, and it explains a frustration many people describe: "my numbers are good, so why does it still hurt to sit?" When the Perianal Disease Activity Index was developed in 37 patients over 124 visits, it correlated strongly with both doctors' and patients' global assessments, while the Crohn's Disease Activity Index and the Harvey-Bradshaw Index correlated poorly with it, with correlation coefficients below 0.23 (Irvine 1995). The perianal index looks at pain and restriction of activities, restriction of sexual activity, discharge, the type of perianal disease and induration (Adegbola 2020).
People living with fistulas went further: they described burdens no clinical score captured, and that work produced the 28-item Crohn's Anal Fistula Quality of Life scale, built from interviews and data from 211 patients (Adegbola 2021).
If you score yourself with the Harvey-Bradshaw Index, it is worth seeing how little a fistula moves the total. Our guide to Harvey-Bradshaw scores explains each item.
The fix is not to abandon the score, but to log your perianal symptoms separately so they do not disappear inside a reassuring number.
What is an examination under anaesthesia, and why do they want one?
An examination under anaesthesia (EUA) is a procedure in which a colorectal surgeon examines the anus and rectum while you are asleep or numbed, so they can find the internal opening, trace the tracts and drain any abscess without causing you severe pain. It is often combined with an MRI or ultrasound.
The reason is accuracy. In a blinded comparison of 34 patients with suspected Crohn's perianal fistulas, endoscopic ultrasound was accurate in 91%, MRI in 87% and EUA in 91%, and accuracy reached 100% when any two were combined (Schwartz 2001). The international consensus likewise says the highest diagnostic accuracy comes only from combining methods (Gecse 2014). If an MRI of the pelvis is booked, our guide to what to expect during an MR enterography covers what being in the scanner is like.
The threads behind this guide show why the setting matters to people. In a 109-comment r/CrohnsDisease thread, someone described an abscess being drained in an office under local anaesthetic as the most traumatic medical experience of their life, and dozens of replies said theirs had been done in an operating room under sedation or general anaesthetic, with several saying they would ask for that next time. Others, like one person heading in for a fistula EUA wearing a "lucky butt surgery" shirt, described it as routine. It is reasonable to ask in advance how a procedure will be done and what pain control is planned. That is a question, not a demand for a particular treatment.
Clairop logs meals, symptoms and stool in seconds, then looks for the foods your gut reacts to, including reactions that land days later.
Is a perianal fistula serious?
A perianal fistula is rarely immediately dangerous, but it is a significant complication. Fistulas can form abscesses, recur, need repeated procedures, and affect sitting, work, sex and sleep. Anal and fistula-related cancers are more common in people with perianal Crohn's than in other people with IBD, though they remain rare in absolute terms.
In the Olmsted County cohort, 34% of people with a fistula had at least one recurrence, 83% of fistula episodes needed an operation (most of them minor), and 23% of perianal fistula episodes led to a bowel resection (Schwartz 2002). The UK interviews describe the wider weight: losses at work, avoided social events, planning outings around toilets, and pain-related fatigue compounded by painkillers (Adegbola 2020).
On infection, the US National Institute of Diabetes and Digestive and Kidney Diseases says anorectal fistulas cause infections and abscesses but rarely cause severe infection (NIDDK). Rarely is not never, which is why fever and spreading redness are on the urgent list below.
On cancer, the numbers need careful framing. In the French CESAME cohort of 19,486 people with IBD, 2,911 had past or current anal or perianal Crohn's. Among them, the incidence was 0.26 per 1,000 patient-years for anal squamous-cell cancer and 0.38 per 1,000 patient-years for fistula-related adenocarcinoma, compared with an anal cancer rate of 0.08 per 1,000 patient-years in people without perianal lesions (Beaugerie 2018). Combined, that is roughly one anal or fistula cancer per 1,560 patient-years in the perianal group. The relative risk is clearly higher, but the estimate is fragile: it rests on 11 cancers in that subgroup, and the odds ratio for anal cancer had a confidence interval running from 1.18 to 551.51. The honest message is that a long-standing fistula that changes character deserves a fresh look, not that a fistula is likely to become cancer.
When should I see a doctor about a perianal fistula?
See a doctor promptly for any new lump, swelling, pain or discharge near the anus, especially if you have Crohn's disease or a family history of IBD. Get same-day or emergency care for fever or chills, rapidly worsening pain or swelling, being unable to sit or pass urine, spreading redness, or feeling generally unwell.
Fever is worth measuring rather than guessing. Our post on Crohn's night sweats explains why a thermometer reading beats "I felt hot", and why an abscess is one of the causes worth ruling out first.
You can also run your symptoms through our gut red flags checker, which flags the symptoms that mean a call should not wait.
What should I track if I think I have a perianal fistula?
Track the things that change decisions: pain at rest, when sitting and after bowel movements; drainage amount, colour and smell, including how many pads you use; any lump or swelling; temperature; and dates. Note whether drainage has stopped while pain rose. Keep it separate from your gut symptoms so a good Crohn's day does not hide a bad fistula day.
A short log beats a long story. A useful daily line might be:
- Pain: 0 to 10 at rest, sitting, and after your worst bowel movement
- Drainage: none, light, moderate or heavy; colour; smell; pads or dressings changed
- Lump or swelling: present or not, getting bigger or smaller
- Temperature: a number, with the time
- Function: how long you could sit, whether you missed work or sleep
- Seton: any change, discomfort or if it has come out
People in the r/CrohnsDisease sitz bath thread describe the comfort measures they use, but what helps your clinician most is the trend. Two weeks of "drainage light, pain 3" followed by two days of "drainage stopped, pain 7, temperature 38.1" tells a story no adjective can. Our guide to a symptom tracker your doctor will actually read covers how to hand that over, and Clairop can turn your logs into the one-page summary described on how it works.
Myths about perianal fistulas
"It is just a hemorrhoid." Sometimes it is. But the hemorrhoid guideline itself warns against assuming bleeding is from hemorrhoids (Hawkins 2024), and pus, a recurring spot beside the anus, or worsening throbbing pain are not hemorrhoid features.
"The hole closed, so it has healed." MRI shows tracts often remain inflamed after outside openings close (Van Assche 2003).
"If my Crohn's score is low, my fistula is fine." The general Crohn's indices correlate poorly with perianal activity (Irvine 1995).
"Only people with bad diarrhoea get fistulas." Many fistulas appear before or at Crohn's diagnosis (Schwartz 2002), and people describe perianal disease as their only symptom for years.
"A fistula will turn into cancer." The relative risk is raised, but the absolute rate in the largest cohort was well under one case per 1,000 patient-years (Beaugerie 2018).
"It is too embarrassing to describe." Clinicians who manage perianal Crohn's hear these descriptions daily. Wetness, smell, pain with sitting, and gas through the vagina are precise, useful clinical information. If you are not sure what is happening at the other end too, our guide to Crohn's with constipation rather than diarrhoea covers why rectal and perianal disease should be examined rather than guessed at.
The bottom line
A perianal fistula most often feels like soreness and pressure beside the anus that builds and then eases when it drains, with a wet, irritated patch, pain on sitting, and sometimes a smell. It can also be nearly silent until an abscess forms. If you have Crohn's disease, treat any new perianal lump, swelling or discharge as something to show your team, log it separately from your gut symptoms, and get same-day care for fever, rapidly worsening pain or a fistula that has stopped draining while it hurts more.
