Hemorrhoids can change the shape of your stool, though the effect is usually subtle and temporary. When internal hemorrhoids swell enough to bulge into the anal canal, they physically narrow the space stool passes through, which can produce thinner, flatter, or grooved stools. The change tends to come and go with flare-ups rather than staying permanent, and it is far more common with large or prolapsing internal hemorrhoids than with external ones. That said, stool shape changes have many possible causes, and a shift that persists deserves a closer look.
How Hemorrhoids Narrow the Passageway
Internal hemorrhoids are swollen vascular cushions that sit inside the anal canal, above the point where you can feel them externally. When they enlarge, they take up room in a channel that is already only a few centimeters wide. A single large hemorrhoid or multiple swollen cushions at the classic anatomical positions can compress passing stool from one or more sides, pressing it into a narrower or irregular profile. If the hemorrhoids prolapse, meaning they slide downward during a bowel movement and partially block the opening, the squeezing effect becomes more pronounced.
Research on hemorrhoid patients has found measurable structural changes beyond the hemorrhoids themselves. A study comparing anal sphincter anatomy in hemorrhoid patients against healthy controls found that both internal and external sphincter muscles were thicker in certain quadrants in the patient group. The authors interpreted these thickenings as a consequence of the disease process itself.
1Annals of Medical Research. The association of anal sphincter morphology and somatotype characteristics with the pathogenesis of hemorrhoidal diseaseThicker sphincter muscles around an already narrowed canal mean less room for stool. This is not like a tumor growing into the passageway and creating a fixed obstruction. Instead, the narrowing fluctuates: when hemorrhoids are swollen and irritated, stool gets squeezed more. When inflammation settles, the canal opens up and stool returns to its usual shape. That variability is one of the ways you can distinguish a hemorrhoid-related shape change from something more concerning.
What the Stool Changes Actually Look Like
People with hemorrhoid-related stool shape changes most commonly describe stools that are thinner than usual, sometimes called ribbon-like or pencil-thin. Some notice a groove or indentation running along one side, reflecting where a single hemorrhoid was pressing against the stool as it passed. Others report that stools come out in smaller pieces rather than one continuous shape, because a prolapsing hemorrhoid can partially obstruct the flow and fragment the stool.
A feeling of incomplete evacuation often accompanies these changes. When prolapsing hemorrhoids partially block the outlet, you can feel like there is more stool that will not come out. That sensation can lead to more straining, which in turn can worsen the hemorrhoids and keep the cycle going. The stool shape issue, in other words, is often just one part of a cluster of symptoms that flare up together.
External hemorrhoids, by contrast, sit outside the anal opening and rarely change stool shape in a meaningful way. They cause pain, itching, and sometimes a visible lump near the anus, but because they are positioned after the point where stool is already formed and exiting, they do not compress it the way internal hemorrhoids can.
The Pencil-Thin Stool Worry
If you search for thin stools online, you will quickly encounter alarming warnings about colorectal cancer. The fear is understandable: a growing tumor inside the colon or rectum can narrow the passageway and produce persistently thin stools. But the reality is more nuanced than the scare stories suggest.
A widely cited analysis in the gastroenterology literature argued that decreased stool caliber, on its own, is not a reliable sign of colorectal cancer. The authors pointed out that loose stool from any diarrheal cause naturally comes out thinner, and diarrheal conditions are far more common than cancer. They concluded that in the absence of other warning signs such as rectal bleeding, a change in overall bowel habits, persistent cramps, or unexplained anemia, referring a patient for colonoscopy based solely on thin stool is not warranted.2PubMed. “Low caliber stool” and “pencil thin stool” are not signs of colo-rectal cancer
That does not mean you should ignore persistent changes. The key distinctions between hemorrhoid-related stool thinning and cancer-related narrowing come down to pattern and duration. Hemorrhoid-related changes tend to fluctuate with flare-ups and improve when the hemorrhoids settle down. Cancer-related changes are typically progressive: the stool gets steadily thinner over weeks or months as the tumor grows. If your stool shape has changed and stayed changed for more than a few weeks, or if it comes with bleeding that looks dark rather than bright red, unexplained weight loss, or worsening abdominal pain, those warrant a conversation with your doctor regardless of whether you also have hemorrhoids.
The Constipation Feedback Loop
Hemorrhoids and constipation feed each other in a way that compounds stool shape changes. Hard, bulky stool requires more straining to pass, and straining increases pressure on the hemorrhoidal cushions, making them swell further. The swollen hemorrhoids then narrow the canal, which can make stool back up and harden further, prompting even more straining. Breaking this cycle is often the single most effective thing you can do for both the hemorrhoids and the stool changes they cause.
Fiber supplementation is the front-line treatment, and the evidence is strong. A Cochrane review pooling seven randomized trials found that fiber supplements cut the risk of persistent hemorrhoid symptoms by about half compared to controls. The same analysis found that bleeding, one of the most common hemorrhoid complaints, was also reduced by roughly half in the fiber group.3PubMed Central. Laxatives for the treatment of hemorrhoids
The mechanism is straightforward: softer, bulkier stool passes more easily, requires less straining, and puts less pressure on the anal canal. When the hemorrhoids shrink in response, the channel widens and stool shape normalizes. Adequate water intake matters alongside the fiber, because fiber without enough fluid can actually worsen constipation. Most adults benefit from gradually increasing fiber rather than jumping to a high dose overnight, which can cause gas and bloating that make the experience worse before it gets better.
When Hemorrhoid Treatment Itself Changes Stool Shape
Here is an irony that surprises many people: some hemorrhoid treatments can create stool shape problems of their own. This is not common with conservative measures like fiber or topical treatments, but it can happen after procedures, particularly surgery.
Rubber band ligation, one of the most widely used office-based procedures for internal hemorrhoids, works by cutting off blood supply to the hemorrhoid with a small rubber band, causing the tissue to shrink and fall off. The procedure is effective for symptom control: in one study of patients with third-degree hemorrhoids, about three-quarters had symptomatic improvement including reduced bleeding and mucosal prolapse.4Journal of General Practice and Emergency Medicine of Nepal. Efficacy of rubber band ligation in third degree hemorrhoid Rubber band ligation carries a low risk of significant scarring. The more serious concern arises with surgical hemorrhoidectomy, the operation that removes hemorrhoid tissue directly.
Anal stenosis, a narrowing of the anal opening caused by excessive scar tissue, is a recognized complication of hemorrhoid surgery. It is uncommon, but when it happens, the consequences for stool shape are significant and potentially long-lasting. One review described anal stenosis as a rare but serious complication, with roughly nine out of ten cases caused by overly aggressive hemorrhoidectomy.5PubMed Central. Surgical treatment of anal stenosis A patient with post-surgical anal stenosis may produce persistently thin stools, experience pain during bowel movements, and sometimes need a second surgery to widen the canal.
A case series examining surgical repair of post-hemorrhoidectomy anal stenosis found that corrective surgery was successful in the vast majority of patients, with most healing within a couple of months, though one patient did require reoperation for recurrence.6PubMed Central. Surgical management of anal stenosis following hemorrhoid treatment: a single-center case series In another reported case, a 30-year-old man developed difficulty passing stool with abdominal pain just four weeks after hemorrhoid surgery, requiring an advancement flap procedure to restore normal function.7PubMed Central. House advancement flap anoplasty in anal stenosis post hemorrhoids surgery. A case report
The practical takeaway is that if you have had hemorrhoid surgery and notice your stool is persistently thinner or more difficult to pass in the weeks that follow, this is worth reporting to your surgeon. Mild narrowing from post-operative swelling is expected and temporary, but a progressive change in stool shape weeks after the procedure may indicate developing scar tissue that is easier to address early.
Other Conditions That Mimic or Overlap With Hemorrhoid Effects
Hemorrhoids are extraordinarily common, affecting a large proportion of adults at some point. Because they are so prevalent, they frequently coexist with other conditions that independently affect stool shape, creating diagnostic confusion. A person can have hemorrhoids and a separate condition at the same time, and the hemorrhoids can be blamed for symptoms that actually have a different source.
Irritable bowel syndrome often produces alternating stool patterns, including narrow or ribbon-like stools during periods of spasm. Pelvic floor dysfunction can prevent the anal canal from relaxing properly during defecation, which compresses stool and contributes to a sense of incomplete evacuation. Rectal prolapse, where the rectal lining slides through the anal opening, creates a physical obstruction similar to prolapsing hemorrhoids but requires different treatment. Even something as simple as dietary changes or dehydration can temporarily alter stool consistency and shape in ways that have nothing to do with the anal canal itself.
The Bristol Stool Chart, which categorizes stools into seven types based on shape and consistency, can be a useful reference point. Types 1 and 2 represent hard, lumpy stools associated with constipation. Types 3 and 4 are considered normal. Types 5 through 7 indicate progressively softer and more liquid stools. Hemorrhoid-related narrowing does not change where your stool falls on this scale in terms of consistency; rather, it changes the cross-sectional shape of whatever consistency you are producing. If your stool is thin but also consistently type 6 or 7, the thinness is likely from the loose consistency, not from hemorrhoids compressing it.
Practical Steps When You Notice a Change
If your stool shape has changed and you suspect hemorrhoids are the cause, there are a few things worth doing before you worry yourself into a spiral of anxious late-night internet research.
- Track the pattern: Note whether the shape change comes and goes or is constant. Hemorrhoid-related changes are almost always intermittent, worsening during flare-ups and resolving between them.
- Look at the full picture: Are you also experiencing pain during bowel movements, bright red blood on the toilet paper, a sensation of something protruding during straining, or itching around the anus? These accompanying symptoms point toward hemorrhoids. Dark blood, unexplained weight loss, or progressive worsening over weeks point elsewhere.
- Increase fiber gradually: Adding a fiber supplement or increasing dietary fiber through fruits, vegetables, and whole grains can reduce hemorrhoid symptoms and normalize stool shape within a week or two. If the shape change resolves with better stool consistency, hemorrhoids were likely the culprit.
- Avoid prolonged sitting on the toilet: Reading or scrolling on your phone during bowel movements extends the time you spend straining and bearing down, even if you do not realize it. This is one of the most common and most fixable contributors to hemorrhoid flare-ups.
If stool shape changes persist despite several weeks of increased fiber and adequate hydration, or if they are accompanied by any red-flag symptoms, a visit to your doctor is worthwhile. For most people under 45 with no family history of colorectal cancer and no alarming symptoms, the evaluation can start with a simple physical exam. For those over 45, or anyone with a family history, persistent changes in stool caliber become a more reasonable trigger for colonoscopy, not because thin stool alone is a reliable cancer sign, but because the screening is valuable on its own and the symptom change is a reasonable prompt to get caught up if you are overdue.
Hemorrhoids During Pregnancy
Pregnancy deserves its own mention because it brings together nearly every hemorrhoid risk factor at once: increased pelvic pressure from the growing uterus, hormonal changes that relax blood vessel walls, increased blood volume, and frequent constipation from both hormonal effects and iron supplements. Many pregnant people develop hemorrhoids for the first time during the third trimester or during labor itself.
Stool shape changes during pregnancy can be especially confusing because so many digestive changes are happening simultaneously. Progesterone slows gut motility, which tends to produce harder and sometimes narrower stools even without hemorrhoids in the picture. When hemorrhoids develop on top of that, the combination can make the stool shape changes more noticeable. The good news is that pregnancy-related hemorrhoids typically improve within weeks to months after delivery, as the pelvic pressure resolves and hormone levels return to their baseline. Fiber supplementation during pregnancy is safe and recommended both for hemorrhoid management and general digestive comfort.
If you developed hemorrhoids during pregnancy and notice persistent stool shape changes that do not resolve in the months after delivery, it is worth having them re-evaluated. Occasionally, the hemorrhoids persist longer than expected and benefit from office-based treatment like banding once the postpartum recovery period is complete.
Why the Anal Canal Is More Dynamic Than People Realize
There is a tendency to think of the anal canal as a fixed pipe, so any change in what comes out must mean something is blocking the pipe. In reality, the canal is a muscular, vascular, highly flexible structure that changes dimensions throughout the day. The hemorrhoidal cushions themselves are a normal part of its anatomy, present in every healthy person, contributing to the fine continence control that keeps the canal sealed between bowel movements. Problems arise only when those cushions become chronically engorged, stretched, or displaced.
This dynamic nature is why stool shape is not a reliable diagnostic marker for any single condition. The same person can produce stools of different shapes on different days depending on hydration, diet, stress, how long they spent on the toilet, and dozens of other variables. A one-off thin stool is meaningless. Even a few days of thinner stools during a hemorrhoid flare-up are not a cause for alarm. The signal to pay attention to is a sustained, one-directional change that does not fluctuate with dietary adjustments or hemorrhoid management, because that pattern suggests something structural rather than something inflammatory and reversible.