What Causes Hemorrhoids
Hemorrhoids develop from abnormal swelling and distal displacement of the normal anal cushions—vascular structures in the anal canal—though the exact pathogenesis remains unknown, and rigorous proof for most commonly cited risk factors (including constipation, straining, and prolonged toilet sitting) is actually lacking. 1
Understanding the Pathophysiology
The American Gastroenterological Association explains that hemorrhoids arise through a specific structural failure rather than simple venous congestion 1:
- Normal anal cushions are fibrovascular structures containing connective tissue surrounding arteriovenous communications between terminal branches of the superior rectal arteries and rectal veins 1
- These cushions are suspended by smooth muscle arising from the conjoined longitudinal muscle layer 1
- Symptomatic hemorrhoids occur when these cushions become abnormally enlarged, causing stretching of the suspensory muscles and prolapse of upper anal and lower rectal tissue through the anal canal 1
- The vascular channels undergo abnormal dilatation and distortion, with destructive changes in the supporting connective tissue 2
Physiologic Abnormalities
The most consistent finding in hemorrhoid patients is elevated anal resting pressure 1:
- Patients with hemorrhoids demonstrate increased maximum resting anal pressure compared to controls 1
- Whether this elevated pressure causes hemorrhoids or results from them remains unclear 1
- Resting tone normalizes after hemorrhoidectomy, suggesting it may be a consequence rather than a cause 1
- Dysregulation of vascular tone and vascular hyperplasia may play important roles in hemorrhoidal development 2
Commonly Believed Risk Factors (Lacking Rigorous Proof)
The American Gastroenterological Association emphasizes a critical caveat: most widely believed risk factors lack rigorous scientific proof 1:
- Inadequate fiber intake - widely believed by clinicians but not rigorously proven 1
- Prolonged sitting on the toilet - commonly cited but lacking rigorous proof 1
- Chronic straining at stool - believed to contribute but not rigorously proven 1
- Constipation and diarrhea - proposed as contributing factors but none rigorously proven 1
- Family history - suggested but not rigorously proven 1
Despite the lack of rigorous proof, constipation and increased intra-abdominal pressure with prolonged straining are still commonly implicated in clinical practice 3.
Pregnancy as a Special Circumstance
Pregnancy represents the one clearly documented association 4, 1:
- Hemorrhoids occur in approximately 80% of pregnant persons, most commonly during the third trimester 4, 1
- The mechanism involves compression of the rectum by the gravid uterus 4
- Only 0.2% of pregnant women require urgent hemorrhoidectomy for incarcerated prolapsed hemorrhoids, indicating severe complications remain rare despite high prevalence 1
Important Clinical Pitfall
Portal hypertension does NOT cause hemorrhoids 4: