Faecal Impaction and Overflow Soiling
Why leaking loose stool is usually a sign of a blockage rather than diarrhoea, how impaction is cleared, and why it comes back when the second half is skipped.
Part of the Complete Constipation Guide.
Key fact: Watery stool leaking around a blockage is the commonest way impaction presents — and it is routinely mistaken for diarrhoea. Taking an anti-diarrhoeal such as loperamide in that situation makes it considerably worse.
What impaction is
Faecal impaction is a mass of hard stool that has become too large and too dry to pass. It usually forms in the rectum, sometimes higher in the colon, and it is the end point of constipation that has gone on too long without being addressed.
Once it has formed, ordinary laxative doses are not enough. The mass itself has to be cleared before normal treatment can work, which is why the regimens used are different from everyday constipation management.
Overflow soiling: the trap
This is the part that matters most, because it produces exactly the wrong instinct.
Liquid stool from higher up the bowel seeps around the impacted mass and leaks out. To the person experiencing it, that is diarrhoea — loose, sometimes uncontrollable, often at night or without warning. The natural response is to take something to stop it.
Anti-diarrhoeals such as loperamide slow the bowel further and make impaction worse. If loose stool or soiling comes with a feeling of being blocked, a swollen abdomen, or a long stretch without a proper bowel movement, treat it as possible impaction and get advice rather than reaching for an anti-diarrhoeal.
Overflow is commonest in older or less mobile people, and in those on opioids — see opioid-induced constipation. It is also a recognised cause of new faecal incontinence, which is frequently attributed to age when the real cause is treatable.
Who it happens to
- Older adults, particularly with reduced mobility or in residential care
- Anyone on regular opioids, including co-codamol
- People with neurological conditions — Parkinson's disease, multiple sclerosis, spinal cord injury or stroke
- Anyone recently immobile — after surgery, a fracture, or a period in hospital
- People with longstanding untreated constipation, where the rectum has stretched and lost sensation
- People who have avoided opening their bowels because of pain from a fissure or haemorrhoids
How to recognise it
| Symptom | Why it happens |
|---|---|
| No proper bowel movement for days, despite the urge | The mass will not pass |
| Loose stool or soiling, sometimes unnoticed until it happens | Overflow around the mass |
| A swollen, uncomfortable abdomen | Loading above the blockage |
| Feeling full quickly, poor appetite, nausea | Pressure and slowed transit |
| Straining with only small hard fragments passed | Pieces breaking off the mass |
| New confusion or agitation in an older person | A recognised and easily missed presentation |
| Difficulty passing urine | A loaded rectum pressing on the bladder |
Diagnosis is usually made by examination — feeling the abdomen and examining the rectum — rather than by scan.
How it is treated
In sequence, and under direction rather than improvised:
| Step | What it involves |
|---|---|
| Confirm it, and exclude obstruction | Impaction and bowel obstruction can look similar and are treated very differently. This is why it starts with an examination rather than a purchase. |
| High-dose oral macrogol for hard stool | The licensed disimpaction regimen, set out below. |
| Add a stimulant if needed | Where stool has softened but is still not moving. |
| Suppository or mini enema if the oral route is not enough | Acting directly on what is sitting in the rectum. |
| Retention enema, or manual evacuation, if still inadequate | Done by a clinician. |
Bulk-forming laxatives are not used for impaction. Adding bulk above a blockage is the opposite of what is needed.
The high-dose macrogol regimen
The licensed adult regimen for faecal impaction is markedly different from everyday dosing:
| Ordinary constipation | Faecal impaction | |
|---|---|---|
| Sachets per day | 1 to 3, in divided doses | 8 |
| Over what period | Through the day | All within a 6-hour period |
| Duration | Usually up to 2 weeks | No more than 3 days |
| Made up in | 125ml of water per sachet | 8 sachets may be dissolved in 1 litre of water |
Anyone with impaired cardiovascular function should take no more than two sachets in any one hour, because of the fluid and salt load. This regimen is directed by a clinician, not started independently — it needs impaction confirmed and obstruction excluded first.
Expect it to be unpleasant and to require access to a toilet. A day at home is a sensible plan. The macrogol guide covers ordinary dosing and how to make it more palatable.
When oral treatment is not enough
- Glycerol suppositories soften and lubricate stool in the rectum, working within about 15 to 30 minutes
- Bisacodyl suppositories stimulate the rectum directly
- Sodium citrate mini enemas are small-volume and often better tolerated than they sound
- Phosphate or arachis oil retention enemas are used for more resistant loading, by a clinician
- Manual evacuation is occasionally necessary and is a clinical procedure
There is no virtue in enduring an oral regimen that is not working when the obstruction is two inches from the exit.
Afterwards: the part that gets skipped
Clearing the impaction is half the job. Without maintenance, it re-forms — and a rectum that has been stretched by a large mass has reduced sensation for a period, which makes recurrence more likely rather than less.
- Continue a maintenance laxative, usually macrogol at an ordinary dose, for weeks to months
- Address the cause — opioids, immobility, low fibre and fluid, a medicine that can be changed
- Re-establish a routine, using the period after breakfast, with a footstool and without prolonged straining
- Do not stop abruptly when things improve; reduce gradually
- Treat anything that makes opening the bowels painful, such as a fissure or haemorrhoids, because avoidance is what started the cycle for many people
When it is an emergency
Seek same-day assessment, or call 999 if severe, for: severe or worsening abdominal pain; vomiting, particularly if you cannot keep fluids down; inability to pass wind as well as stool; a distended, tense, tender abdomen; fever; or new confusion in an older person. These raise the possibility of bowel obstruction or perforation, which need urgent assessment rather than more laxative.
Frequently Asked Questions
Can constipation cause diarrhoea?
It can appear to. Liquid stool from higher in the bowel seeps around a mass of impacted stool and leaks out, which is called overflow soiling and is routinely mistaken for diarrhoea. Taking an anti-diarrhoeal such as loperamide in that situation slows the bowel further and makes the impaction worse.
What are the signs of faecal impaction?
No proper bowel movement for days despite the urge, loose stool or soiling leaking out, a swollen and uncomfortable abdomen, feeling full quickly with nausea, straining that produces only small hard fragments, and sometimes difficulty passing urine or new confusion in an older person.
How is faecal impaction treated?
After confirming it and excluding obstruction, the usual first step is a high-dose oral macrogol regimen, with a stimulant laxative added if stool softens but does not move. If the oral route is not enough, a suppository or mini enema is used, and occasionally a retention enema or manual evacuation.
How many Movicol sachets are used for impaction?
The licensed adult regimen is 8 sachets daily, all taken within a 6-hour period, for no more than 3 days, and the 8 sachets may be dissolved together in one litre of water. Anyone with impaired cardiovascular function should take no more than two sachets in any one hour. It is a clinician-directed regimen.
Why does impaction keep coming back?
Because clearing it is only half the treatment. A rectum stretched by a large mass has reduced sensation for a period, so without a maintenance laxative and without addressing the underlying cause, it re-forms. Maintenance usually continues for weeks to months and is reduced gradually.
References
- NHS. Constipation. nhs.uk
- National Institute for Health and Care Excellence. Clinical Knowledge Summary: Constipation. cks.nice.org.uk
- Electronic Medicines Compendium. Movicol 13.7g powder for oral solution: Summary of Product Characteristics. medicines.org.uk
- National Institute for Health and Care Excellence. Suspected cancer: recognition and referral (NG12). nice.org.uk
- National Institute for Health and Care Excellence. Quantitative faecal immunochemical testing to guide referral for colorectal cancer in primary care (DG56). nice.org.uk
Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. A persistent change in bowel habit, rectal bleeding or unexplained weight loss should always be assessed rather than treated as constipation. Always consult a qualified healthcare professional for diagnosis and treatment. In a medical emergency, call 999.