Blood in Stool: Common Causes and When to Get Checked
Seeing blood when you go to the loo is unsettling. Most of the time the cause is something common and fixable, like piles or a small tear in the skin around your bottom. But blood can also be a sign of something that needs a proper look, including bowel cancer, so it’s worth knowing what’s likely, what’s not, and when to pick up the phone.
Let’s be real: nobody loves talking about this. This guide walks you through the usual suspects, what the colour of the blood can tell you, and the point at which you should stop googling and speak to a professional.
TL;DR
- Bright red blood is most often down to piles (haemorrhoids) or an anal fissure, according to the NHS.
- Black or very dark poo can point to bleeding higher up in the gut, though iron tablets and some foods can darken it too.
- A small, one-off bit of blood is not usually serious, but see a GP if blood or a change in your pooing habits lasts 3 weeks.
- Lots of blood, non-stop bleeding or big clots means A&E or 999, not waiting it out.
- A home test can’t explain visible blood. If you can see it, speak to a GP.
Table of Contents
- What blood in your stool can look like
- The most common causes of blood in stool
- Quick guide: what the colour might suggest
- When to see a GP, call 111 or go to A&E
- How doctors find the cause
- Where home testing fits (and where it doesn’t)
- Our perspective
- Things you can do while you wait for your appointment
- FAQ
- Sources
What blood in your stool can look like
Bleeding from the bottom doesn’t always look the same. The NHS describes several signs of rectal bleeding:
- blood on the toilet paper after wiping
- red streaks on the outside of your poo
- pink or red water in the toilet bowl
- blood mixed into your poo, or bloody diarrhoea
- very dark poo
The look of it gives clues, though not answers. Fresh, bright red blood usually means the bleeding is close to the exit: the rectum or anus. Darker red, maroon or black poo suggests the blood has travelled further and been partly digested, so the source may be higher up, in the stomach or small bowel.
Doctors use the term “rectal bleeding” for blood coming from the bottom, and you’ll also see “haematochezia” for fresh red blood in the stool. Same thing, fancier word.
The most common causes of blood in stool
The NHS lists the usual causes of bright red bleeding as piles, anal fissures and some STIs such as genital warts. Scottish NHS guidance on acute lower gut bleeding adds that most fresh red or purple blood or clots come from haemorrhoids or diverticular disease, and over 90% of cases settle on their own. That’s reassuring, but it’s a reason to get checked sensibly, not a reason to ignore it.
Piles (haemorrhoids)
Piles are swollen blood vessels in or around the back passage. They often cause bright red blood on the paper or in the bowl, sometimes with itching or a lump. Straining, constipation and sitting for long stretches make them more likely. They tend to bleed without much pain.
Anal fissure
A fissure is a small tear in the lining of the anus, often after passing a hard stool. The classic sign is a sharp, stinging pain when you poo, followed by a streak of bright red blood. It’s very common and often heals with simple measures, but a GP can help if it keeps coming back.
Diverticular disease and diverticulitis
Diverticula are small pouches that can form in the bowel wall. They can bleed, sometimes with little warning. When they become inflamed (diverticulitis), NHS commissioning guidance describes constant tummy pain, usually low on the left, a change in bowel habit and sometimes rectal bleeding. That combination deserves a prompt GP appointment.
Gastroenteritis and infections
A stomach bug can cause bloody diarrhoea, and the NHS lists gastroenteritis among the possible causes. If you’ve got bloody diarrhoea, don’t just wait for it to pass: the NHS advises asking for an urgent GP appointment or getting help from NHS 111.
You may have seen parasites and spicy food mentioned online. The NHS rectal bleeding page doesn’t name either as a cause, so we won’t claim they are. Spicy food can irritate an already sore bottom, but unexplained blood needs checking rather than blaming on last night’s curry.
Inflammatory bowel disease (IBD)
Ulcerative colitis and Crohn’s disease cause long-term inflammation in the gut. NHS guidance says IBD should be considered in people with new profuse diarrhoea, with or without rectal bleeding, that doesn’t settle on its own. Other clues include tummy cramps, tiredness and weight loss.
Medicines
Blood thinners and some pain relievers can make bleeding more likely. The NHS names warfarin, apixaban and aspirin as medicines that can cause bright red bleeding or dark or black poo. Never stop a prescribed medicine on your own. Call your GP or pharmacist and tell them what you’ve seen.
Peptic ulcers and upper gut bleeding
Sores in the stomach or the first part of the small bowel can bleed. Because the blood is digested on the way through, it typically shows up as black, tarry, strong-smelling poo rather than bright red. That’s the type of dark poo the NHS says to get seen about quickly.
Bowel cancer
This is the one most people are quietly worried about. The NHS is clear that bleeding from the bottom is sometimes a sign of bowel cancer, and that it’s easier to treat when found early. It’s far from the most likely cause, but it’s the reason a lingering change shouldn’t be brushed off.
Quick guide: what the colour might suggest
| What you see | Often linked to | What to do |
|---|---|---|
| A few spots on the paper, bright red | Piles, anal fissure | If it’s a one-off, keep an eye on it. See a GP if it lasts 3 weeks |
| Bright red streaks on the poo | Piles, fissure, sometimes other causes | Same as above, and sooner if you have pain or other symptoms |
| Blood mixed through the poo | Can be a sign of something higher in the bowel | Book a GP appointment |
| Black or very dark red poo | Bleeding higher up, certain medicines, or harmless causes like iron tablets | Ask for an urgent GP appointment or call NHS 111 |
| Bloody diarrhoea | Infection, IBD and other causes | Urgent GP appointment or NHS 111 |
| Lots of blood, red toilet water, big clots, or non-stop bleeding | Needs emergency care | A&E or 999 |
The actions in the table follow the NHS advice on rectal bleeding. The NHS also notes that iron tablets or dark foods can make poo look dark, so a single dark stool after beetroot or iron supplements isn’t automatically a worry. Black, tarry poo that keeps happening is a different story.
When to see a GP, call 111 or go to A&E
Here’s how the NHS splits it.
Go to A&E or call 999 if
- the bleeding won’t stop
- there’s a lot of blood, such as the toilet water turning red
- you’re passing large blood clots
Ask for an urgent GP appointment or get help from NHS 111 if
- your poo is black or dark red
- you have bloody diarrhoea
Book a GP appointment if
You should contact a GP if blood in your poo or a change in your pooing habits lasts 3 weeks, or if you have:
- a lot of pain around your bottom
- tummy pain or a lump
- unusual tiredness
- unexplained weight loss
Children with blood in their poo should also see a GP. A small amount of one-off bleeding isn’t usually a serious problem, but a GP can still check if it’s worrying you. You are never wasting anyone’s time.
Age matters
Risk of bowel cancer rises with age, and GPs take that into account. In NHS guidance, people aged 40 to 60 with persistent rectal bleeding (over 6 weeks) and looser or more frequent stools, and people over 60 with persistent bleeding without anal symptoms and/or looser or more frequent stools, meet the criteria for a two-week-wait referral. Referral rules differ by area and change over time, so your GP will decide what’s right for you.
How doctors find the cause
It’s usually less dramatic than people fear. According to the NHS, a GP may examine your back passage with a gloved finger, ask for a poo sample to be tested, or refer you to a specialist for further tests.
If you have diarrhoea and tummy symptoms, your GP might also think about a faecal calprotectin test. Guidance for primary care describes it as a useful way to tell IBD from IBS, which can help avoid unnecessary referrals. In hospital, someone who is bleeding heavily and unstable may have a CT angiogram to pinpoint where the blood is coming from, as Scottish NHS guidance describes.
For your appointment, it helps to note:
- when you first noticed blood and how often it happens
- the colour and amount (on paper, on the poo, in the bowl)
- any pain, diarrhoea, constipation or change in habits
- weight loss, tiredness or a lump
- every medicine and supplement you take, especially blood thinners, aspirin and iron
Where home testing fits (and where it doesn’t)
Here’s the honest bit. If you can already see blood in your poo, a home test isn’t the answer. It can’t tell you why you’re bleeding, and a “negative” shouldn’t talk you out of seeing a doctor. Visible blood, black stools, pain or weight loss all need a GP.
What home testing is good for is the quiet stuff: checking in before symptoms show up, especially if you’re in a higher-risk group. The NHS bowel screening programme uses a home test called FIT to look for hidden blood in a poo sample, and is currently offered every 2 years to people aged 50 to 74. If you’re outside that window, or you simply want to keep an eye on things, a home screening kit is a convenient extra step.
And one cause of bleeding is easy to overlook: STIs. The NHS lists them among the possible causes of bright red bleeding from the bottom. If you’ve had unprotected sex and notice blood, soreness or discharge, testing for infections is a sensible move alongside seeing a clinician.
Rapidtest kits worth knowing about
At Rapidtest we make at-home rapid test kits that give results in about 15 minutes, with full instructions and discreet packaging. Our men’s health screening range includes FOB (faecal occult blood) and PSA tests, designed for people who want to screen for bowel and prostate concerns in private. If you’re wondering about infections, our at-home STI test kits start from £21.95, and our kits are CE-certified, with free UK shipping and a 60-day refund guarantee if a kit doesn’t work.
You can browse the full range on the Rapidtest homepage. A kit is a screening tool, not a diagnosis, so a positive result means a GP visit, and visible blood means a GP visit whatever any test says.
Our perspective
We hear a version of the same story a lot: someone notices a bit of blood, tells themselves it’s piles, and then months go by. Embarrassment does more damage here than the symptom itself.
Our view is simple. Most causes are harmless and treatable, and that’s exactly why checking early is easy to put off and worth doing anyway. We built Rapidtest around people who are busy, a bit anxious, or just don’t fancy sitting in a waiting room to discuss their bottom. A private 15-minute screen at home can lower the barrier to taking the first step, but it never replaces a doctor when you have symptoms.
So here’s our rule of thumb. If blood is visible, call your GP. If you feel fine and want to stay on top of your bowel and prostate health, screening at home is a smart, low-fuss habit. Either way, you’re doing the right thing by paying attention.
— Jack
Things you can do while you wait for your appointment
None of this replaces advice from a clinician, and none of it should delay a GP visit if you have the warning signs above. But if piles or a fissure are the likely culprits, these everyday habits make life easier:
- Don’t strain. Give yourself time, and don’t sit on the loo scrolling for ages.
- Go when you need to. Holding it in can make stools harder.
- Keep a note. A simple diary of what you see and when makes the GP conversation quicker.
- Be gentle when wiping. Pat rather than scrub.
- Check your medicines. If you take aspirin or a blood thinner, mention it to your GP or pharmacist.
If the bleeding is getting heavier, or new symptoms appear, don’t wait for the three-week mark. The three weeks is a limit for mild, otherwise well situations, not a target to hit.
FAQ
Is blood in stool always serious?
No. A small amount of one-off bleeding is not usually a serious problem, according to the NHS, and common causes like piles and fissures are harmless. But it can occasionally signal something more serious, so a GP can check if it’s worrying you or it doesn’t go away within 3 weeks.
Can piles cause blood in stool?
Yes, piles are one of the most common causes of bright red blood on the paper, the poo or in the toilet. They often bleed without much pain. Because other conditions can look similar, see a GP if the bleeding keeps happening or comes with other symptoms.
Why is my poo black?
Black or very dark poo can mean bleeding in the stomach or gut, and some medicines such as aspirin or blood thinners can contribute. Iron tablets and dark foods can also darken stools. If it’s black or dark red and you aren’t sure why, the NHS advises asking for an urgent GP appointment or contacting NHS 111.
Can blood in stool be a sign of bowel cancer?
Sometimes, yes. Bowel cancer is easier to treat when found early, so see a GP if blood in your poo or a change in your pooing habits lasts 3 weeks, or if you also have tummy pain, a lump, unusual tiredness or unexplained weight loss.
Can a home test tell me why I have blood in my stool?
No. A home screening kit can’t identify the cause of visible bleeding, and it shouldn’t replace a GP appointment. If you can see blood, speak to a doctor.