Seeing blood in your child's nappy or on the toilet paper is frightening, even when the amount is tiny. In children, the cause is usually benign and treatable — but blood in the stool is never something to dismiss without a look, because the list of possible causes does include a few serious ones.
The good news is that what the blood looks like — bright red versus dark, on the surface versus mixed through, a smear versus a clot — tells you a lot about where it's coming from and how urgently it needs attention.
Healthbooq (healthbooq.com) covers digestive health through the early years, including which symptoms need a same-day GP review.
Reading the Blood
Bright red blood on the surface of the stool or on the toilet paper, with nothing mixed through the stool itself, almost always means bleeding from the anus or rectum. This is the most common pattern in children and usually points to an anal fissure (a small tear), a polyp, or inflammation of the rectal lining.
Blood mixed through the stool suggests bleeding higher up — somewhere in the colon. The colour tends to be darker red or maroon. Infectious gastroenteritis from Campylobacter, Salmonella, or certain strains of E. coli can cause bloody diarrhoea where blood is mixed through loose stools.
Dark, sticky, tarry stool (melaena) means the blood has come from the stomach or small intestine and has been partially digested on its way through. It has a distinctive, strong smell and looks more like black tar than ordinary stool. This always needs urgent assessment.
Red stool that isn't actually blood is a common source of false alarms. Beetroot, red food colouring in sweets and drinks, tomato-heavy meals, and the dye in some medications can all turn stool red without any bleeding at all. A dietary history usually clarifies it; if there's any doubt, your GP can do a quick test for blood.
Common Causes by Age
Newborns. A common and entirely benign cause is swallowed maternal blood — either from delivery or from a cracked nipple during breastfeeding. The Apt test, which a midwife or paediatrician can do, distinguishes maternal blood (adult haemoglobin, breaks down in alkali) from the baby's own blood. If it's maternal, no treatment is needed. Necrotising enterocolitis (NEC) is the serious cause to know about in this age group: it primarily affects premature or sick newborns and is managed in the neonatal unit.
Infants. Cow's milk protein allergy (CMPA) is a common cause of small streaks of bright red blood, often with mucus and looser stools. Switching to an extensively hydrolysed formula, or — if breastfeeding — eliminating dairy from the mother's diet, usually resolves it within two to four weeks. Anal fissures are also very common at this age, often from passing a hard stool, and produce bright red blood on the outside of the stool or on the nappy, sometimes with visible discomfort during a poo.
Toddlers. Anal fissures are the most common cause. Intussusception, where one part of the bowel telescopes into another, is the surgical emergency to know about: classic features are episodic severe pain, drawing the legs up, and "redcurrant jelly" stool (a mix of blood and mucus) — though redcurrant jelly is a late sign, and its absence doesn't rule out the diagnosis. Juvenile polyps are benign growths on the colon wall, fairly common in this age group, that cause painless bright red rectal bleeding. They're not pre-cancerous in children (unlike colonic polyps in adults) but they should be identified and removed by colonoscopy.
Older children. Anal fissures from constipation are still the most common cause, especially in children who have been holding poo. Infectious gastroenteritis, particularly Campylobacter, can cause bloody diarrhoea — typically with fever, abdominal pain, and frequent loose stools. Most cases settle in five to seven days without antibiotics, though Campylobacter is sometimes treated with azithromycin in severe or prolonged illness. Inflammatory bowel disease — Crohn's and ulcerative colitis — is much less common but worth thinking about in a child with persistent or recurrent symptoms, especially when there's also weight loss, growth failure, fatigue, or chronic abdominal pain.
When to Seek Urgent Help
Go to A&E or call 999 if: there is a large quantity of blood; the child is pale, floppy, or lethargic; there is significant or episodic abdominal pain; the stool is black and tarry; or the bleeding is in a newborn.
See a GP the same day or next day if: there is blood mixed through the stool (rather than only on the surface); there are repeated episodes; there's any blood combined with fever, diarrhoea, or significant abdominal pain; or you simply can't account for what you're seeing.
A non-urgent GP appointment is fine for a small streak of bright red blood on a hard stool in a child who is otherwise well, eating normally, and has no other symptoms — that pattern is almost always a fissure, but it's still worth getting confirmed.
Key Takeaways
Blood in a child's stool is alarming for parents and warrants assessment, though most causes in children are benign. The most common causes by age group are: in newborns, swallowed maternal blood (Apt test distinguishes this from infant bleeding) or anal fissure; in infants, cow's milk protein allergy or anal fissure; in toddlers, anal fissure, polyps, or intussusception; in older children, constipation with fissures, infectious gastroenteritis, or rarely inflammatory bowel disease. Bright red blood on the surface of the stool or on toilet paper suggests an anal source (fissure or polyp). Dark or black tarry stool suggests bleeding higher in the digestive tract. Any significant quantity of blood, blood mixed through the stool, or blood with systemic symptoms (pallor, lethargy, significant abdominal pain) requires same-day assessment.
