There Is Blood in My Baby's Poop
The short answer
Blood in a baby's stool is always concerning for parents but has many possible causes, ranging from harmless to serious. The most common cause in breastfed babies is swallowed maternal blood from cracked nipples. In formula-fed babies, cow's milk protein allergy is a frequent cause. Other causes include anal fissures (small tears), infections, and rarely, more serious conditions like intussusception. Any blood in your baby's stool should be discussed with your pediatrician, and significant amounts or accompanying symptoms warrant urgent evaluation.
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By Age
What to expect by age
0-3 months
The most common causes of blood in stool in young infants include: swallowed maternal blood (from cracked nipples during breastfeeding or swallowed during delivery — an Apt test can differentiate), cow's milk protein allergy (CMPA, causing bloody, mucousy stools in an otherwise well-appearing baby), and anal fissures (small tears from straining). In a breastfed baby with blood-streaked, mucousy stools who is otherwise well and growing, CMPA is the most likely cause. Your pediatrician may recommend an elimination diet (removing dairy from your diet) or switching to a hypoallergenic formula. Always save the diaper to show your pediatrician.
3-12 months
In addition to the above causes, bacterial infections (Salmonella, Shigella, E. coli) can cause bloody diarrhea, often with fever. Intussusception — where one part of the intestine telescopes into another — typically causes sudden severe abdominal pain (screaming and pulling legs up), "currant jelly" stools (dark red and jelly-like), and lethargy. This is a medical emergency. As solids are introduced, food allergies may cause blood in stool. Anal fissures from hard stools (common during iron supplementation or after introducing certain solids) are also a frequent cause of small amounts of bright red blood on the outside of the stool.
12-36 months
Toddler causes of blood in stool include anal fissures (the most common cause of bright red blood on the stool surface), infections (especially in daycare settings), food allergies, and rarely, polyps (juvenile polyps are usually benign and cause painless rectal bleeding). Bloody diarrhea with fever always warrants medical evaluation. Meckel's diverticulum can cause painless, significant rectal bleeding that may appear as dark red or maroon stool. If your toddler passes large amounts of blood or has "black, tarry" stool (suggesting upper GI bleeding), seek emergency care immediately.
What Should You Do?
When to take action
- A breastfed newborn has a single episode of a small blood streak in the stool and you have cracked nipples — swallowed maternal blood is likely.
- Your baby has a visible small anal fissure and a tiny streak of bright red blood on the outside of a hard stool that resolves with stool softening measures.
- Your pediatrician has evaluated the blood and determined it is from a benign cause that is being monitored.
- You notice blood-streaked or mucousy stools in your baby even if they seem otherwise well — this needs evaluation.
- Blood in stool is occurring repeatedly, not just once.
- Your baby has blood in stool after starting a new food, formula, or supplement.
- Your baby has large amounts of blood in their stool (more than streaks), "currant jelly" appearing stool, or dark black tarry stool — seek emergency care immediately.
- Bloody stool is accompanied by severe abdominal pain (inconsolable screaming, legs drawn up), vomiting (especially green/bile-stained), lethargy, or a distended belly — these could indicate intussusception or another surgical emergency.
- Your baby has bloody diarrhea with high fever, appears very unwell, or has signs of dehydration — seek emergency medical care.
Sources
Related Resources
Trust your instincts. If something feels wrong, reach out to your pediatrician.
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Related Digestive Concerns
I Found Blood in My Newborn's Diaper
Finding blood or red-tinged spots in a newborn's diaper is alarming but often has a benign explanation. Urate crystals (brick-red or orange powder) are very common in the first few days and are harmless. Newborn girls can have a small vaginal discharge or spotting from maternal hormones. However, frank blood in the stool or persistent bleeding always needs medical evaluation.
Mucus in Baby's Poop
Small amounts of mucus in baby poop are quite normal. The intestines naturally produce mucus to help stool pass smoothly. However, consistently large amounts of mucus, especially if accompanied by blood, fussiness, or changes in feeding, can sometimes indicate a food sensitivity, infection, or other digestive issue worth discussing with your pediatrician.
When Does My Baby Need Hypoallergenic Formula?
Hypoallergenic formulas (extensively hydrolyzed or amino acid-based) are recommended for babies with confirmed or strongly suspected cow's milk protein allergy (CMPA). Symptoms of CMPA include blood or mucus in stool, persistent vomiting, severe eczema, hives, or failure to thrive. Your pediatrician should guide the switch to hypoallergenic formula. Partially hydrolyzed formulas (like "gentle" formulas) are not truly hypoallergenic and are not appropriate for babies with confirmed milk allergy.
My Baby's Belly Looks Swollen
A rounded, slightly protruding belly is completely normal in babies and toddlers due to immature abdominal muscles and their proportionally larger organs. However, if the belly becomes suddenly swollen, feels hard and tight, or is accompanied by pain, vomiting, or changes in bowel movements, it needs medical evaluation as it could signal gas buildup, constipation, or rarely, something more serious.
My Baby Has an Anal Fissure (Blood When Pooping)
A small streak of bright red blood on the surface of your baby's stool or on the diaper is most commonly caused by an anal fissure, which is a tiny tear in the skin around the anus from passing hard stool. Anal fissures are very common in babies and toddlers and usually heal on their own with simple measures like keeping stools soft. While this is rarely serious, any blood in your baby's stool should be mentioned to your pediatrician.
Can Antibiotics Damage My Baby's Gut?
Antibiotics can temporarily disrupt your baby's gut microbiome, which may cause loose stools, fussiness, or diaper rash during and shortly after treatment. However, when antibiotics are medically necessary, the benefits of treating the infection far outweigh the temporary gut disruption. Most babies' microbiomes recover within weeks to months, especially with breastfeeding and a gradual return to normal feeding patterns.