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From the YummyYucky team, founded by Nancy Nash

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Blood in a baby's diaper: what causes it, and when should you call?

Red in a diaper stops a parent's heart, so start here: in babies, the most common causes are minor and fixable, and one of the most common "bloods" is not blood at all. A tiny tear from a hard poop is by far the most common cause. That said, blood in a baby's stool is never a finding to shrug off: even when it looks minor, bring it to your pediatrician's attention, and some situations, listed below, mean call right away.

This guide is general information, not medical advice. If your baby is under 12 weeks old, has more than a streak or two of blood, black tarry stools, blood with diarrhea, fever, or seems sick, pale, or unusually sleepy, contact your pediatrician now, and in an emergency contact emergency services.

Cause one, and it is most of them: anal fissures

A large or hard stool can leave a tiny tear at the anus called an anal fissure, and fissures account for about 90% of children with blood in the stool. The signature: a small amount of bright red blood on the surface of the stool or on the wipe, often after visible straining or a firmer-than-usual poop. Fissures heal on their own once stools soften. If hard stools are a theme, our constipation guide covers what helps at each age.

Swallowed blood: the baby is fine, the nipples are not

Babies can swallow blood during delivery and pass it in the first days, and a breastfeeding baby nursing on cracked, bleeding nipples can swallow enough blood for it to show up in spit-up or stool. That blood is the parent's and does not hurt the baby, but tell your pediatrician (so they know the source) and get the latch looked at by a lactation consultant, because nipples are not supposed to bleed.

Milk protein allergy: streaks with a pattern

Cow milk protein allergy can inflame the lower intestine and produce loose, slimy stools streaked with blood, typically starting in the first two months. Unlike a one-off fissure streak, it persists across many diapers and often travels with mucus, fussiness around feeds, spitting up, or slow weight gain. It is very manageable once identified; the pattern is what your pediatrician needs to see, and our CMPA guide explains what happens next.

The great impostor: urate crystals

In the first days of life, a pink, orange, or brick-red stain in the front of the diaper is usually not blood but urate crystals from concentrated newborn urine: powdery, dry-looking, in the urine zone rather than in or on the stool. It is a normal first-week finding that fades as feeding volume climbs. The full story is in our urate crystals guide. Red foods and dyes (beets, tomato skins, colored snacks) pull the same trick in older babies eating solids.

The always-call cases

Contact your pediatrician urgently, or seek emergency care, for:

For a small streak in a well, older baby with none of the above, a call within 24 hours is reasonable; it is most likely a fissure, and your pediatrician can confirm.

Take the photo. Log the date.

Blood in a diaper has a talent for never appearing again until the moment you stop watching, and "reddish, streaky, sometime last week" is thin evidence at an appointment. So: photograph the diaper, note the date and what the stool was like, and keep doing it if it recurs. In YummyYucky, a diaper log takes one tap, and the app's private symptom photos live in the Health tab, walled off from the family feed, so the picture is there for the pediatrician and no one else. A dated series of "streak, streak, nothing, streak" next to the feeding log is exactly the evidence that separates a fissure from a food reaction.

Related reading

See urate crystals in the diaper, cow milk protein allergy, watery poop vs diarrhea, and mucus in baby poop.

This is general information, not medical advice, and blood in the stool is a finding your pediatrician should always hear about, even when this page suggests a benign cause. For the urgent signs listed above, seek care right away, and in an emergency contact emergency services.

Frequently asked questions

What is the most common cause of blood in a baby’s stool?

A tiny tear called an anal fissure, caused by pushing out a large or hard stool. In children with blood in the stool and no diarrhea, fissures account for about 90% of cases. The signature is a small amount of bright red blood on the surface of the stool or on the wipe, often after visible straining or a firmer poop. They heal on their own as stools soften, but contact your pediatrician about any blood you see, even a small streak, ideally within a day.

Can breastfeeding cause blood in baby poop?

Indirectly, yes, in a harmless way: if nipples are cracked and bleeding, the baby can swallow small amounts of blood during feeds, and it reappears in spit-up or stool. Babies can also swallow blood during delivery and pass it in the first days. The blood is the parent’s, not the baby’s, and it is not dangerous to the baby, but it is worth solving the latch or nipple pain with a lactation consultant, and worth telling your pediatrician so they are not chasing the wrong source.

Does blood in the stool mean my baby has a milk allergy?

Sometimes. Cow milk protein allergy can inflame the lower intestine, producing loose, slimy stools streaked with blood, typically starting in the first two months of life. The pattern is persistence: streaks plus mucus across many diapers, often with fussiness around feeds or spitting up, rather than one isolated streak after a hard poop. Bring the pattern (ideally a dated log and a photo) to your pediatrician, who can confirm what is going on and supervise any formula or dietary change.

My newborn has a red-orange stain in the diaper. Is it blood?

Probably not. In the first days of life, a pink, orange, or brick-red powdery stain in the front of the diaper is usually urate crystals from concentrated urine, a normal newborn finding that fades as milk intake rises. Blood, by contrast, shows up as red streaks in or on the stool or around the anus. If the stain persists past the first few days, treat it as a feeding-volume question and mention it at the next check.

When is blood in a baby’s diaper an emergency?

Seek care urgently for: more than a streak or two of blood, blood mixed through the stool, tarry black stools after the first-week meconium days, blood with diarrhea, any blood in a baby under 12 weeks, or a baby who has a fever, is pale, unusually sleepy, in obvious pain, or vomiting. Stool that looks like currant jelly (blood and mucus together) with episodes of severe crying needs emergency evaluation.

Should I take a photo of the diaper for the doctor?

Yes, genuinely. Blood in a diaper is exactly the finding that is gone by appointment time, and “a streak, reddish, Tuesday-ish” is hard to act on. A clear photo plus the date, what the stool was like, and what your baby ate or how they were acting gives your pediatrician the real evidence. It feels odd to photograph a diaper; do it anyway.

Sources

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Last updated September 2026. Next review December 2026. How we write these: built from current published guidance from the AAP, CDC, FDA/EPA, NIAID, WHO, and other pediatric and public-health authorities, with sources cited on the page. See our editorial and medical policy for how we research, source, and update these, and how we double-check the food advice.

This is general information, not medical advice, and is not individualized for your baby. Always talk to your pediatrician about your baby's diet, introducing allergens, and any reaction. In an emergency, contact emergency services.

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