5 Common Causes of Bloody Stool in Babies and What to Do

Bloody stool is usually harmless but can sometimes indicate a medical problem. Learn about some causes of bloody stool in babies and when to call the doctor.

baby sitting on examination table
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As odd as it sounds, you can learn a lot about your little one's development by looking in their diaper. During your baby's first few months, you'll notice plenty of brown, yellow, and green poop—all of which are normal colors for breastfed and formula-fed infants, says Nanci Pittman, M.D., a pediatric gastroenterologist and assistant professor of pediatrics at Mount Sinai School of Medicine in New York City. Blood in baby poop, whether it's small flakes or large streaks, is usually harmless, but it may indicate a medical problem.

Keep in mind: Red poop doesn't always mean blood. It can also be the result of eating red-tinged foods like tomatoes, beets, or even fruit punch. That said, if your little one's stool appears bloody or if it's consistently coming out red, it's important to determine the cause and seek appropriate care.

Most Common Causes of Bloody Stool in Babies

Here are the top causes of bloody baby stool and when to visit the pediatrician.

Constipation

Constipation is fairly common in babies, usually coming from a milk-protein allergy, starting solids, or not getting enough fluids. Telltale symptoms include a prolonged absence of stool, hard poop that looks like pebbles, discomfort, and a firm-feeling belly.

Constipation can also cause tiny tears in the anus (anal fissures), which cause bloody streaks or flakes on the stool's surface. According to the American Academy of Pediatrics, anal fissures are the most common cause of blood in a child's stool. Note that blood from anal fissures will be bright red.

Most anal fissures heal themselves, but if you suspect constipation, try changing your baby's diet. For example, you may try eliminating dairy, adding more fiber, and ensuring they're getting enough fluid. Talk to your doctor for more information on combating constipation.

Infections

Bloody baby stool can also signal certain bacterial and parasitic infections, including gastroenteritis, salmonellosis, shigellosis, staphylococcal infection, Clostridioides difficile (C. diff) infection, or campylobacteriosis. That's because infections often cause intestinal inflammation and tiny ruptures that let blood leak out. Diarrhea commonly comes with infections, so if you notice diarrhea with bloody poop, alert your doctor right away. If there is an infection, they might prescribe antibiotics to help treat it.

Food allergies

Notice bloody poop after changing your baby's diet? You might blame food allergies that inflame the colon, allowing blood to trickle into the stool. The most common food sensitivities in babies are to cow's milk and soy, but your baby could also be allergic to other common food allergens, including eggs, fish, shellfish, tree nuts, peanuts, or wheat.

Food allergies usually present with other symptoms, too, including skin rashes, vomiting, and diarrhea. Your medical provider can help diagnose allergies and develop a treatment plan. (Note that breastfeeding babies can also react to something in their lactating parent's diet).

Parental nipple injuries

If a breastfeeding or chestfeeding parent has cracked and bleeding nipples, the baby could swallow some of the blood while nursing, leading to dark red or black flecks in the stool. This usually isn't cause for concern. However, modifying your baby's latch can prevent or reduce nipple abrasions and soreness. Contact your doctor or a lactation consultant for assistance in adjusting your nursing technique as needed.

Gastrointestinal tract bleeding

In rare cases, dark red or black stool indicates bleeding along the upper gastrointestinal (GI) tract. GI bleeding often comes from a severe illness or injury, so it's vital to alert your doctor immediately if your baby has dark red or black blood in their poop. One common cause of upper GI bleeding in babies is ulcers, so be sure to check with your doctor.

Less Common Causes of Bloody Stool in Babies

Bloody baby stool might also have less common causes. For example, Streptococcus bacteria could infect the skin around the anus, resulting in inflammation and bloody poop. Colitis (inflammation of the large intestine), Crohn's disease, or necrotizing enterocolitis can also cause blood in stool.

When to Call the Doctor

You should always let the pediatrician know about bloody stool, but you should seek care immediately if your baby is younger than 12 weeks old or if you notice any of the following additional symptoms:

  • An excessive amount of blood in the stool
  • Anal injury
  • Black stool
  • Bloody stool with mucus
  • Dark red blood in or on the stool
  • Diarrhea
  • Fatigue
  • Fever
  • Fussiness or inconsolable crying
  • Poop with a tarry consistency
  • Refusal to eat or drink
  • Stomach pain

Make sure to give your doctor a detailed overview of your baby's symptoms. Is the blood dark red or bright red? Does it appear as streaks on the outside of the stool, or is it mixed throughout the poop? Does your baby have fever, diarrhea, or other unusual symptoms? Keeping a detailed log will help your pediatrician reach a diagnosis.

In the office, the doctor may also analyze your baby's stool and examine it for signs of infection or illness. Treatment depends on the exact cause of the bloody stool. Most of the time, though, bloody stool does not result in any long-term health issues.

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