Causes
Blood in the stool is a sign, not a diagnosis, and the likely cause depends on your child’s age, what the blood looks like, and what else is happening. A well, growing child with a few bright red streaks has a very different set of likely causes than a child with bloody diarrhea and a fever.
What the blood looks like, and what it can mean
The color and the pattern help your clinician diagnose the cause:
- Bright red streaks on the outside. The blood coats the surface of the stool or shows on the wipe. This pattern points to the anus or the last part of the bowel.
- Red or dark red blood mixed into the stool. The blood is mixed in rather than coating the outside. This pattern points to bleeding higher up in the large bowel.
- Blood together with mucus. Mucus is the clear or whitish slime that can coat stool. In a baby, blood and mucus together often point to a food allergy or an infection.
- Black, tarry stools. Blood becomes black after it’s digested. This usually means the bleeding started in the stomach or the upper bowel, and it needs emergency care.
A small amount of blood spreads a long way in water. A stool with a few streaks can color a whole toilet bowl pink. That does not mean your child has lost a lot of blood.
Common causes in babies under 1 year
- A small tear at the anus. A hard or large stool stretches the skin until it splits. Clinicians call this an anal fissure. It leaves bright red streaks on the outside of the stool, and your baby may cry while passing it. This is the most common cause of blood in the stool in babies and toddlers.
- Cow’s milk protein allergy. The baby’s immune system reacts to milk protein, which reaches them through formula or through the breastfeeding parent’s diet. It causes blood and mucus in loose stools in a baby who otherwise looks well and is gaining weight. Cow’s milk allergy affects about 2-3% of infants.
- Blood the baby swallowed. A newborn can swallow the parent’s blood during birth or from a cracked nipple during feeding. That blood passes through the gut and then shows up in the stool. A lab test called the Apt test can confirm the diagnosis and show whose blood it is.
- A gut infection. Germs that infect the bowel lining cause loose stools with blood. A viral gut infection caused about one in 10 cases in a study of 300 newborns admitted for bloody stools.
Common causes in toddlers and older children
- Constipation and a tear at the anus. Hard stools are the usual reason older children bleed. The American Academy of Pediatrics (AAP) notes that the blood is bright red, small in amount, and often shows only on the toilet paper. The AAP also reports that constipation accounts for about one in 20 visits children make to a clinician. Our Constipation in Children page covers treating the cause.
- A gut infection. Bacteria such as Salmonella, Shigella, Campylobacter, and E. coli (germs that infect and inflame the bowel lining) cause diarrhea with blood, usually with cramps. The Centers for Disease Control and Prevention (CDC) notes that fever is common with some of these germs, and mild or absent with others.
- A small growth on the bowel lining. Clinicians call this a juvenile polyp. It causes bright red bleeding that does not hurt, which is what separates it from a tear at the anus.
- Long-term swelling of the bowel lining. Clinicians call this inflammatory bowel disease. It causes blood alongside diarrhea, belly pain, and slow weight gain over weeks or months, rather than one short episode.
Less common causes that need quick attention
- One part of the bowel sliding into the next. Clinicians call this intussusception (when one part of the bowel slides inside the next part). It causes belly pain that comes and goes in waves, vomiting that may become green, and stools mixed with blood and mucus. Children often pull their knees to their chest during a wave of belly pain, and some become very drowsy in between. It is most common between 6-36 months of age. You may read that intussusception produces a “currant jelly” stool, but stools that truly look like that appear in only a minority of cases. Any bloody stool in a child with waves of belly pain warrants quick action.
- A pouch left in the bowel from before birth. Clinicians call this a Meckel diverticulum (a small pouch on the small bowel that never closed off). It causes bleeding that does not hurt, and the bleeding can be heavy.
- Swelling of small blood vessels. Clinicians call this IgA vasculitis, and its older name is Henoch-Schönlein purpura. A child gets a spotty purple rash on the legs, feet, or buttocks, along with belly pain, sore joints, and sometimes blood in the stool.
- A serious kidney problem after bloody diarrhea. Clinicians call this hemolytic uremic syndrome (a kidney problem that can follow some gut infections). The CDC reports that eight in 10 children who develop it have had an infection with a Shiga toxin-producing type of E. coli, and it’s most common in children younger than 5 years.
Things that look like blood but are not
Foods and medicines color stool. MedlinePlus, from the National Library of Medicine, notes that a clinician can test a stool sample with a chemical to check whether blood is actually there.
- Red foods and drinks. Beets and foods containing red coloring can make stool look reddish.
- Foods and medicines that darken stool. Black licorice, blueberries, iron pills, and medicines containing bismuth can make stool black.
For red coloring, the difference is the pattern. Food coloring tints the whole stool evenly, and blood from a tear at the anus streaks the surface.
For black stool, there is no difference a parent can see at home. Iron pills and licorice blacken stool, and so does digested blood, so black stool always needs a clinician to tell the two apart.
Spotting the rash and the loss of color on brown and dark skin
A purple rash and paleness may look different on dark skin. Here is what to check.
- Press the spots. A rash caused by bleeding under the skin does not fade when you press it briefly. Spots that stay visible under pressure need a clinician.
- Feel for texture. The rash of IgA vasculitis can be felt as raised bumps.
- Check the places where color shows. A loss of color is easier to see inside the lower eyelids, in the gums and the lining of the mouth, on the palms, and in the nail beds than on the arms or legs. The CDC names the cheeks and the inside of the lower eyelids as places to check.
- Use daylight and compare. Look at your child in natural light, and compare the area with nearby skin or with a family member.
Tell your clinician what you saw and where you looked. Your clinician will act on those findings the same way they act on redness in a lighter-skinned child.
