How do I know if my baby has diarrhea?

Diarrhea in babies means a sudden change from their normal: stools become much more watery or liquid, and frequency doubles or triples. One loose diaper isn't diarrhea - it's the pattern that matters. Compare to your baby's usual baseline. Breastfed babies normally have loose, watery stools, so diarrhea means even looser and more frequent than that.

What does baby diarrhea look like?

Baby diarrhea typically looks like juice or water rather than paste. It may be bright green, contain mucus, smell sharply different from normal (often very sour), and be explosive. The key sign is that it's a clear change from your baby's usual pattern and it happens multiple times in a row.

How long should baby diarrhea last?

Most viral diarrhea in babies passes within 5-7 days. Call your pediatrician if it lasts more than 7 days, if baby shows signs of dehydration (fewer than 6 wet diapers in 24 hours, no tears, sunken fontanelle), or if your baby is under 3 months old with any diarrhea.

What are signs of dehydration in babies?

Watch for: fewer than 6 wet diapers in 24 hours (fewer than 4 for babies under 6 months), no tears when crying, dry mouth and lips, a sunken soft spot on top of the head, unusually sleepy or hard to wake, and dark yellow urine. Mild dehydration: call your pediatrician. Sunken fontanelle or hard to wake: go to the ER.

Can teething cause diarrhea in babies?

Mild stool loosening during teething is reported by many parents and some pediatricians - likely from swallowing more saliva. But teething shouldn't cause true diarrhea (multiple very watery stools per day). If your baby has significant diarrhea during teething, look for another cause like a viral illness.

Baby Diarrhea vs. Normal Poop: How to Actually Tell the Difference

Newborn poop already looks alarming. Yellow, watery, seedy - nothing like what you expected. So when it changes, how are you supposed to know if something's wrong?

The honest answer: one loose diaper isn't diarrhea. Diarrhea is when frequency suddenly doubles or triples and the consistency becomes noticeably more watery - and it stays that way. A single odd diaper usually means nothing.

What normal poop looks like first

You need a baseline before you can spot a change.

Breastfed babies: Yellow or mustardy, often seedy or pasty, loose to the point of looking watery. Frequency ranges from after every single feeding (8-12 times/day in the first weeks) to once every several days after 6 weeks. Both are normal.

Formula-fed babies: Tan to yellow-brown, noticeably firmer than breastfed poop, usually 1-4 times per day. Smells stronger.

Once solids start: Changes dramatically and constantly depending on what they ate. Brown, green, orange - all possible. You'll recognize chunks of last night's dinner in there. Totally normal.

What diarrhea actually looks like

Compared to your baby's normal:

More watery or liquid in consistency - may look like juice rather than paste
Significantly more frequent (if a formula-fed baby who usually goes twice a day suddenly goes 6 times, that's a change worth noting)
Smell changes - often sharper, more sour
May be explosive, or contain mucus
Often green-tinged when it's caused by illness

The pattern matters as much as any single diaper. One watery poop isn't diarrhea. Three to four watery poops in a row that represent a clear change from normal - that's diarrhea.

Normal vs diarrhea: at a glance

Feature	Normal baby poop	Diarrhea
Breastfed texture	Loose, seedy, pasty	Very watery, like juice
Formula texture	Soft to firm	Very loose, possibly mucusy
Frequency	Baby's usual range	Doubles or triples suddenly
Color	Yellow to brown to green	Often bright green or brown
Smell	Mild (breastfed) or moderate (formula)	Sharply different, sour
Baby's behavior	Normal between changes	Irritable, less interested in feeding

What causes diarrhea in babies

The most common cause by a wide margin: a viral stomach bug. Same as what adults get. It usually passes in 5-7 days.

Other causes worth knowing about:

Antibiotics - they wipe out good gut bacteria along with the bad, and loose stools are a very common side effect. Talk to your doctor about giving probiotics alongside the course.
New food introduction - sometimes a single food causes temporary loosening, especially high-fiber foods like prunes or pears
Milk protein allergy - diarrhea (often with mucus or blood) that persists beyond a week, sometimes with fussiness and skin rash. See our full guide on milk protein allergy and baby poop.
Teething - controversial, but many parents and some pediatricians report mild stool loosening during teething. It shouldn't be severe diarrhea

The part that actually matters: dehydration signs

Diarrhea itself isn't usually the danger. Dehydration from diarrhea is. Here are the signs to watch for:

Fewer than 6 wet diapers in 24 hours (for babies under 6 months: fewer than 4)
No tears when crying
Dry mouth and lips
The soft spot on top of the head (fontanelle) looks sunken
Baby seems unusually sleepy or hard to wake
Urine looks dark yellow or amber instead of pale

Mild dehydration: call your pediatrician. Moderate to severe (sunken fontanelle, no tears, lethargic): go to the ER.

When to call the doctor

Diarrhea lasting more than 7 days
Baby seems dehydrated (see signs above)
Baby is under 3 months old with any diarrhea - call the same day
Diarrhea that contains blood or dark red mucus
Diarrhea alongside vomiting that's preventing your baby from keeping fluids down

When to go to the ER

Any signs of dehydration in a baby under 3 months
Sunken fontanelle, no tears, won't wake normally
Fever above 38°C (100.4°F) in a baby under 3 months
Bloody diarrhea that keeps coming
Baby is inconsolable and looks genuinely unwell

What actually helps

Keep breastfeeding. Breast milk has antibodies that actively help fight the infection causing the diarrhea, and it rehydrates at the same time. Don't stop.

Formula-fed babies: keep offering formula as normal. If baby is vomiting too, your doctor may recommend an oral rehydration solution like Pedialyte in small frequent amounts.

Do not use anti-diarrheal medications like Imodium - they're dangerous for babies. The old BRAT diet (bananas, rice, applesauce, toast) is also outdated - normal varied feeding helps the gut recover faster.

Know what's normal for your baby

The hardest part of spotting diarrhea is that you need a baseline to compare against. PipPoopie tracks your baby's poop patterns over time - so when something changes, you can see exactly how much it's changed and for how long. That context turns a worried call to your pediatrician into a useful one.