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Few things send parents into instant detective mode like an off-looking poop...especially if it’s one that looks wetter or smellier than usual. The tricky part: Normal baby poop can be pretty loose, especially for breastfed babies. So, when does “soft” cross into diarrhea—and what should you do next?

Here’s what to know about diarrhea in babies, including what it looks like, common causes, at-home relief tips, and the red flags that mean it’s time to get medical help.

What is diarrhea in babies?

Diarrhea is stool that’s waterier and/or happens more often than your baby’s usual pattern. This departure from normal is often the biggest clue. For many babies, especially those who are breastfed, everyday poop can be soft, runny, and frequent—and still be normal. What stands out with diarrhea is that stools suddenly become much looser (watery), much more frequent, or both.

What does diarrhea look like?

Because baby stool varies by age and feeding type, it helps to focus on consistency + frequency + your baby’s baseline:

  • Breastfed babies: Stools are often loose and may look mustard-yellow with small seed-like bits. That can be totally typical.
  • Formula-fed babies: Stools are often thicker—more like peanut butter—and may be yellow/tan.

With diarrhea, you’re more likely to see stool that’s very watery, may soak into the diaper like urine, and appears more times than usual across the day.

Signs of Diarrhea in Babies

  • Watery stools, sometimes leaking or “exploding” more than usual
  • A sudden jump in frequency (more stools than your baby typically has)
  • Mucus in the stool
  • A new or rapidly worsening diaper rash (diarrhea can irritate skin quickly)
  • Stool that looks abnormal in color—especially black, bloody, or white/clay-colored (these are red flags)

What causes diarrhea in babies?

Most of the time, diarrhea is short-lived and related to a temporary irritation in the digestive tract.

  • Viral infections are a top cause, including viruses that spread easily in families and childcare settings. Norovirus, for example, can cause vomiting and diarrhea and can lead to dehydration in young children.
  • Bacterial or parasitic infections are less common but can happen—particularly if diarrhea is severe, persistent, or accompanied by blood/mucus or high fever.

Other common triggers include:

  • Antibiotics. Antibiotics can disrupt the balance of gut bacteria and lead to diarrhea, even when the medication is necessary for treating an infection.
  • Diet changes. Starting solids, switching formulas, or introducing new foods can change stool patterns. Often this settles as baby’s system adapts, but if stools are watery and frequent, treat it like diarrhea and focus on hydration.
  • Food sensitivities/allergies or digestive conditions. These are less common, but they may be considered if diarrhea is recurrent, doesn’t improve, or is paired with poor weight gain or other symptoms. Persistent diarrhea deserves a call to your pediatrician.

How to Help a Baby With Diarrhea

When it comes to diarrhea relief, the big goal is preventing dehydration while keeping baby comfortable.

Keep fluids coming.

Babies can dehydrate faster than adults, so feeding and hydration are priority #1. In many cases you can continue your usual feeding routine:

  • Breastfed babies: Continue breastfeeding. Breastmilk provides fluid and nutrition and is generally well tolerated.
  • Formula-fed babies: Continue formula unless your pediatrician advises a change.

If your baby is also vomiting, smaller, more frequent feeds may be easier to keep down.

Consider an oral rehydration solution.

If diarrhea is frequent, very watery, or wet diapers are decreasing, your pediatrician may recommend an oral rehydration solution to help replace fluids and electrolytes in the right balance. Oral rehydration therapy is sometimes recommended for mild to moderate dehydration from gastroenteritis. Follow your pediatrician’s guidance on how much and how often—especially for young infants. Avoid sports drinks for babies; they don’t have the right electrolyte balance!

Be thoughtful with solids (if your baby already eats them).

If your baby is already on solids, you don’t necessarily need to stop foods altogether—but keep it simple and gentle while their gut recovers. Commonly tolerated options include bland starches and easy-to-digest foods. A key “skip” during diarrhea: juice. It can worsen diarrhea in some babies and toddlers.

Protect that diaper area early.

Diarrhea can irritate baby skin quickly, so don’t wait for redness to show up.

Gently clean the area (warm water and a soft cloth can be kinder than frequent wiping if skin is raw). Then, pat it dry before applying a thick barrier layer of zinc oxide paste or petroleum jelly).

Reduce spread if illness is the cause.

If your baby’s diarrhea is from a virus, it can spread easily through hands and surfaces. Norovirus, in particular, is highly contagious. Washing hands thoroughly and cleaning high-touch surfaces helps protect the rest of the household.

When to Seek Help for Diarrhea in Babies

Trust your instincts here. If your baby seems “off,” isn’t feeding well, or you’re worried about dehydration, it’s worth calling.

Call your pediatrician promptly if your baby:

  • Is 3 months old or younger and has diarrhea
  • Has a rectal temperature of 100.4°F (38°C) or higher
  • Has vomiting along with diarrhea
  • Seems unusually sleepy, difficult to comfort, or refuses feeds
  • Has signs of dehydration, such as a dry mouth, fewer tears, or significantly fewer wet diapers

Seek urgent medical care if you see:

  • Blood in the stool or black/tarry stool
  • White or clay-colored stool
  • Severe dehydration signs, such as very low urine output, extreme lethargy, or a sunken soft spot paired with concerning behavior changes

If you’re unsure what counts as “fewer wet diapers,” your pediatrician can help you interpret what’s normal for your baby’s age and feeding pattern—when in doubt, call.

How long does diarrhea in babies last?

Many viral stomach bugs improve within a few days, but the exact timeline varies by the virus and by your baby’s age. What matters most is the trend: Is your baby staying hydrated and gradually improving? If diarrhea is not improving, is worsening, or is paired with dehydration concerns, check in with your pediatrician.

More Diaper Deets:

 

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REFERENCES

  • American Academy of Pediatrics: Diarrhea in Babies
  • NIH National Library of Medicine: Diarrhea in Infants
  • American Academy of Pediatrics: Diaper Rash
  • Centers for Disease Control and Prevention: About Norovirus
  • Gastroenteritis in Children, American Family Physician, February 2019
  • American Academy of Pediatrics: Signs of Dehydration in Infants & Children
  • World Health Organization: Oral Rehydration Salts

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Disclaimer: The information on our site is NOT medical advice for any specific person or condition. It is only meant as general information. If you have any medical questions and concerns about your child or yourself, please contact your health provider.