Can Formula Cause Baby Constipation?

If you’re formula feeding, you probably spend a lot of time thinking about bottles, ounces…and poop. So, when your baby seems uncomfortable and the dirty diapers slow down, it’s natural to wonder: Is formula causing my baby’s constipation?

The short answer: Formula-fed babies do tend to have firmer, less frequent stools than breastfed babies, and some little ones are more prone to constipation than others. But most constipation can be eased with a few gentle tweaks—and knowing when it’s time to call the doctor.

Why does formula sometimes cause constipation?

First, a quick definition: Pediatric experts define constipation as bowel movements that are hard, dry, painful, or very difficult to pass, sometimes with fewer poops than usual. It’s not just about how often your baby poops—but what those poops are like and how your baby feels.

Here’s why formula may factor into a baby’s constipation:

The Way Formula Is Digested

Breastmilk tends to act like a natural gentle laxative and usually produces softer, more frequent stools. Formula is thicker and made from processed proteins that can be a bit harder for some babies to digest, which may lead to firmer stools.

The American Academy of Pediatrics (AAP) notes that formula-fed babies typically have at least one bowel movement most days, but going every one to two days can still be normal—as long as stools are soft and easy to pass.

Changes in Diet

Constipation often pops up when babies switch from breastmilk to formula, change formula types, or later when they start solids. These changes can temporarily slow the gut as it adjusts to new proteins, fats, and carbohydrates.

Hydration and Formula Mixing

When babies don’t get enough fluid, stools can become dry and hard. Under- or over-concentrating formula is risky: Mixing in too much powder can contribute to dehydration and constipation, while adding too much water can dilute nutrients and even cause dangerous electrolyte problems.

Underlying Cow’s Milk Protein Allergy

This is less common, but in some babies, constipation can be one of the signs of cow’s milk protein allergy, especially if it comes along with blood in the stool, eczema, vomiting, or poor growth.

Does iron in formula cause constipation?

Some parents worry that iron in formula causes constipation. The AAP specifically notes that the amount of iron in standard infant formula does not cause constipation, and recommends using iron-fortified formula for the first year.

Symptoms of Constipation in Formula-Fed Babies

Babies’ poop patterns are wildly variable (lucky you!). Still, these signs suggest constipation:

• Hard, dry, or pellet-like stools
• Straining, crying, or arching with bowel movements
• Infrequent poops plus hard consistency (for example, every few days and very firm)
• Bloated or firm belly
• Small streaks of blood on the stool or diaper from tiny anal fissures caused by straining

Some babies can go five to seven days between bowel movements and still be fine—as long as stools are soft and easy to pass, and your baby is feeding and growing well. If your baby seems content, is eating well, and poops are soft when they do happen, they may not actually be constipated!

How do you know if formula is causing constipation?

It can be tricky to tease out whether formula itself is causing constipation or it’s just a normal variation. A few clues:

• Timing: Did constipation begin soon after starting formula, switching brands, or changing from ready-to-feed to powder (or vice versa)?
• Stool changes: Did your baby’s poop go from soft/mushy to hard, dry, or infrequent around the same time as a formula change?
• Mixing issues: Double-check the scoop-to-water ratio on the can. Using more powder than recommended can lead to overly concentrated formula and harder stools.
• Other symptoms: If constipation comes with blood in the stool, vomiting, rash, or poor weight gain, your pediatrician may consider cow’s milk protein allergy or another medical issue.

If you suspect formula is contributing, don’t DIY big changes. Reach out to your pediatrician before switching formulas or altering how you mix bottles.

How to Give Your Baby Relief

The good news: Most constipation in formula-fed babies improves with simple, gentle steps.

Check the basics.

Confirm that you’re mixing your formula according to the instructions and make sure you’re offering feeds regularly. Babies who aren’t getting enough total fluid can develop drier stools. Your pediatrician can recommend a feeding schedule.

Ask about switching formula

Sometimes a different formula—such as one with partially hydrolyzed proteins or, if needed, a hypoallergenic formula—may result in softer stools for certain babies. Your pediatrician can guide you on whether a trial switch makes sense in your baby’s case and for how long to try it.

Use age-appropriate fluids (with your doctor’s okay).

For babies over about 1 month old who are constipated, some experts suggest that a small amount of extra water or 100% fruit juice may help soften stools by drawing water into the intestines. But never introduce water or juice without your healthcare provider’s guidance! And never water down formula beyond what your doctor recommends—this can be dangerous.

Try gentle movement and massage.

Simple, non-diet steps can also help move things along:

• “Bicycle” Baby’s legs while they’re lying on their back.
• Tummy massage: Gently rub their belly in a clockwise circle.
• Warm bath: This can relax your baby’s abdominal muscles and sphincter.

For older babies on solids…

If your baby is already eating solid foods, adding fiber-rich fruits and veggies (like pureed pears, prunes, peas, or beans) and making sure they’re drinking enough fluids can help prevent and treat constipation.

What not to do…

• Don’t concentrate formula or use home-made “extra-strong” bottles to try to “fill baby up”—this can cause serious dehydration and electrolyte imbalances.
• Don’t use enemas, suppositories, or over-the-counter laxatives in infants unless your pediatrician specifically recommends and doses them.

When to Seek Help About Formula and Constipation

Even when you’re doing everything “right,” some babies truly need medical evaluation and treatment. Call your pediatrician if:

• Your baby seems to be in significant pain with bowel movements
• Poops are consistently hard, dry, or pellet-like
• There is repeated blood in the stool
• Your baby isn’t feeding well, is vomiting, or seems unusually sleepy or irritable
• There’s persistent abdominal swelling or a very firm, tender belly
• Your newborn hasn’t passed meconium (their first dark stool) in the first 24 to 48 hours of life

These can be signs of more serious constipation or an underlying condition that needs prompt care.

Seek emergency help right away if your baby has:

• Green (bilious) vomiting
• A very swollen, tense belly
• Refusal to feed plus lethargy
• Blood in the stool plus fever or severe distress

The Bottom Line

Constipation with formula can be stressful—but usually fixable! And remember: You never have to troubleshoot formula and constipation alone. Your pediatrician is there to help your little one get back to comfy, easy poops…and to help you worry a whole lot less about what’s in those diapers.

More on Caring for Your Baby:

• Everything You Need to Know About Feeding a Baby
• How to Make and Store Formula
• Signs Your Baby Is Hungry
• Paced Bottle Feeding: How to Do It—and Why You Should

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.