What Causes Reflux in Babies? Understanding the Reasons Behind Infant Reflux
By Dr. Jennifer Harris | Crying, Colic, and Beyond
If your baby is struggling with reflux, you've probably spent hours trying to figure out why. Is it something in their formula? Something you've eaten while breastfeeding? An allergy? An immature digestive system?
For many parents, the search for answers begins with a suspected cow's milk protein allergy (CMPA). And while allergies can certainly contribute to reflux symptoms, they are far from the only possible explanation.
In fact, infant reflux is often influenced by several different factors, and understanding those factors is an important part of finding the right approach to treatment.
Let's explore what actually causes reflux in babies, why some babies experience much more discomfort than others, and why simply changing formulas or eliminating dairy isn't always the answer.
First, What Exactly Is Infant Reflux?
Reflux occurs when stomach contents flow backward into the esophagus, the tube connecting the mouth to the stomach.
At the bottom of the esophagus is a ring of muscle called the lower esophageal sphincter (LES). Its job is to open to allow food into the stomach and then close to help prevent stomach contents from flowing back upward. In babies, this mechanism is still developing. The LES can relax temporarily, allowing milk and stomach contents to travel back into the esophagus.This is called gastroesophageal reflux (GER), and it's incredibly common during infancy.
For many babies, reflux causes little more than occasional spit-up. They feed comfortably, gain weight appropriately, and are otherwise happy and healthy.
However, when reflux causes troublesome symptoms or complications, it may be classified as gastroesophageal reflux disease (GERD).
The important distinction isn't simply how much a baby spits up. It's whether reflux is causing problems.
Some babies spit up frequently without discomfort, while others may experience significant feeding difficulties or distress with very little visible regurgitation.
And that's where understanding the possible causes becomes particularly important.
1. An Immature Lower Esophageal Sphincter
One of the most common reasons babies experience reflux is simply that their digestive systems are still developing.
The lower esophageal sphincter is responsible for helping keep stomach contents where they belong. In young infants, temporary relaxations of this muscle occur frequently.
When the sphincter relaxes, stomach contents can move back into the esophagus.
Several characteristics of infancy make this more likely:
Babies consume an entirely or predominantly liquid diet.
Their stomachs are relatively small.
They consume frequent feeds that are large relative to their body size.
They spend much of their time lying down.
The mechanisms that help prevent reflux are still maturing.
As babies grow, spend more time upright while awake, and begin eating solid foods, reflux often becomes less frequent. However, while this explains why reflux is so common, it doesn't necessarily explain why some babies experience significant pain, feeding refusal, or other concerning symptoms.
Normal developmental reflux and reflux disease are not necessarily the same thing.
A baby's age may explain why reflux is happening, but it shouldn't automatically be used to dismiss persistent distress or feeding difficulties.
2. Cow's Milk Protein Allergy (CMPA) and Other Food Allergies
Cow's milk protein allergy is an important consideration when evaluating a baby with reflux symptoms.
In some infants, an immune reaction to cow's milk proteins can cause gastrointestinal symptoms, including vomiting, regurgitation, and feeding discomfort. These symptoms can overlap considerably with those of GERD, making it difficult to distinguish between the two based on symptoms alone.
Babies with CMPA may also experience:
Eczema or other skin symptoms
Blood or mucus in their stools
Diarrhea or constipation
Abdominal discomfort
Feeding difficulties
Poor weight gain in more severe cases
However, not every baby with CMPA has visible blood in their stool, and not every baby with reflux has an allergy. Likewise, it's also possible for reflux and CMPA to coexist.
When CMPA is suspected, a clinician may recommend a carefully planned trial of cow's milk protein elimination, followed by an appropriate reintroduction or challenge to help confirm the diagnosis.
But here's something I want parents to understand: changing formulas repeatedly without a clear reason isn't necessarily going to resolve reflux.
If the primary issue is related to esophageal function, feeding mechanics, or another gastrointestinal condition, eliminating dairy may have little effect. And, if symptoms persist despite an appropriate allergy management plan, it's important to consider what else may be contributing.
3. Delayed Gastric Emptying
Another possible contributor to reflux is delayed gastric emptying.
Normally, after milk enters the stomach, it gradually moves into the small intestine for further digestion. In some babies, this process happens more slowly than expected.
When stomach contents remain in the stomach for longer, there may be more opportunity for reflux to occur. Depending on the underlying issue, a baby might experience:
Frequent regurgitation or vomiting
Discomfort after feeds
Early fullness
Difficulty tolerating larger feeding volumes
Persistent symptoms despite other interventions
However, these symptoms are not specific to delayed gastric emptying, and they do not establish the diagnosis. Importantly, not every baby with reflux has delayed gastric emptying, and not every baby who struggles with feeding volumes has a motility disorder. When symptoms are persistent or unusually severe, a pediatric specialist may consider whether further evaluation of gastrointestinal motility is appropriate.
4. Feeding Volumes, Feeding Mechanics, and Swallowing Difficulties
Sometimes, factors surrounding feeding can contribute to reflux or produce symptoms that resemble it.
For example, feeding volumes that exceed what a baby's stomach can comfortably accommodate may increase regurgitation. Other factors worth evaluating include:
Very fast bottle flow
Difficulty coordinating sucking, swallowing, and breathing
Fast maternal milk flow or oversupply during breastfeeding
Feeding positions and techniques
Swallowing difficulties or dysphagia
These issues don't necessarily cause GERD, but they can contribute to discomfort, coughing, gulping, or feeding struggles.
It's also important to distinguish reflux from swallowing dysfunction. A baby who coughs, chokes, or struggles to coordinate breathing during feeds may need an assessment for dysphagia or aspiration rather than simply another reflux treatment.
This is why a detailed feeding history can be so valuable.
Sometimes the most important clues aren't just what happens after a feed, but what happens during the feed itself.
5. Prematurity and Digestive Development
Babies born prematurely can be particularly vulnerable to feeding and gastrointestinal difficulties.
If your baby was born pre-term, their digestive systems, swallowing coordination, and mechanisms that help prevent reflux may be less mature than those of full-term infants.
Premature babies may also have additional medical or developmental factors that affect feeding tolerance. While reflux is common in both premature and full-term babies, prematurity is associated with a greater likelihood of GERD and can make assessment more complex.
It's particularly important not to assume that every episode of crying, arching, breathing difficulty, or feeding intolerance in a premature baby is caused by reflux. These symptoms may have other explanations that require careful evaluation and any treatment decisions, particularly those involving medication, should take a baby's age, developmental maturity, medical history, and individual risks into account.
6. Anatomical and Other Medical Conditions
Less commonly, persistent reflux symptoms may be associated with an underlying anatomical or medical condition.
Examples include:
Hiatal hernia, which can affect the normal barrier between the stomach and esophagus
Certain congenital abnormalities of the gastrointestinal tract
Neurological conditions that affect swallowing or gastrointestinal function
Previous surgery involving the esophagus
Other conditions affecting gastrointestinal motility
Some conditions, such as pyloric stenosis or intestinal obstruction, can also cause vomiting that may initially be mistaken for reflux. These conditions are not typical explanations for ordinary infant spit-up, but they highlight why persistent, severe, or unusual symptoms deserve appropriate medical assessment.
7. Esophageal Sensitivity and Inflammation
One question parents frequently ask is:
Why does one baby spit up constantly and seem perfectly happy, while another appears to be in pain even though they rarely spit up?
Part of the answer may involve how the esophagus responds to reflux. When stomach contents enter the esophagus, they may contain acid, digestive enzymes, or other material that can irritate the esophageal lining.
In some babies with GERD, repeated exposure can contribute to inflammation, known as esophagitis. Others may experience discomfort related to esophageal sensitivity, even without obvious injury. This helps explain why the amount of visible spit-up doesn't always correspond to the severity of symptoms.
It's also important to understand that not all reflux is acidic. Acid-suppressing medications reduce stomach acidity, but they don't necessarily prevent stomach contents from moving backward into the esophagus. This is one reason a baby may continue to regurgitate despite receiving reflux medication and it also helps explain why acid suppression isn't appropriate or effective for every baby with reflux-like symptoms.
Can More Than One Factor Be Contributing?
Absolutely.
In fact, this is one of the most important things to understand about infant reflux. A baby might have a naturally immature reflux barrier alongside CMPA. Another might have reflux combined with swallowing difficulties. Another who has experienced repeated painful feeds may begin developing negative associations with feeding, even after the original source of discomfort has improved.
This last point is particularly important.
When Reflux Leads to Feeding Aversion
When feeding repeatedly causes discomfort, some babies begin to associate eating with unpleasant experiences.
Over time, this can contribute to behaviors such as:
Turning away from the breast or bottle
Crying when offered a feed
Arching, pushing away, or becoming distressed during feeding
Taking only small amounts while awake
Feeding more readily when sleepy or drowsy
These behaviors don't automatically mean a baby has feeding aversion. Pain, swallowing difficulties, flow problems, and other conditions can produce similar signs.
However, when negative feeding associations do develop, treating the original medical issue may not immediately resolve the feeding difficulties. The baby may also need support to rebuild a comfortable, positive relationship with feeding. This is why addressing reflux isn't always as simple as choosing the right formula or medication.
Why Isn't My Baby's Reflux Improving?
If your baby has already tried formula changes, dietary elimination, or medication without meaningful improvement, it can be incredibly frustrating.
It's important to remember that a lack of improvement doesn't necessarily mean there are no further options. Instead, it's an opportunity to revisit the original assumptions.
Some of the questions worth considering include:
Was reflux actually the primary cause of the symptoms?
Could an allergy or another gastrointestinal condition be contributing?
Are there feeding or swallowing difficulties?
If medication is being used, is it appropriate for the suspected condition, and has its effectiveness been reassessed?
Could feeding aversion now be playing a role?
Are there symptoms that warrant further investigation?
When reflux treatment isn't producing the expected results, the answer isn't always to add another medication or switch formulas again. Sometimes the most valuable next step is taking a closer look at why the baby is struggling in the first place.
When Should Parents Seek Medical Advice?
While uncomplicated reflux is extremely common, certain symptoms deserve further evaluation.
Speak with your baby's pediatrician if your baby experiences persistent feeding refusal, apparent pain with feeds, recurrent vomiting, difficulty gaining weight, or symptoms that aren't improving.
Seek urgent medical attention for:
Green (bilious) vomit
Blood in vomit
Repeated forceful or projectile vomiting, particularly in a young infant
Breathing difficulties or episodes of turning blue
Signs of dehydration
Marked lethargy or an unusually unwell appearance
These symptoms should not simply be attributed to reflux. And remember: For sleep, babies should always be placed on their backs on a firm, flat sleep surface, even when they have reflux. Inclined sleep products and sleep positioners are not recommended.
Understanding the Cause Is an Important Part of Finding Relief
If there's one thing I want parents to take away from this article, it's this:
Reflux is not a single condition with a single cause or a one-size-fits-all solution.
For some babies, reflux is a normal part of development that improves with time. For others, symptoms may be influenced by allergies, gastrointestinal function, feeding difficulties, esophageal inflammation, or a combination of factors. And sometimes, what initially appears to be reflux turns out to have another explanation entirely.
At Crying, Colic, and Beyond, our approach is to look at the whole baby: their symptoms, feeding history, growth, medical background, previous treatments, and response to those treatments.
When a baby is struggling, we believe parents deserve more than an assumption that they'll simply grow out of it. They deserve a thoughtful assessment, an individualized plan, and support in understanding what may be happening.
Need Help Understanding Your Baby's Reflux?
If your baby is experiencing persistent reflux symptoms, feeding difficulties, or discomfort despite previous treatment, our team may be able to help.
At Crying, Colic, and Beyond, Dr. Jennifer Harris provides specialized telehealth consultations for families navigating infant reflux, GERD, cow's milk protein allergy, and feeding aversion.
Our consultations focus on understanding your baby's individual history, identifying potential contributing factors, and developing a personalized management plan.
About Dr. Jennifer Harris
Dr. Jennifer Harris is a board-certified pediatrician with over a decade of focused experience supporting infants and families affected by reflux, GERD, food allergies, and feeding difficulties.
Through Crying, Colic, and Beyond, she works with families to provide individualized, evidence-informed care that considers the full picture of an infant's symptoms and development.
Medical disclaimer: This article is for educational purposes only and is not a substitute for individualized medical advice, diagnosis, or treatment. Always consult your child's healthcare professional regarding symptoms, feeding concerns, or medication decisions.
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