Milk Allergy in Babies: Signs, Symptoms, and What to Know

Cow’s milk allergy is one of the more common food allergies in infancy, but it is also frequently misunderstood. Many symptoms attributed to milk allergy overlap with normal infant behaviour or other feeding-related issues. Understanding the possible signs, how milk allergy is assessed, and its limitations can help parents make informed decisions and avoid unnecessary dietary restriction.

What is an allergen and why do allergies develop?

An allergen is the substance that is responsible for triggering an allergic reaction. Allergens contain protein. Protein is not simply something we eat. Plants, animals and insects are made up of the building blocks of protein. Therefore, many substances that contain protein have the potential to act as allergens for some people. The most common allergens are dust mite excretion, mold and pet dander, but protein in certain foods can also be allergens for some people.  

Milk protein, including cow’s milk protein, and soy are among the most common food allergens affecting babies.

Incidence Of Milk Allergies in Babies

Formula-fed babies

It is estimated that milk allergy affects about 1 in 50 formula-fed babies. Milk is the most common cause of food allergy. Cows’ milk allergy (CMA) is more prevalent in formula-fed babies because the majority of infant formulas are based on cows’ milk. However, non-human protein such as goats' milk formula and soy infant formula can also trigger an allergic reaction in sensitive babies. 

Babies are biophysiologically programmed to consume human milk, not milk from other species such as cows’ or goats', nor “milk” made from soybeans. Infant formula is "humanized” to make it more like breastmilk but manufactured baby milk cannot replicate breastmilk. As a result, formula-fed babies may have a higher risk of milk protein allergy compared to breastfed babies.

Breastfed babies

Babies are not allergic to their mother’s milk itself. However, exclusively breastfed babies can be sensitized to cow’s milk protein (CMP) consumed by their mother and transferred through her milk.

CMA is uncommon in exclusively breastfed babies, with estimates suggesting it affects fewer than 1 in 250 infants. This is thought to be rare because there are very small amounts of CMP antigens present in breast milk. Breast milk also contains immunological properties that reduce the risk of allergy development. Studies show that breastfeeding is associated with a reduced incidence of eczema and allergic food reactions in babies.

Inherited traits

A baby is more likely to develop milk or food allergy if blood relatives also experience allergies such as eczema, asthma, hay fever or food allergy.

Medications

Antacids, acid suppressing medication and antibiotics have been shown to increase the risk food allergies and intolerance in adults. (It is unethicial to conduct similar clinical trials on babies. Therefore we can only assume these medications will have the same effect on babies, who are more susceptible to food allergies compared to adults due to immaturity of their digestive tract and immune system). Medications that prevent of minimize the production of stomach acid, which is necessary for the breakdown of food proteins in the stomach, increase the risk of food allergy.[1] Medications that deplete the number of good bacteria in the intestinal tract, which includes both antacids and antibiotics, also increase the risk of food allergy.[2] 

Other causes

The exact reason why the incidence food allergies have increased significantly in babies and children over the past 2 decades are largely unknown.

Fortunately, approximately half of the children affected by a milk allergy will outgrow the problem by 1 to 2 years of age, and approximately three quarters of children will have outgrown it by the time they're 3 or 4 years old. So they can then go back to drinking milk and eating dairy foods the same as other children.

Signs and symptoms of milk allergy in babies

Histamine, which the body produces in response to exposure to the allergen, is responsible for the allergic symptoms. Histamine circulating in the blood stream has the potential to affect many different organ systems including the gastro-intestinal tract but also the skin, nose, throat and lungs. Sometimes the symptoms will be primarily limited to one body system, but often multiple body systems are affected.

Skin reactions

• rash around the mouth;
• swelling of lips, mouth, tongue, face or throat;
• eczema behind ears and in body creases, such as neck and elbows;
• scaly skin on cheeks;
• dry skin or skin cracks e.g. bottom of the ear lobe, corner of the eye;
• persistent diaper rash;
• hives;
• itchy red rash;
• allergic ‘shiners’ (black eyes);
• watery or itchy eyes.

Nose, throat and lungs reactions

• runny nose (clear, watery);
• nasal congestion - stuffy or blocked nose;
• sneezing;
• wheezing;
• itchy nose, throat or palate (roof of mouth);
• coughing;
• wheezing or shortness of breath.

Stomach and bowel reactions

• abdominal pain and bloating;
• cramps;
• vomiting;
• excessive gassiness;
• diarrhea (loose runny stools), mucous or blood in motions.

Growth

• failure to gain weight or weight loss.

Behaviour

• irritability;
• poor sleep;
• fussy feeding behaviour. 

Note: Not all reactions to milk are due to milk allergy. See ‘Milk allergy versus intolerance’.

Onset of symptoms

Reactions can occur immediately or up to several days after exposure to cows’ milk proteins. The timing of symptoms can help to differentiate between a milk allergy and intolerance. 

Early reaction

Symptoms can begin within minutes to around 45 minutes of exposure to cow’s milk protein. Reactions may include hives or a widespread red rash, facial swelling, and involvement of the respiratory system, such as wheezing, sneezing, or itchy, red eyes. In rare cases, a severe allergic reaction (anaphylaxis) can occur.

In this group, allergy testing such as skin prick testing or serum specific IgE (RAST) blood tests is often positive and may support the diagnosis when interpreted alongside the clinical history.

Delayed reaction

Symptoms such as vomiting, diarrhea, changes in stool pattern, and skin symptoms including rash or eczema may develop several hours to days after exposure to cow’s milk protein. These reactions are commonly referred to as non-IgE–mediated milk allergy.

In this group, standard allergy testing such as skin prick tests or serum specific IgE (RAST) blood tests is often negative and does not reliably exclude milk allergy. Only a minority of babies with delayed reactions show positive test results, which is why diagnosis relies more heavily on clinical history and response to dietary elimination and reintroduction.

Why milk allergy is often misdiagnosed in babies

Many of the symptoms commonly attributed to milk allergy are also seen in healthy babies or in babies with feeding-related or gastrointestinal immaturity. As a result, cow’s milk allergy is frequently suspected in babies who do not have a true allergy.

Symptoms such as unsettled behavior, frequent crying, reflux-like symptoms, gas, or changes in stool pattern are common in infancy and are not specific to allergy. When these symptoms occur in isolation, particularly in a thriving baby with good growth, milk allergy is less likely.

Misdiagnosis can lead to unnecessary dietary restriction, repeated formula changes, or maternal elimination diets, which may increase feeding stress and, in some cases, contribute to premature cessation of breastfeeding. For this reason, careful assessment and consideration of alternative explanations are important before concluding that milk allergy is the cause of a baby’s symptoms.

Diagnosis

There is no single test that can reliably diagnose milk allergy in babies. Assessment is based on symptom patterns, the timing of symptoms in relation to milk exposure, and a baby’s response to elimination and reintroduction. Allergy tests may support assessment in babies with immediate reactions, but they are often unhelpful in delayed reactions and should not be relied upon alone.

Reviewing your baby’s symptoms and history

A health professional will consider:

• When symptoms first appeared

• How soon symptoms occur after milk exposure

• Whether symptoms improve when milk protein is removed

• Any history of eczema, reflux-like symptoms, or allergic conditions in the family

Keeping a symptom record

A simple symptom record can be very helpful in identifying patterns and understanding whether milk protein is a likely trigger. This does not need to be detailed or perfect. Useful information includes:

• What your baby was fed

• When symptoms appeared

• How long symptoms lasted

• Anything that seemed to improve or worsen symptoms

This information helps guide decisions about whether further assessment, dietary changes, or medical review are appropriate.

Elimination and reintroduction

Milk allergy and intolerance may be assessed by removing milk and milk-containing products from the diet for a period of time to observe whether symptoms improve, followed by cautious reintroduction to see if symptoms return.

Important: Elimination and reintroduction of milk and its products should only be undertaken with medical guidance, particularly in babies with severe symptoms or a history of immediate reactions.

Diagnostic tests

• Skin prick testing (SPT):
  A test in which small amounts of allergen are introduced into the skin to assess for an IgE-mediated allergic response. This test can be performed in infants, but results must be interpreted in the context of symptoms.

• Serum specific IgE blood tests (previously referred to as RAST):
  These tests measure IgE antibodies to milk proteins, including components such as casein and whey. Positive results support IgE-mediated allergy but do not confirm clinical allergy on their own.

Treatment

Treatment for allergies depends on whether the allergen can be avoided. Avoidance is the most effective way to prevent symptoms in a sensitive individual; however, this is not always possible, particularly in the case of airborne allergens.

Formula-fed baby

Treatment typically involves switching the baby to one of the following formulas, under medical guidance:

• Soy-protein infant formula

• Extensively hydrolyzed infant formula
  (e.g. Nutramigen, Progestimil, Alimentum, Alfare, Pepti-Junior)

• Amino acid–based infant formula
  (e.g. EleCare, Neocate)

 (See Infant formula for more).

Breastfed baby

Management usually involves removing cow’s milk protein from the breastfeeding mother’s diet. Because some babies may react to more than one food protein, dietary changes should be guided carefully. Consulting with a dietitian can help ensure nutritional needs are met while avoiding unnecessary or overly restrictive elimination.

When to see the doctor

If your baby has any of the symptoms described above, or if you suspect they may have a milk or other food allergy, it is important to seek medical advice. Diagnosing food allergy in babies can be challenging, even for experienced health professionals, as symptoms often overlap with other common infant conditions.

Trying to determine the cause of symptoms or manage a suspected cow’s milk protein allergy or intolerance without guidance can lead to unnecessary dietary restriction or missed diagnoses. Medical assessment helps ensure the safest and most appropriate approach for your baby.

What to do if anaphylaxis occurs

Anaphylaxis is a rare but severe allergic reaction that can occur suddenly and requires urgent medical attention. Symptoms may include:

• Difficulty breathing, swelling of the lips or face, persistent coughing or wheezing, sudden pallor or floppiness, or collapse.

If you suspect your baby is experiencing an anaphylactic reaction:

• Call emergency services immediately

• Do not delay seeking help

• If an adrenaline auto-injector has been prescribed, use it as directed while waiting for emergency assistance

Any baby who has experienced a severe allergic reaction should be urgently reviewed by a medical professional and referred for specialist allergy assessment.

Written by Rowena Bennett

About Rowena

Rowena Bennett (RN, RM, CHN, MHN, IBCLC) is a leading infant-feeding and sleep specialist and author of several books on infant feeding and behaviour, including the widely acclaimed “Your Baby’s Bottle-Feeding Aversion: Reasons & Solutions". With over three decades of clinical experience across child health, midwifery, mental health, and lactation, she has helped thousands of families worldwide understand and resolve complex feeding challenges through her evidence-based, baby-led approaches.

© Copyright www.babycareadvice.com 2026. All rights reserved. Permission from author must be obtained to copy or reproduce any part of this article.