Milk Allergy

Milk Allergy

Milk Allergy

Vomiting, diarrhea, a rash, breathing problems, and lack of weight gain may be signs that your baby has a food allergy. Read about the symptoms, the foods most likely to cause an allergic reaction in babies and young children, and how food allergies are diagnosed and treated.

What is an allergen?

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, almost anything can contain protein and thus has the potential to be an allergen for someone. 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, cows' or goats' milk or soy infant formula, are the most common forms of food allergy experienced by babies. 


Formula-fed babies

Milk allergy affects about 1 in 50 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.  

Human babies are biophysiologically programed 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. Therefore formula-fed babies are at increased risk of milk protein allergy compared to breastfed babies.

Breastfed babies

Babies are never allergic to their mother’s milk.  But exclusively breast-fed babies can be sensitized to cows' milk protein (CMP) consumed their mother and transferred through her milk. The prevalence of CMA in exclusively breast-fed babies is believed to be around 0.37 percent. In other words, less than 1:250 exclusively breastfed babies are affected. It is rare because there are so few CMP antigens present in breast-milk. Also breast-milk contains immunological properties that reduce the risk of allergy development. Studies show that breastfeeding reduces the 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.


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 

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.


  • failure to gain weight or weight loss.


  • 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 to develop within 45 minutes of exposure to cows’ milk proteins. The reaction is either a measles-like rash or hives, facial swelling. The respiratory system can be affected in this group, causing wheezing or sneezing or itchy, red eyes and anaphylactic shock. Allergy tests (skin prick tests or RAST blood tests) will often provide positive test results for this group.

Slow reaction

Symptoms such as vomiting, diarrhea and blotchy rash can develop between 45 minutes and 20 hours after exposure to cows’ milk proteins. Allergy tests (skin prick tests or RAST blood tests) are only positive in about 1 in 3 children in this group.

Late Reaction

Symptoms, which can include vomiting, diarrhea, eczema and asthma, can develop up to 20 hours after exposure to cows’ milk proteins. Only 1 in 5 children with delayed reactions show a positive skin prick test.


While diagnostic tests are available they are generally unreliable for babies under the age of 12 months. Confirmation of milk allergy in babies is usually based on an Elimination and Challenge’ procedure.

Elimination and Challenge

Milk allergy and intolerance can be diagnosed by removing milk (and milk products) from the diet for a period of time to see if symptoms disappear, and then reintroducing it again for one feed to see if symptoms return. 

IMPORTANT: Elimination and re-introduction of milk and its products should only be undertaken with medical advice, particularly in cases with severe symptoms.

Diagnostic tests

  • Atopy Patch Test: This is an allergy test where a special "patch" of test material is placed upon the skin and the allergy response tested.
  • Skin prick test (SPT): This is an allergy test where an allergen is placed and pricked onto the skin and any allergy response measured. This test can be carried out safely and reliably in children as young as three months of age.
  • Radioallergosorbent Test (CAP/RAST):  CAP/RAST blood tests measure antibodies to proteins called IgE (Immunoglobulin E). It also tests for milk proteins as whole or individual fractions of milk (casein, whey, and beta-lactoglobulin).


The treatment for different types of allergies depends on whether the allergen can be avoided or not. Avoidance, which prevents symptoms in a sensitive person, is the best option but this is not always possible, particularly in the case of airborne allergens.

Formula-fed baby

Treatment involves switching baby to one of the following formulas:

  • soy-protein infant formula;
  • extensively hydrolyzed infant formula (e.g. Nutramigen, Progestimil, Alimentum, Alfare and Pepti-Junior);
  • or amino-acid infant formula (e.g. Elecare, Neocate). (See Infant formula for more).

Breast-fed baby

Treatment involves complete avoidance of cows' milk proteins. Because many babies can be allergic to a number of different foods, it may be necessary to consult with dietician for guidance on dietary restrictions.

When to see the doctor 

If your child has any of the symptoms above or if you suspect your child may have a milk or food allergy, see your child's doctor. Diagnosis is a difficult enough process even for an expert. Trying to work it out the best method of dealing with a cow' milk protein allergy or intolerance on your own would be virtually impossible.

Written by Rowena Bennett

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