Milk allergy is one of the most common food allergies among children, with around 3% to 6% of infants and young children developing the allergy by the time they are a few months old. Children usually outgrow this allergy by the age of five, thus it is very uncommon among older children and adults.

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Milk allergy is caused by the immune system having an abnormal reaction to milk and products that contain milk. The most common culprit is the proteins found in cow’s milk, although an allergic response may also be triggered by consuming milk from other mammals such as sheep, goats or buffalo.

Milk allergy should be distinguished from lactose intolerance, which is not an allergic condition and does not involve the immune system. Lactose intolerance is the inability to digest lactose (the sugar present in milk) due to a lack of the enzyme lactase which breaks the lactose down. Lactose intolerance causes different symptoms to milk allergy and may lead to digestive problems after the consumption of milk.

Cause of milk allergy

The immune system mistakes the proteins in milk for a harmful substance or allergen, which triggers the production of immunoglobulin E (IgE) antibodies to fight off the allergen. The next time a person ingests milk proteins, the IgE antibodies identify them and flag them up to the immune system.

This in turn causes the releases or histamine and other chemicals that bring on the symptoms of an allergic reaction. The two main proteins contained in cow’s milk that trigger this reaction are casein (found in the curd of milk) and whey (found in the liquid part of milk).

Symptoms

An allergic reaction to milk usually occurs within minutes of exposure with symptoms ranging from mild to severe. Symptoms may include wheezing, digestive problems, hives, vomiting and wheezing. In some cases, the allergy can trigger a more severe reaction called anaphylaxis, which can be life threatening.

The signs and symptoms of anaphylaxis may include constricted airways, a swollen throat making it difficult to breathe, a marked fall in blood pressure, facial flushing and itching. A person experiencing this reaction requires emergency treatment with a shot of epinephrine, the only drug that can reverse these symptoms.

Risk factors

Certain factors increase the likelihood of someone developing a milk allergy and these include the following:

• Existing allergies – many children who develop a milk allergy also have other allergies
• Atopic dermatitis – a chronic skin inflammation
• A family history of allergies such as asthma, hay fever or eczema
• Age – young children are more likely to develop a milk allergy than older children or adolescents. As a child grows up and their digestive system matures, the likelihood of them developing a milk allergy is reduced

Diagnosis

If a doctor suspects that a child has a milk allergy, they will ask questions about the child’s signs and symptoms, perform a physical assessment and ask that a diary is kept detailing what the child eats. They may ask that milk is eliminated from the diet and then added back to the diet to see if it causes a reaction.

The doctor may also recommend a skin prick test, where a small amount of milk protein is applied to the skin to see if a hive develops and/or a blood test to check the amount of IgE antibodies in the blood.

Differential diagnoses include various metabolic disorders, coeliac disease and other enteropathies, insufficiency of the pancreas, non‐immunological adverse reactions to certain foods (such as secondary lactose intolerance or fructose malabsorption), allergic tendencies to other food allergens, as well as certain infections.

Management

The main approach to treating this allergy is to avoid consuming milk or milk products, although this can be difficult as milk is a common ingredient in so many foods. If a person needs to avoid consuming cow’s milk, they should remember that the milk is present in many products including the following:

• Milk powder
• Butter
• Cheese
• Milk drinks
• Ice cream
• Margarine
• Yoghurt
• Cream

Food items for which the following ingredients are listed may also contain cow’s milk or cow milk products:

• Milk solids
• Skimmed milk
• Casein
• Hydrolyzed casein
• Non-fat milk
• Lactose
• Milk sugar solids
• Whey
• Whey syrup sweetener

The following processed foods may also contain milk:

• Soup
• Pasta and pizza
• Cereal
• Instant mash
• Baby foods
• Processed meats such as sausages
• Cakes and biscuits
• Crackers
• Custard
• Batters and pancakes
• Sauces
• Gravies
• Crisps
• Chocolate
• Ready-made meals

If a child does accidentally consume milk, antihistamines can be taken to help reduce the symptoms of an allergic reaction and relieve discomfort. If a child is at risk of developing anaphylaxis, they may be prescribed injectable epinephrine, which will need to be available at all times.