Definition

Cow's milk allergy is one of the most common allergies. While it shares some symptoms with lactose intolerance, it is a distinct condition. Lactose intolerance typically arises when someone lacks enough lactase enzyme to digest or absorb lactose, the main carbohydrate in milk.

In contrast, cow's milk allergy stems from an abnormal immune response in the body. This reaction occurs when the immune system identifies specific proteins in milk as foreign substances. When immune receptors bind to these milk proteins, it triggers a chemical reaction, releasing immune mediators and causing inflammation, which manifests as milk allergy symptoms.

Most cow's milk allergy cases occur in infancy and tend to improve with age, usually around 6 years old. Children allergic to cow's milk typically react to casein and whey, the two main proteins in milk.

Causes

Individuals with cow's milk allergy experience symptoms when their immune system reacts to proteins found in milk. There are two main protein components in milk that can trigger cow's milk allergy reactions:

• Casein: This protein forms when milk spoils and solidifies into clumps. Casein is present in dairy products like cheese and yogurt. It accounts for about 80% of the protein in milk and gives milk its white color.
• Whey: Whey is a liquid by-product that forms when casein starts to solidify. It contributes to about 20% of the protein in milk.

When your immune system encounters one or both of these proteins again, possibly after the first exposure, it identifies them as antigens. As a result, your body generates immunoglobulin E (IgE) antibodies against the milk protein. The production of IgE antibodies triggers the release of various chemical mediators like histamine, leading to allergic reactions.

Risk factor

Some risk factors that may increase the likelihood of someone experiencing or having a cow's milk allergy include:

• Age

Researchers estimate that about 7% of newborns under 1 year old have a cow's milk allergy.

• Family history

If your family has a cow's milk allergy history, your likelihood of having a cow's milk allergy may triple.

• Pets at home

Some studies suggest that having pets at home may increase the risk of allergy due to sensitivity to pet dander.

• Short breastfeeding period

Babies breastfed for a shorter period than the normal breastfeeding duration may have a higher likelihood of having a cow's milk allergy. However, some research indicates a decreased risk of cow's milk allergy in babies who continue to consume breast milk.

• Other allergies

Children with a history of other forms of allergy, such as eczema and asthma, are at an increased risk of developing a cow's milk allergy.

• Introduction of food before 4 months of age

Babies who consume food before 4 months of age have a higher risk of allergies compared to babies who only consume breast milk until 6 months of age or older.

Symptoms

Symptoms of cow milk allergy can manifest minutes to hours after consuming milk and may vary from individual to individual, regardless of age. Some individuals may experience moderate reactions, while others may have more severe responses. Immediate symptoms occurring within an hour of milk consumption can include:

• Hives and rashes
• Sneezing
• Itchy or tingling skin around the mouth or lips
• Swelling of the lips, tongue, or throat
• Coughing or shortness of breath
• Vomiting
• Anaphylaxis, a severe and potentially life-threatening allergic reaction

If anaphylaxis occurs, immediate medical attention is crucial. Contact the emergency department promptly.

Delayed symptoms may include:

• Diarrhea
• Blood in stools
• Abdominal cramps
• Colic (in infants)

Diagnosis

If you experience symptoms of cow milk allergy, it's essential to inform your doctor. Your doctor may recommend conducting allergy tests to confirm the diagnosis. Some tests that can help diagnose cow milk allergies include:

• Blood test

Your doctor will draw a blood sample from your blood vessels during a blood test. The sample will be taken to the laboratory, where it will be exposed to cow's milk protein to measure the levels of IgE antibodies produced. Results from this test may take a week or more to be available.

• Skin prick test

This test involves exposing your body to a small amount of cow's milk protein. The doctor will clean the test area on your skin and then prick it with a needle (lancet) containing cow's milk protein. Alternatively, the doctor may apply cow's milk protein fluid to your skin and then prick it with the lancet. Positive and negative controls, typically containing histamine and saline solution, respectively, may also be used. After the test, any changes in skin color or reactions will be observed.

• Graded oral challenge

The doctor may recommend a food challenge test if your allergy history and test results do not align. During this test, you will consume milk in small amounts while the doctor observes for any reactions. More amounts of milk may be consumed to assess your body's response. This test typically lasts up to 4 hours.

• Specific serum IgE

This test measures the levels of IgE in your blood, which can trigger reactions upon contact with cow's milk protein. While this test can estimate potential reactions, it may yield false positives and is insufficient for a diagnosis.

Management

If you have a milk allergy, avoiding consuming milk and its derivatives is the most effective prevention for allergic reactions. Always check food labels to ensure that your foods or drinks do not contain milk ingredients.

Some children may outgrow their milk allergy as they grow older. If your child does not show any improvement in allergic reactions over time, discuss with your doctor the possibility of desensitization treatment, such as oral immunotherapy. Additionally, your doctor may prescribe an epinephrine auto-injector in case of an anaphylactic reaction.

Complications

Serious cow milk allergy complications primarily stem from malabsorption, which can result in iron deficiency anemia and impaired growth. While rare, anaphylaxis remains a severe potential complication. Furthermore, symptoms like frequent bloating and abdominal discomfort can significantly disrupt daily activities and diminish the quality of life for individuals affected by cow's milk allergy. 

Prevention

The most effective strategy for preventing a milk allergy reaction is to diligently avoid milk and its derivatives in food and beverages. This involves carefully checking food labels for any milk ingredients. If uncertain about a particular item, it's advisable to refrain from consuming it until its ingredients can be confirmed. Individuals with a cow's milk allergy should also avoid other dairy sources, including condensed milk, powdered milk, evaporated milk, and milk from other animals, such as goats and sheep. It's essential to avoid products such as butter, cream, cheese, custard, pudding, yogurt, sour cream, and similar items to reduce the risk of allergic reactions.

When to see a doctor?

If you experience cow's milk allergy symptoms, promptly discuss them with your doctor. Your doctor will refer you to an allergy specialist for further evaluation and treatment if necessary. It's important to undergo regular check-ups if you have milk allergy symptoms. Contact your doctor or the emergency department immediately if you exhibit signs of anaphylaxis.

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