Symptoms of Milk Allergy & Food Allergy in Children

Cow’s milk is the most frequently encountered food allergen in infancy, and milk allergy is often the earliest indicator that a baby is atopic. Precise figures of the incidence of cow’s milk allergy (CMA) are hard to find because of the difficulties in obtaining an accurate diagnosis, differences in the populations used for research studies, and disagreement about the symptoms (clinical criteria) for the condition.

All studies agree, however, that cow’s milk allergy is most prevalent in early childhood with an incidence of 2 to 7.5 percent being reported. About 80 to 90 percent of children outgrow early cow’s milk protein allergy by the age of 5 years, and the incidence of cow’s milk allergy in adults is reported to be only about 0.1 to 0.5 percent of the population.

Milk is an extremely complex food with multiple proteins. Many of its proteins have the capacity to act as allergens and to elicit immunological responses in sensitized individuals. To increase the complexity of cow’s milk protein allergy, different individuals react to different proteins. There can be considerable differences in the immunological response to each different protein, resulting in several quite distinct clinical presentations of cow’s milk allergy. These factors often lead to problems for doctors in diagnosing the condition in babies and food allergy in children.

Several practitioners have attempted to classify cow’s milk protein allergy, on the basis of immunological work mechanism and clinical presentation, to aid in diagnosis.

A 1995 report identified three distinct types of infant CMA with different symptoms and laboratory findings.

Group 1
• Symptoms developed within minutes of ingestion of small volumes of cow’s milk.
• Symptoms included hives, tissue swelling (angioedema), eczema, and gastrointestinal and respiratory allergy symptoms that were part of a generalized anaphylactic reaction varying in severity from child to child.
• Skin prick tests to milk allergen were positive.

Group 2
• Symptoms were confined to the digestive tract.
• Vomiting and/or diarrhea developed several hours after ingestion of modest volumes of cow’s milk.
• Skin prick tests to milk allergen were mostly negative.
• This group was described as suffering from cow’ smilk protein enteropathy.

Group 3
• Symptoms developed in the gastrointestinal tract more than 20 hours after ingesting large volumes of milk.
• Sometimes symptoms in the gastrointestinal tract were accompanied by respiratory symptoms and eczema.
• Skin prick tests to milk allergen were less marked than for the patients in Group 1 and usually occurred only in those children with eczema or food allergy in children.

This report highlights some important factors in cow’s milk allergy diagnosis:
• Symptoms can develop from minutes after ingestion of cow’s milk to up to 20 hours later.
• Skin prick tests are of very limited value in diagnosing the condition.
• The prevalence of gastrointestinal symptoms makes the distinction between cow’s milk protein allergy and lactose intolerance difficult to determine on clinical signs alone.

Symptoms of Milk Allergy

Most often, symptoms of milk allergy appear in the skin—where eczema, hives, and swelling (angioedema) may occur—and in the gastrointestinal tract, with abdominal bloating, pain, gas, diarrhea, constipation, nausea, vomiting, and, occasionally, blood in the stool (occult blood). In some individuals, upper respiratory tract symptoms and asthma may be caused or worsened when milk or dairy products are consumed.

Blood in the stool, often difficult to see because it is hidden within the feces (called occult blood loss), associated with cow’s milk allergy can be a cause of iron-deficiency anemia. This is especially the case in children, because blood is the most important source of iron in the body.

Another effect of cow’s milk allergy that is currently being investigated in children is the inability to fall asleep and trouble with restless, disturbed sleep. In an infant, inadequate growth and weight gain (failure to thrive) may be a result of cow’s milk protein allergy. The allergic reaction results in inflammation in the intestines, and absorption of nutrients may be impaired as a result of damage to the transport mechanisms that reside in the intestinal cells.

Although very rare, cow’s milk allergy can be a cause of fatal anaphylaxis in very young children. In 2000, a study from the United Kingdom3 reported 8 fatal cases of anaphylaxis from food allergy in children under the age of 16 in the 10 years from 1990 to 2000. Four children died from cow’s milk protein allergy, and one from the inappropriate use of injection adrenalin to treat a mild reaction to a food. None died from eating peanuts allergy. This report emphasizes the fact that cow’s milk allergy in early childhood cannot be taken lightly but should always be treated with the utmost care and caution.

The diagnosis of cow’s milk protein allergy is not a simple matter. Any adverse reaction experienced after drinking milk is often ascribed to cow’s milk allergy. However, when the symptoms of milk allergy are localized in the gastrointestinal tract, the problem may be lactose intolerance, not an immunologically mediated allergy to milk proteins. It is important to differentiate between lactose intolerance (lactase deficiency) and cow’s milk protein allergy because some symptoms, such as abdominal pain, diarrhea, and vomiting, may be common to both conditions. However, cow’s milk allergy can cause inflammation of the gastrointestinal tract and then trigger a lactase deficiency, so it is possible for both conditions to exist together. Symptoms of milk allergy in other organ systems, such as the respiratory tract and the skin, are never symptoms of lactose intolerance. If these occur as a result of drinking milk, it is clear that cow’s milk allergy is also a problem.