Cow's Milk Allergy

Cause. Cow’s milk allergy is a complex disorder involving an abnormal immunological response to one or more of milk’s proteins and more than one immunological mechanism (8). Most major cow’s milk proteins, both casein and whey (e.g., β-lactoglobulin,
α-lactalbumin), have been implicated in allergic responses (8,13). Immunological mechanisms underlying cow’s milk allergy include IgE-mediated allergy (immediate hypersensitivity), which is the most common, and non-IgE-mediated cow’s milk allergy (delayed hypersensitivity) (8).

The reasons why some individuals develop cow’s milk allergy are not well understood, but are thought to involve a complex interaction between genetic and environmental factors (8,14). A family history of atopy and early exposure to cow’s milk are risk factors for cow’s milk allergy.

Prevalence and Prognosis. Cow’s milk protein allergy develops in approximately 2% of infants and young children (7,8,10,15-17) and is even rarer in adults (0.1% - 0.5%) (8). The prevalence of cow’s milk allergy in children is often overestimated, particularly by parents (18), and in the general population if the condition is self-diagnosed (12). The overall prognosis of cow’s milk allergy is good, with 80% to 90% of affected infants naturally developing tolerance to cow’s milk by 5 years of age (8,17,19).

Clinical Symptoms and Diagnosis. Symptoms related to cow’s milk protein allergy include one or more of cutaneous (e.g., eczema, rashes), gastrointestinal (e.g., nausea, vomiting, diarrhea), or respiratory (e.g., asthma, rhinitis, wheezing) manifestations (8,15-17). Life-threatening anaphylactic reactions to cow’s milk are extremely rare (15).

The generally accepted procedure to diagnose cow’s milk allergy involves a medical history to verify that the symptoms are related to milk intake, a physical exam to exclude other causes of adverse reactions, and laboratory tests to identify the specific offending allergen (7,10). In individuals older than one year, either a skin prick test or RAST (radioallergosorbent test) can be used to help diagnose IgE-mediated cow’s milk protein allergy (19). If the history, physical exam, and allergy testing point to milk as a potential allergen, the diagnosis is confirmed by well-defined elimination and subsequent oral challenge procedures (7,16,17). In young infants, open challenges are reliable when performed in an appropriate clinical setting. Double-blind, placebo-controlled food challenge testing remains the “gold standard” or the most conclusive method to diagnose cow’s milk protein allergy (7,15-17). The double-blind, placebo-controlled food challenge should not be used when there is a history of life-threatening anaphylaxis to a suspected food (7,19).

The prevalence of cow's milk protein allergy is relatively rare in infants and young children (~2%) and is generally outgrown by 5 years of age.

Management and Prevention. The only effective management strategy for cow’s milk protein allergy is avoidance of cow’s milk, products derived from cow’s milk (yogurt, cheese, cream), and food ingredients derived from cow’s milk that contain appreciable intact or partially hydrolyzed milk proteins (casein, caseinates, whey, whey protein concentrates, milk solids, casein hydrolysates, whey hydrolysates ) (8,10). Management of existing cow’s milk allergy should be aimed at relieving symptoms without compromising nutritional status or growth (8,19). Because restricting dairy food intake in children diagnosed with cow’s milk allergy can lead to poor nutritional outcomes for growth and bone health (20-22), elimination diets should be undertaken with the advice of a physician and/or dietitian while closely monitoring children’s growth and development (8,19,23).

Formula-fed infants with confirmed cow’s milk allergy may benefit from the use of hypoallergenic or soy formula (10,19,23-25). Nearly all infants with cow’s milk allergy tolerate extensively hydrolyzed formulas (i.e., formulas in which most of the milk protein has been broken down into free amino acids and peptides) (23,24). If allergic symptoms persist, an elemental formula based on amino acids is generally used (23). Because formulas based on partially hydrolyzed cow’s milk proteins can elicit allergic reactions, they are not recommended for infants with cow’s milk allergy (7,24).

Although soy protein allergy is less common than cow’s milk protein allergy, some infants and children who experience adverse reactions to cow’s milk protein experience similar reactions to soy protein (7,8,25). Nevertheless, the American Academy of Pediatrics indicates that most infants with documented IgE-mediated allergy to cow’s milk will tolerate soy protein-based formula (23). Diagnosis of cow’s milk allergy should be periodically reconfirmed to avoid the elimination of cow’s milk for longer than necessary.

The inclusion of milk proteins in an ever-expanding array of processed foods presents a challenge for children and adults with cow’s milk allergy (8). However, since passage of the U.S. Food Allergen Labeling and Consumer Protection Act (FALCPA) (Public Law 108-282) (26), it is now much easier to identify and avoid foods that contain cow’s milk protein. According to this law, products labeled on or after January 1, 2006 must clearly indicate the presence of any of the eight major food allergens, one of which is milk, using their “common or usual name” on product labels. If a product contains milk-derived casein, the product’s label must use the familiar term “milk” in addition to the less familiar term “casein” so that people with milk allergies clearly understand the presence of the allergen they need to avoid.

Efforts aimed at preventing cow’s milk allergy should focus on high risk infants (i.e., those born to parents with a history of allergies). Even among these infants, the development of cow’s milk allergy is relatively uncommon. Simple dietary strategies may help prevent cow’s milk allergy in high risk infants (14,19). The American Academy of Pediatrics advises breastfeeding or a hypoallergenic formula, or possibly a partial hydrolysate formula as preventive measures, but acknowledges that “conclusive studies are not yet available to permit definitive recommendations” (19). Although rare, sensitization to cow’s milk protein can occur prenatally and in breast-fed infants (8). Further study is needed to determine if maternal dietary exclusion during pregnancy and/or lactation minimizes risk of cow’s milk allergy in infants, and if any reduction in risk is out-weighed by adverse effects on maternal nutrition (8,27). Soy formula is not recommended to prevent food allergy in high risk infants (19,28,29). Intake of probiotics, especially lactic acid bacteria, during pregnancy, lactation, and in infant formulas may reduce food allergies, including milk protein allergy, in at-risk infants (30-32).