|Classification and external resources|
A milk allergy is a food allergy, an adverse immune reaction to one or more of the constituents of milk from any animal (most commonly alpha S1-casein, a protein in cow's milk). This milk-induced allergic reaction can involve anaphylaxis, a potentially life-threatening condition.
It is distinct from lactose intolerance, which is a nonallergic food sensitivity, and comes from a lack of production of the enzyme lactase, required to digest the predominant sugar in milk. Lactose intolerance is considered the normal state for most adults on a worldwide scale and is not typically considered to be a disease condition.
Signs and symptoms
The effects of antibody-mediated allergy are rapid in onset, evolving within minutes or seconds. These allergies always arise within an hour of drinking milk; but can occasionally be delayed longer when eating food containing milk as an ingredient. The effects of non-antibody-mediated allergy is delayed; because it is not caused by antibodies, it can take several hours, or even up to 72 hours to produce a clinical effect. The most common symptoms for both types are hives and swelling, vomiting, and wheezing, with symptoms first arising in skin, then the GI tract, and less commonly, the respiratory tract. Milk allergy can cause anaphylaxis, a severe, life-threatening allergic reaction, but this is rare.
The major allergens in cow milk are αs1-, αs2-, β-, and κ-casein and the whey proteins α- and β-lactoglobulin. The body may raise an antibody-based immuneresponse or a cell-based immune response to these allergens.
Diagnosis is carried out by first doing a diagnostic elimination diet, skin prick tests, measuring IgE in blood, and conducting in-office food challenges. A double-blind, placebo-controlled food challenge is still the gold standard for the diagnosis for all food allergies, including milk allergies. A negative IgE test doesn't rule out cell-based allergy, and the double-blind, placebo-controlled food challenge is important to rule out this form of allergy.
Because proteins in various mammalians are often cross-reactive, other forms of milk should not be substituted.
Milk substitute formulas are used to provide a complete source of nutrition for infants. Milk substitutes include soy-based formulas, hypoallergenic formulas based on partially or extensively hydrolyzed protein, and free amino acid-based formulas. Nondairy-derived, amino acid-based formulas, known as amino acid formulas or elemental formulas, are considered the gold standard in the treatment of cows'-milk allergy when the mother is unable to breastfeed. Milk substitutes from soy, nuts and the like should not be considered as they are not nutritionally equivalent.
The elimination diet should be tested every six months by testing milk-containing products low on the "milk ladder", like fully cooked foods containing milk, in which the milk proteins have been denatured, and ending with fresh cheese and milk.
Treatment for accidental ingestion of milk products by allergic individuals varies depending on the sensitivity of the person. Frequently medications such as an epinephrine pen or an antihistamine such as diphenhydramine (Benadryl) are prescribed by an allergist in case of accidental ingestion. Sometimes prednisone will be prescribed to prevent a possible late phase Type I hypersensitivity reaction.
Generally, affected infants lose clinical reactivity to milk during early childhood or at latest by adolescence; around half the cases resolve within the first year and 80-90% resolve within five years.
Between 13% and 20% of children allergic to milk are also allergic to beef.
Milk allergy is the most common food allergy in early childhood. It affects between 2% and 3% of infants in developed countries; the incidence in only-breastfed infants is lower, at about 0.5%. These figures appear to be antibody-based allergy; allergy based on cellular immunity is uncertain.
Desensitization, which is a slow process of eating tiny amounts of milk, until the body is able to tolerate more significant exposure, results in reduced symptoms or even remission of the allergy in some people and is being explored for milk allergy. This is called oral immunotherapy. Sublingual immunotherapy may be somewhat safer, but less effective. A 2014 meta-analysis found desensitization to be relatively safe and effective but found that further study was needed to understand the overall immune response to it, and questions remain open about duration of the densensitization.
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