Food allergy or hypersensitivity refers to an abnormal immunologic reaction in which the body's immune system produces an allergic antibody, called immunoglobulin E (IgE) antibody, to usually harmless foods, such as milk or egg protein, resulting in allergy symptoms such as wheezing, diarrhea or vomiting.
Food allergy is different from food intolerance. The term "food allergy" is sometimes used in a vague, all-encompassing way, muddying the waters for people who want to understand what a real food allergy is.
True food allergies are serious and, in rare cases, can be fatal. Intolerance to milk and other foods is much more common and usually less serious than allergy. Food intolerances may produce symptoms similar to food allergies, such as abdominal cramping. But while people with true food allergies must avoid certain offending foods altogether, people with food intolerance can often eat small amounts of the offending food without experiencing symptoms.
Lactose intolerance is sometimes mistaken for milk allergy. Lactose intolerance is a condition in which a person lacks the enzyme to break down the sugar found in milk for proper digestion. This results in bloating, abdominal discomfort and diarrhea.
Estimates are that up to 80 percent of African-Americans have lactose intolerance, as do many people of Mediterranean or Hispanic origin. It is quite different from the true allergic reaction that some people may have to the proteins in milk.
Food allergens, those parts of foods that cause allergic reactions, are usually proteins. Most of these allergens can still cause reactions even after they are cooked or have been digested in the intestines. Numerous food proteins have been studied to establish allergen content.
Recent studies indicate that the protein in cow's milk is one of the most common food allergens. The protein of cow's milk is composed of two types: casein (80 percent) and whey (20 percent). Since most of these allergens are heat resistant, scalding or boiling the milk will not help in most cases. People who must avoid milk because of allergies should be sure to get adequate calcium and vitamin D in their diets.
Egg allergy can be quite dangerous in children. It is the white, not the yolk, that causes the problem, and raw white is more likely than cooked to provoke symptoms. But even cooked whites may be potent allergens, and an egg-sensitive person should avoid the yolks, since they will often be contaminated with whites.
Milk allergy can be manifested as asthma, eczema (an itchy rash), rhinitis (inflamed nose), and gastrointestinal distress, as well as bleeding, pneumonia, and even anaphylaxis (shock). Every parent should be alert for signs of milk allergy.
Keeping a food diary may be helpful. The most common way to test for food allergies is with an "elimination diet," in which all common allergy-causing foods are eliminated over a few weeks until symptoms lessen. The foods are then re-introduced to see which cause the symptoms to return. An elimination diet should not be undertaken without very specific guidance and supervision from a doctor.
Allergy testing for foods done either as a blood test (called a RAST test) or by skin testing is helpful if multiple foods are suspected, if there is no clear indication that food is causing the symptoms, if symptoms are serious such as when difficulty breathing has occurred and to determine if the food allergy has been outgrown.
The basic principles of treating food allergy are (1) avoidance of the allergen, and (2) symptomatic therapy.
Avoidance of specific foods is critical once a true food allergy has been diagnosed by your physician. Soy-based formulas are available for infants with milk allergy. Patients allergic to milk must be extra vigilant because processed food may contain milk products labeled as "natural flavorings" or "seasonings."
Frequently, an emergency medication called epinephrine (available as EpiPen or Twinject) is recommended. Parents and children must be trained in how and when to administer these medications, and if prescribed, they should carry them at all times.
If the epinephrine is given, it is absolutely essential that the child be brought to a hospital, preferably by ambulance, and observed for 4-6 hours since the reaction may reoccur even without any further food ingestion.
Parents should consider a consultation with an allergist if the diagnosis is in doubt or if a serious reaction to a food has occurred.
Many children with a milk or egg allergy will outgrow the allergy by the time the child is 3 to 5 years old. If the child has experienced a serious reaction to the food in the past, parents should never try giving the child the food unless recommended by their physician. It may be smart to administer the food for the first time in the physician's office or clinic where emergency treatment is available should a significant reaction occur.