Atopic dermatitis, one of the most common forms of eczema in this family of inflammatory skin diseases, is a chronic disease marked by red, cracked and itchy skin. Now, increasing evidence indicates atopic dermatitis is a precursor to allergic diseases rather than a consequence. Dermatologists are advising parents of infants and young children affected by this common skin condition to be aware of the potential for future food allergies.
Speaking February 4 at the 69th Annual Meeting of the American Academy of Dermatology (Academy), dermatologist Jon M. Hanifin, MD, FAAD, professor of dermatology at Oregon Health & Science University in Portland, discussed the link between atopic dermatitis and food allergies, as well as the new food allergy guidelines issued in December 2010 by the National Institute of Allergy and Infectious Diseases (NIAID).
"Considering that six to 10 percent of children have atopic dermatitis and that up to one-third of those individuals may have documented food allergy, the number of these children affected by food allergies may be significant," said Dr. Hanifin. "In most cases, patients experience atopic dermatitis before food allergies, so it is important for parents of infants and small children affected by this skin condition to be aware of the risk of food allergies."
A recent five-year multi-center study conducted by Dr. Hanifin and others in babies age three to 18 months found that even in reported mild cases of atopic dermatitis, roughly 15 percent of infants had definite food allergies. Dr. Hanifin further explained that patients with more severe cases of atopic dermatitis generally have a higher incidence of developing food allergies. Although this study and others confirm the strong correlation between atopic dermatitis and food allergies, proper testing for a food allergy -- as recommended in the new guidelines -- is critical in determining if an actual food allergy exists.
The new NIAID food allergy guidelines clearly define a food allergy as an adverse health event that stems from an immunologic reaction upon exposure to a specific food. Typically, a food allergy occurs rapidly (within 30 minutes from the time a person is exposed to the food), with skin symptoms such as hives and itching of the lips. More severe reactions may include respiratory, gastro-intestinal or anaphylaxis problems that could be potentially very dangerous.
In contrast, sensitization to food is not the same as being allergic to food. Specifically, an allergic sensitization to food is determined by the presence of specific IgE antibodies -- which are antibodies made in response to foreign proteins that come into contact with the body -- in the blood and confirmed by blood or skin tests.
In order to understand the complex relationship between food allergies and atopic dermatitis, Dr. Hanifin noted that people with atopic dermatitis make larger amounts of IgE than any other group of patients.
"As dermatologists, we have seen children with highly restrictive diets who might have more than 20 positive skin or blood tests -- but we now know that a positive test is not an allergy unless it is confirmed by an actual food challenge," said Dr. Hanifin. "In the meantime, children may be malnourished and experience a host of other problems by not having proper nutrients in their diets. The fact is that children may only have a sensitization to the foods, but are being treated as if they have food allergies. We're hoping that these new guidelines will help clear up this misinformation and ensure a proper diagnosis."
According to the new guidelines, it is recommended that "…children less than 5 years old with moderate to severe atopic dermatitis be considered for food allergy evaluation for milk, egg, peanut, wheat and soy, if at least one of the following conditions are met:
Dr. Hanifin further explained that in the past, positive blood tests and skin tests would be mistaken for a food allergy, because they would indicate the presence of IgE antibodies -- which are higher in patients with atopic dermatitis. "However, those antibodies are not diagnostic and the only way to diagnose food allergy is with a strong history of reactions or a challenge -- where you feed patients the food indicated by tests and see if they have an immediate reaction to it," said Dr. Hanifin. "This is done in a doctor's office, using small increments of the food in question and increasing the amount until an allergic reaction occurs or does not occur. Usually a parent can pinpoint if a child has a true food allergy because the allergic reaction will appear so quickly with lip swelling or hives, quite distinct from simply food intolerance."
Recent research examining the genetic basis of atopic dermatitis has shown that this chronic skin condition is likely related to a defect in the skin's protective outer layer -- known as the epidermal barrier -- allowing irritants, microbes and allergens (such as food) to penetrate the skin and cause adverse reactions. Since the skin barrier in patients with atopic dermatitis is compromised and open to absorb proteins, it allows sensitization to certain foods, leading to a positive skin or blood test.
While the new guidelines establish protocol for the proper evaluation and management of food allergy, Dr. Hanifin explained that another exciting area of research is examining whether withholding foods is leading to more allergies than an unrestricted diet in young children. This may provide future insight in potential ways to prevent food allergies.
For example, Dr. Hanifin explained that studies have shown that children in Israel seldom get peanut allergy, which possibly can be attributed to the use of peanut proteins in pacifiers in that country. In the U.S. and Europe, where peanut allergies are more common, infants are not usually exposed to this food until they are toddlers -- the time when most peanut allergies are noticed.
"There is some thinking that withholding foods might actually be causing more allergies, and that an unrestricted diet may help tolerize babies to foods that could potentially cause a problem later in life," said Dr. Hanifin. "Ongoing studies in this country using oral immunotherapy -- in which you feed small amounts of food to kids to correct potential food allergies -- appear promising, and dermatologists hope that we may discover how to prevent food allergies in the future while continuing to provide successful treatment for children with atopic dermatitis."
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