Chapter 4. Avoidance of Allergens
Some atopic dermatitis patients may have, or develop allergies to specific foods or aeroallergens, that may be concurrent with atopic dermatitis, and in a subset, may serve as disease triggers. In patients with more severe dermatitis, difficult to control disease, or a history suggestive of allergies, evaluation is appropriate.
Food allergens have been shown to play a role in a subset of patients with atopic dermatitis. In children who have undergone controlled food challenges, milk, egg, peanut, wheat, soy, and fish account for approximately 90% of food allergens that can exacerbate atopic dermatitis. Controlled food challenges were first instituted at the authors’ center in the 1970’s, recognizing that a positive allergy skin test or RAST to a food allergen did not necessarily define clinical relevance. In fact, most patients with food-associated atopic dermatitis will be infants or young children and most will have clinically relevant food allergies to only one, two or three foods (rarely more) irrespective of the number of positive skin tests or RAST. Thus, extensive elimination diets are rarely indicated.
Food challenges are usually done after first clearing up the patient’s eczema or at least after establishing a stable baseline and the specifics of such procedures have been published (e.g. Bock SA, et al. Double-blind, placebo-controlled food challenge (DBPCFC) as an office procedure: a manual. J Allergy Clin Immunol 1988;82:986-97). If the patient has asthma or a history of anaphylaxis, then such challenges should be performed in a center with experience in dealing with such patients.
Once clinical correlation is demonstrated, removal of a proven food allergen from a patient's diet can lead to significant clinical improvement. Of note, it is important for patients to completely avoid implicated foods, as even small amounts of the allergen can contribute to synthesis of food-specific IgE.
Organizations such as the Food Allergy and Anaphylaxis Network can provide valuable information on hidden sources of common food allergens, recognizing specific food proteins by various names on food labels and methods of preparing certain foods with safe substitution of allergenic ingredients.
It is important to educate caregivers that most children will become tolerant to certain food allergens such as milk, egg or soy protein, even in the face of positive skin tests. Thus, following the natural history of food-related atopic dermatitis is important. While food challenges have been utilized to help define the natural history of food allergy, more recently, quantitation of specific IgE levels for four food allergens measured by the Pharmacia CAP System FEIA (egg ³7 kUA/L, milk ³15 kUA/L, peanut ³14 kUA/L and fish ³20 kUA/L) have been shown to be associated with a > 95% chance of clinical reaction. It is important to recognize that levels of specific IgE below these defined threshold values can be associated with significant allergic reactions. In clinical practice, a child with a history of milk protein exacerbated atopic dermatitis whose milk-specific IgE is ³15 kUA/L would not need to undergo an oral milk challenge. By following the food-specific IgE level over decisions can be made to help determine when a food could be re-introduced.
The issue of prevention of atopic dermatitis with dietary manipulation is often raised by expectant parents. In one prospective study, restricting the mother's diet during the third trimester of pregnancy and lactation and the child's diet during the first 2 years of life resulted in decreased prevalence of atopic dermatitis in the prophylaxis group compared with a control group at 12 months of age but not at 24 months. Follow-up through 7 years of age showed no difference between the prophylaxis and control groups for atopic dermatitis or respiratory allergy. In another study, breast feeding did not affect the lifetime prevalence of atopic dermatitis in a large ethnically and socially diverse group of children. In contrast, however, one 17 year prospective cohort study found that infants who were breast fed exclusively for more than 6 months had a significantly lower prevalence of eczema at 1 year (all infants) and 3 years (infants with a family history of atopy) compared to infants who were breast fed for less than 1 month or intermittently breast fed.
While the benefits of breast feeding infants with atopic dermatitis have been touted, sensitization to allergens in the mother’s diet transferred through breast milk is a potential problem for at risk infants. In one group of exclusively breast fed infants with atopic dermatitis, cessation of breast feeding and institution of an amino acid formula compared to continued breast feeding, even with maternal elimination diet resulted in improvement in a number of clinical parameters including extent and intensity of eczema. In addition, nutritional and growth parameters also improved when breast feeding was discontinued in this population.
The degree of sensitization to aeroallergens has also been shown to be associated with the severity of atopic dermatitis in some patients (see chapter 3). Importantly, environmental control measures aimed at reducing dust mite allergen load including the use of dust mite-impermeable covers for pillows and mattresses have been shown to improve atopic dermatitis in patients allergic to dust mite allergen. Although some studies have not found such benefit, this may reflect the population studied (adults vs children), the need to reduce allergen exposure in environments other than the bedroom or that additional factors could be contributing to chronic skin inflammation. Of interest, in one study even patients not sensitized to dust mite allergen benefited from use of mite-proof covers, suggesting that such covers may reduce exposure to other allergens, irritants or possibly superantigens. Dust mite-impermeable covers for pillows and mattresses appear to be a simple and relatively low cost environmental control measure and can be obtained from a number of sources, for example:
It is worth having caregivers purchase slightly more expensive cotton treated fabrics, which are more durable and comfortable than vinyl covers. In addition, covers should be placed on all the beds in the room that a dust mite allergic patient sleeps in. In fact, patients have been referred for poorly controlled atopic dermatitis with encasings on their pillow and mattress, but sleeping in the bottom bunk of a bed with no covers on the upper mattress!
In addition, it is worth remembering that young patients often spend more time in parents’ beds than their own. While no controlled studies have looked at avoidance of furred animals in homes of patients with atopic dermatitis, for patients sensitized to animal allergens, avoidance of such allergens indoors makes sense based on our current understanding of allergic inflammation.