EczemaNet Spotlight Article
Not Every Child with Atopic Dermatitis Needs Allergy Testing

The role that allergy testing plays in managing atopic dermatitis is often confusing. Allergies can trigger atopic dermatitis, so parents frequently ask if their child should have allergy tests. Concerned parents often believe that if only the allergies could be identified, the child could avoid the allergens. This, in turn, would bring much-needed relief.

The truth is no one thing — not even allergen avoidance — can control atopic dermatitis. Successfully managing this complex condition requires a multi-faceted approach. Proper skin care, using medication as directed, and avoiding common skin irritants such as wool clothing all play a role. For most patients, sticking to this plan keeps atopic dermatitis under control.

Who May Benefit from Allergy Testing
For patients with severe atopic dermatitis and those whose condition seems resistant to treatment, allergy testing can be beneficial. An estimated one-third of patients with atopic dermatitis have food allergies. For a few of these patients, eating foods to which they are allergic causes eczema to flare. Why this happens is not entirely clear, but research shows that it most commonly occurs in infants and patients with severe disease.

Types of Allergy Tests
To identify allergens, a doctor takes a complete medical history and orders appropriate allergy tests. When the doctor suspects an allergy caused by food or something in the environment, one of the following tests may be ordered. An allergist generally performs these tests:

  • Blood test – When an allergic reaction occurs, specific antibodies appear in the blood. This test, called a RAST test, measures antibodies associated with allergic reactions.

  • Skin prick test – Also called the scratch test, this is the most common allergy test. It involves placing a small amount of suspected allergens on the patient’s skin, often on the forearm or back. The skin is then scratched or pricked so that the each substance can get beneath the skin. Allergic reactions develop within 15 to 20 minutes. If a reaction occurs, the skin tends to itch and the area may swell or turn red.

Another type of allergy test is used to detect cutaneous allergens (substances that cause an allergic reaction on the skin). Called a patch test, it is usually performed by a dermatologist. As the name implies, this test requires the patient to wear a type of patch on the skin. Each patch, also called a panel, contains a number of common allergens. The patient usually wears the panel(s) for 48 hours, returning once before the 48-hour period for an initial reading. The second reading is usually taken at 48 hours. During each visit, the dermatologist evaluates the reactions on the skin.

Test Results Can Be Misleading
Results that indicate food allergies can be especially misleading. While a negative result provides strong evidence that the child is not allergic to a food, false positive results are common. Dermatologists also find that while the test can indicate a food allergy, eating the suspect food usually does not cause the child’s eczema to flare.

The only reliable way to find out if a food actually causes the eczema to flare is to perform a food challenge test. This requires the child to eat the suspect food while being observed by a medical professional. If the child develops signs of eczema — redness, papules, and wheals — or has increased and widespread itch within 2 hours of eating the food, the test concludes that the food causes eczema to flare.

Study after study finds that this reaction is exceeding rare. Even children hospitalized for severe and recalcitrant atopic dermatitis seldom test positive when given a food challenge test. A study conducted in Oregon found only 1 positive food challenge in 17 children hospitalized due to severe atopic dermatitis that had not responded to treatment.

In all, 58 food challenges were performed. The foods tested were those most commonly associated with food allergies — eggs, milk, wheat, and soy. Nuts were not tested because life-threatening allergic reactions can occur. The study concluded that while food allergies are common in patients with atopic dermatitis, eating foods to which they are allergic rarely causes atopic dermatitis to flare. This finding has been observed in similar studies.

Another study suggests that even in children who have food allergies, relief comes from caring for the child’s skin. This study found that when children with moderate to severe atopic dermatitis received long-term — at least 3 months — treatment with tacrolimus ointment, the severity of the eczema decreased significantly. With the eczema under control, the number of parents who reported that the eczema worsened after the child ate certain foods also decreased. Parents concerns about food allergy also declined dramatically. The researchers attributed these changes to better control of the atopic dermatitis.

Skin Care Plays Central Role
Most dermatologists advise parents to focus on caring for the child’s skin. Follow your dermatologist’s skin care guidelines, use medication as directed, and help the child avoid common triggers such as becoming overheated. If these fail to control the child’s atopic dermatitis, then it is time to ask about allergy testing.

For more information about skin care for atopic dermatitis, read Daily Skin Care Essential to Control Atopic Dermatitis.

References:
1 Halbert AR, Weston WL, Morelli JG. Atopic dermatitis: is it an allergic disease? Journal of the American Academy of Dermatology 1995; 33: 1008-18.

2 Kerschenlohr K, Darsow U, Burgdorf WH et al. Lessons from atopy patch testing in atopic dermatitis. Current Allergy and Asthma Reports 2004; 4: 285-9.

3 Rowlands D, Tofte SJ, Hanifin JM. Does food allergy cause atopic dermatitis? Food challenge testing to dissociate eczematous from immediate reactions. Dermatologic Therapy 2006; 19: 97-103.

4 Thompson MM, Hanifin JM. Effective therapy of childhood atopic dermatitis allays food allergy concerns. Journal of the American Academy of Dermatology 2005; 53: S214-9.

5 Tofte SJ, Hanifin JM. Current management and therapy of atopic dermatitis. Journal of the American Academy of Dermatology 2001; 44: S13-6.


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Page last updated 10/15/07

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