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
– 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
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