How Are Allergies and Atopic Dermatitis Related?

An allergen is a substance that causes an allergic reaction in the body. Allergens are commonly triggers for atopic dermatitis (eczema), although the allergens that cause a reaction may differ between individuals, and not everyone with atopic dermatitis finds that allergens are a trigger. Common allergens that trigger atopic dermatitis include certain foods, pet dander, dust mites, molds, and pollens.1

How eczema causes sensitivity to allergens

Researchers believe that the dysfunction in skin barrier seen in atopic dermatitis leads to an increased sensitivity to allergens. In healthy skin, the barrier provides adequate protection against germs and environmental allergens, but in people with atopic dermatitis, the barrier is compromised, providing an opening for these germs and allergens to enter the body. The immune system in atopic dermatitis is also dysfunctional, creating more of an inflammatory and allergic response.2

Food allergies

A significant number people with atopic dermatitis have food allergies. Food allergies are more common in children with atopic dermatitis, with an estimated 20-40% of children with atopic dermatitis having food allergies that worsen their disease. A smaller number of adults with atopic dermatitis have food allergies. The most common food allergies that worsen atopic dermatitis include cow’s milk, eggs, fish, peanuts, soy, tree nuts, and wheat. Children with food allergies often outgrow their sensitivity, developing a tolerance over time, and the American Academy of Dermatology recommends retesting as the child ages. Even if a person with atopic dermatitis tests positive for food allergies, it does not necessarily mean that all their food allergies are relevant to their atopic dermatitis. Food allergies are true triggers of atopic dermatitis in only a small subset of patients, and experts do not generally recommend food elimination diets solely on the basis of positive food allergy testing.1,3

Environmental allergies

Allergens in the air that are common triggers for atopic dermatitis include molds, pollens, pet dander, dust mites, and fungi. The presence of allergies to airborne allergens increases with age, and higher rates of sensitivity to allergens are noted in people with moderate to severe atopic dermatitis. With some airborne allergies, like pollen or mold, there are seasonal increases in symptoms. Other people notice a flare in their atopic dermatitis when they come into contact with an allergen, such as pet dander.3

Contact allergies

Some people with atopic dermatitis also have allergic contact dermatitis, where the skin develops an allergy to a substance that comes into contact with it. Common causes of allergic contact dermatitis include cosmetics, adhesives, or metals (like nickel). In those people who have both atopic dermatitis and allergic contact dermatitis, avoiding relevant allergens is important as they can exacerbate both conditions.4,5

Testing for allergies

People with atopic dermatitis have a higher rate of environmental and food allergies, and doctors assess for these conditions during a patient history. Those patients that have symptoms of allergies or whose atopic dermatitis is persistent or difficult to treat may receive additional testing for allergens. Tests for allergens include skin prick testing and blood tests.3

Skin prick testing

Skin prick testing involves applying a diluted allergen with a prick or puncture on the surface of the skin. The skin is observed for approximately 15 minutes to see if a reaction develops. A positive reaction to the allergen is a “wheal,” a raised, red bump and a surrounding “flare,” of area of redness.6

Blood tests

Blood tests involve testing for allergen specific IgE (Immunoglobulin E, antibodies produced by the immune system that begin the process of an allergic reaction). Negative test results can be helpful to rule out specific allergies, like foods, but positive test results only identify sensitization and require additional information to confirm.3

Patch tests

Patch tests use patches containing allergens that are placed on the skin and worn for 48 hours. Patch tests can be helpful to detect contact dermatitis, an allergic skin irritation, as well as detecting delayed allergic reactions.7

Food elimination diets

Another alternative for testing for food allergies is food elimination diets, however, excessively restrictive diets can lead to weight loss, poor growth, calcium deficiency, and other complications in children. People considering food elimination diets should talk with their doctor.3

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Emily Downward | June 2017