Allergic eczema, also known as atopic dermatitis, is a chronic itchy skin rash. Atopic dermatitis most often begins in infancy or early childhood and resolves or improves in most cases by age 10 years. In a minority of cases, it can continue into adulthood or may first appear later in life. This rash primarily involves skin on the creases of the arms (where the forearm and upper arm connect), behind the knees, and to a lesser extent on the ankles, wrists, face, neck, and upper chest. In adults, atopic dermatitis can also affect the skin around the eyes, including the eyelids.
The causes of atopic dermatitis are not completely understood, but we do know that persistent allergic inflammation is present in the skin, which contributes to or coexists with a significant defect in the skin’s ability to hold on to moisture. Patients with atopic dermatitis are universally sensitive to a number of nonspecific environmental factors, including hot baths or showers, low environmental humidity, soaps and detergents, and prickly fabrics, such as wool.
Along with the above factors, food allergy has a particularly important role in triggering outbreaks of the rash in children, and it has been estimated that up to 25% of children will have an allergic reaction to at least one food. The most common reaction to allergenic foods in patients with atopic dermatitis is redness and itching of the skin, anywhere on the body, and usually occurring within 30 to 60 minutes after eating. The foods that have been implicated in triggering atopic dermatitis most frequently are milk, eggs, wheat, soy, peanuts, and tree nuts. Allergy to these foods is diagnosed , by prick/puncture skin testing or blood tests for food IgE.
If a number of foods are identified by testing, and it is unclear which are actually triggering the rash, your allergist may recommend oral food challenges. In a food challenge, the food of interest is given to the patient, starting with a very small quantity and gradually increasing the dose. The development of a rash or other symptoms, such as diarrhea, indicates that the patient is allergic to that food. In some cases, avoiding allergenic foods may have a profound effect upon the daily occurrence of rash and itching.Airborne allergens, such as house dust mites, animal danders, molds, and pollens, have also been shown to aggravate atopic dermatitis.
The results are less consistent than those seen with foods. However, in patients with hypersensitivity to avoidable allergens, such as mites, animals, and molds, allergen avoidance measures should be instituted as rigorously as possible in hopes of reducing the need for medications. Atopic dermatitis frequently runs in families in which other family members have asthma or hay fever. About three out of five infants or children who have atopic dermatitis later develop hay fever and asthma.