Atopic Dermatitis and Allergic Contact Dermatitis Overlap in Children. Why Patch Testing to Tell Them Apart Is Important

Atopic dermatitis and allergic contact dermatitis are inflammatory skin conditions that present with similar symptoms, including red, itchy patches or plaques on the skin. The similarity in symptoms can make it difficult to tell them apart. Moreover, allergic contact dermatitis may go undiagnosed in many children who also have atopic dermatitis, according to a study published last month in the Journal of the American Academy of Dermatology,

Although these conditions have similar symptoms, they differ in pathophysiology. While atopic dermatitis is a type 2 inflammation mediated by Th2 (type 2 helper T) cells, allergic contact dermatitis is a type 4 delayed hypersensitivity reaction mediated by Th1 (type 1 helper T) cells. Both conditions are typically diagnosed during childhood, with about 16.5% of children having allergic contact dermatitis and 20% living with atopic dermatitis.

Patch testing is the current gold standard for diagnosing allergic contact dermatitis. However, less than 10% of patch tests are administered to children. Due to the similarity of symptoms between the two conditions, children already diagnosed with atopic dermatitis may not receive patch testing for allergic contact dermatitis, resulting in underdiagnosis of the comorbidity.

Hadley Johnson, a University of Minnesota medical student, led a retrospective case-control study aimed at identifying the prevalence of allergic contact dermatitis among children with atopic dermatitis.

Lead author Hadley Johnson, a student at the University of Minnesota Medical School, and colleagues conducted a retrospective case-control study to determine the prevalence of allergic contact dermatitis in children with atopic dermatitis versus those without atopic dermatitis. They also sought to evaluate which allergens more commonly elicit positive patch tests in children with atopic dermatitis.

The researchers identified 912 children referred for patch testing from 14 centers in the United States between January 1, 2018, and December 31, 2022. Of those children, 615 had atopic dermatitis, and 297 did not. Children with atopic dermatitis were more likely to have concurrent inflammatory conditions, such as asthma and allergic rhinitis compared with those without atopic dermatitis.

The study results showed that children with atopic dermatitis were more likely to have more than one positive patch test result and had more positive results overall than participants without atopic dermatitis. Nickel, commonly found in costume jewelry, was the most common allergen found to trigger a reaction in both children with atopic dermatitis and those without. Methylisothiazolinone (MI) was the second most common allergen for children with atopic dermatitis, and balsam of Peru placed second for participants without atopic dermatitis. Methylisothiazolinone is a preservative commonly found in toiletries, such as shampoo, conditioner, and soaps, as well as in other products, such as school glue and paint. Balsam of Peru is a fragrance frequently found in personal care products such as shampoo, essential oils, and perfumes.

Other allergens reported in the study include antibiotics, such as bacitracin and neomycin, and lanolin alcohol, an ingredient found in Aquaphor Healing Ointment and Eucerin Original Healing Cream. These products are available over the counter and are frequently used to treat symptoms of atopic dermatitis. With allergic contact dermatitis, repeated exposure to allergens often worsens the condition.

Based on these findings, the researchers emphasize the importance of patch testing in children with atopic dermatitis.

“The results of this study underscore the need for children with (atopic dermatitis) to be referred to a specialist for evaluation of (allergic contact dermatitis),” wrote Johnson and her colleagues. “Uncovering potentially relevant contact allergens can lead to improvement in quality of life, can decrease use of topical steroids and systemic immunosuppressants, and can significantly lessen overall disease severity.”