Contact Dermatitis in Atopic Individuals

Allergic contact dermatitis and atopic dermatitis are common inflammatory T cell-mediated diseases, that often coexist. The prevalence of atopic dermatitis seems to have tripled in industrialized countries in the last three decades, affecting 15–30% of children and 2–10% of adults. Both conditions are associated with high costs for the health service, for loss of work or school days, and a reduced quality of life. There are various reasons why subjects with atopic dermatitis tend to have an increased risk of allergic contact dermatitis than non atopic subjects. Firstly, patients with atopic dermatitis have an altered skin barrier function, with an approximately two-fold increased skin contact absorption of irritants and sensitizing substances. Irritant chemicals, in turn, further affect the skin barrier, boosting the penetration of allergens and so increasing the risk of contact allergy. The chronic topical use of various emollients and anti-inflammatory drugs to treat the disease should also be borne in mind. Yet another factor is bacterial colonization in atopic dermatitis, that induces an inflammatory process than can lead to increased contact sensitization. The rates of positive patch tests in children with atopic dermatitis range widely, from 27 to 95.6%. The most common allergens are metals, lanolin, neomycin, and fragrances. Guideline for patch testing in subjects with atopic dermatitis are available, as well as the consideration about various pitfalls concerning the same tests.