**2.5 Atopic dermatitis**

The association between atopic dermatitis and allergic contact dermatitis remains somewhat unclear. Several older studies that specifically investigated the prevalence of positive patch testing in children with atopic dermatitis suggested that contact allergy is less common in this population (Angelini & Meneghini, 1977). Jones et al. investigated sensitivity to Rhus in atopic and non-atopic patients. Patch tests to Rhus were positive in 61% of healthy patients and only 15% of those with atopic dermatitis (Jones et al., 1973). This correlation may be explained, as contact allergy is a Th1 response and atopic dermatitis patients have a decreased Th1 response (Mortz & Anderson, 1999). Alternatively, some studies suggest that allergic contact dermatitis is more frequent in atopic patients. Epstein and colleagues evaluated the frequency of positive patch tests in patients with atopic dermatitis versus those with psoriasis. Twenty-eight percent of those with atopic dermatitis had positive reactions versus 9% of those with psoriasis (Epstein & Mohajerin, 1964). Another study showed that patch tests were more frequently positive in those with atopic dermatitis versus controls without atopic dermatitis but with other allergic disease including allergic conjunctivitis and asthma (Lammintausta et al., 1992). Dotterud and Falk reported positive tests were significantly more common in schoolchildren with atopic dermatitis, 28.8%, versus 17.9% in controls (Dotterud & Falk, 1995). One explanation for increased risk in atopic patients is their defective skin barrier, which allows for increased exposure to antigens. Also, atopic patients may become sensitized to more allergens given their frequent use of topical agents including emollients, which often contain fragrances and preservatives (Mortz and Anderson, 1999). It should also be considered that atopic skin is readily irritated, which may lead to false positive patch testing results, especially in the case of metals (Dotterud & Falk, 1994). The latter concept is important as some recent studies did not detect a difference in the prevalence of positive patch testing between children with and without atopic dermatitis (Balato et al., 1989; Motolese et al., 1995).
