The significance of previous allergic contact dermatitis for elicitation of delayed hypersensitivity to nickel.

Several factors, such as amount of allergen, vehicle, anatomic site, immunologic status and previous eczema, may influence delayed hypersensitivity reactions. In an extended model, we have studied the significance of previous allergic contact dermatitis for elicitation of delayed hypersensitivity to nickel in 25 nickel-allergic females. On 3 occasions, 8, 4 and 1 months before the final challenge patch testing, an experimental allergic contact dermatitis from nickel was induced on the lower back. At the challenge patch testing, 4 identical dilution series of nickel were tested on 4 areas on the lower back 3 with previous but healed dermatitis and 1 control area. The tests were read in a blind way. A significantly higher test reactivity was found at the areas with a previous allergic contact dermatitis, the shorter the time interval between the previous provocation and the challenge, the stronger the reaction. These results may be of importance for the understanding of factors contributing to chronicity of allergic contact dermatitis.