Erythematous reactions on removal of Scanpor® tape in patch testing are not necessarily caused by dermographism.

Removal of Scanpor® tape after occlusion for 2 days in patch testing sometimes elicits a localized erythematous skin reaction under the tape. Usually, a ‘cooling-off period’ of a few minutes allows the erythema to fade, ensuring that weakly positive patch test results are not missed. This reaction is commonly believed to be a form of dermographism, a physical form of urticaria caused by a light shearing force being applied to the surface of the skin, resulting in various degrees of pruritus accompanied by whealing. The role of dermographism in such red reactions during patch testing has never been previously investigated. Additionally, within the field of cutaneous allergy, no formal population data exist on the current incidence of symptomatic dermographism in the general population, although the incidence of simple dermographism (a milder form with no pruritus) has been estimated to be ∼5% (1). This pilot study was designed to determine whether those with erythema in the occluded area after removal of Scanpor® tape had a history of dermographism or urticaria, and also whether they would show objective signs of dermographism on skin testing. Twenty consecutive patients with erythema on removal of Scanpor® tape during patch testing in our unit between October 2008 and February 2009 [median age 32 years, range 23–64 years; 5 (25%) male] were recruited to the study group. A further 9 consecutive patients with no erythema on removal of the tape were included as a control group. A history of dermographism or urticaria was recorded. Each patient was then tested for dermographism with a calibrated dermographometer (Hook & Tucker, Croydon,