Photopatch test reactivity: effect of photoallergen concentration and UVA dosaging


  • T. Hasan,

    Corresponding author
    1. Department of Dermatology, University of Tampere and Tampere University Hospital, Finland
    • Taina Hasan, Department of Dermatology, Tampere University Hospital, PL 2000, FIN-33521 Tampere, Finland

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  • C. T. Jansen

    1. Department of Dermatology, University of Turku and The Turku University Central Hospital, Finland
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We have studied the influence of variations in allergen concentration and UVA dosaging on the results of photopatch testing with the Scandinavian standard photopatch series in 29 patients with photocontact and/or contact allergy to 1 or several of the allergens in that series. Photocontact test reactions were more sensitive to allergen dilution than plain contact test reactions. Even dilution from the standard 5% to 2.5% or 1.25% significantly reduced para-aminobenzoic acid photocontact test reactions. Reducing the UVA dose from the standard 5 J/cm2 to 2.5 or 1 J/cm2 in 2 out of 5 cases turned a significant (++) reaction into a doubtful one (+). Increasing the standard UVA dose of 5 J/cm2 to 20 – 40 J/cm2 turned a single + photocontact reaction to trichlorcarbanilide and a single 1 + plain contact reaction to chlorhexidine into ++ reactions. In the majority of eases, however, neither photocontact nor plain contact test reactions were augmented by UVA doses up to 80 J/cm2. We conclude that a UVA dose of 5 J/cm2 is sufficient for eliciting photocontact allergic test reactions, and that a reduction of either the UVA dose level or the standard allergen concentrations of the Scandinavian photopatch test guidelines may cause loss of significant photocontact test reactions in a proportion of the cases.